U.S. patent application number 15/980237 was filed with the patent office on 2018-09-13 for managing a divided load reorder queue.
The applicant listed for this patent is International Business Machines Corporation. Invention is credited to RICHARD J. EICKEMEYER, DAVID A. HRUSECKY, ELIZABETH A. MCGLONE, BRIAN W. THOMPTO, ALBERT J. VAN NORSTRAND, JR..
Application Number | 20180260230 15/980237 |
Document ID | / |
Family ID | 60677599 |
Filed Date | 2018-09-13 |
United States Patent
Application |
20180260230 |
Kind Code |
A1 |
EICKEMEYER; RICHARD J. ; et
al. |
September 13, 2018 |
MANAGING A DIVIDED LOAD REORDER QUEUE
Abstract
Managing a divided load reorder queue including storing load
instruction data for a load instruction in an expanded LRQ entry in
the LRQ; launching the load instruction from the expanded LRQ
entry; determining that the load instruction is in a finished
state; moving a subset of the load instruction data from the
expanded LRQ entry to a compact LRQ entry in the LRQ, wherein the
compact LRQ entry is smaller than the expanded LRQ entry; and
removing the load instruction data from the expanded LRQ entry.
Inventors: |
EICKEMEYER; RICHARD J.;
(ROCHESTER, MN) ; HRUSECKY; DAVID A.; (CEDAR PARK,
TX) ; MCGLONE; ELIZABETH A.; (ORONOCO, MN) ;
THOMPTO; BRIAN W.; (AUSTIN, TX) ; VAN NORSTRAND, JR.;
ALBERT J.; (ROUND ROCK, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
International Business Machines Corporation |
ARMONK |
NY |
US |
|
|
Family ID: |
60677599 |
Appl. No.: |
15/980237 |
Filed: |
May 15, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15193338 |
Jun 27, 2016 |
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15980237 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06F 9/3824 20130101;
G06F 9/3855 20130101; G06F 9/3857 20130101 |
International
Class: |
G06F 9/38 20180101
G06F009/38 |
Claims
1. A method of managing a divided load reorder queue (LRQ), the
method comprising: determining that a load instruction is in a
finished state; and moving a subset of load instruction data from
an expanded LRQ entry in the LRQ to a compact LRQ entry in the LRQ,
wherein the compact LRQ entry is smaller than the expanded LRQ
entry.
2. The method of claim 1, further comprising: determining that the
load instruction is in a completed state; and removing the subset
of the load instruction data from the compact LRQ entry in the
LRQ.
3. The method of claim 1, wherein moving the subset of the load
instruction data from the expanded LRQ entry to the compact LRQ
entry in the LRQ comprises: determining that at least one compact
LRQ entry is available to store the subset of the load instruction
data.
4. The method of claim 1, wherein moving the subset of the load
instruction data from the expanded LRQ entry to the compact LRQ
entry in the LRQ comprises: moving the load instruction data from
the expanded LRQ entry to a staging area; extracting the subset of
the load instruction data from the load instruction data; and
storing the extracted subset of the load instruction data in the
compact LRQ entry in the LRQ.
5. The method of claim 1, wherein the expanded LRQ entry is one of
a plurality of expanded LRQ entries in the LRQ, and wherein the
compact LRQ entry is one of a plurality of compact LRQ entries in
the LRQ.
6. The method of claim 1, wherein the subset of the load
instruction data comprises a hash of a portion of the load
instruction data.
7. The method of claim 1, wherein a size of the compact LRQ entry
is less than half of a size of the expanded LRQ entry.
8. A multi-slice processor configured to carry out: determining
that a load instruction is in a finished state; and moving a subset
of load instruction data from an expanded LRQ entry in the LRQ to a
compact LRQ entry in the LRQ, wherein the compact LRQ entry is
smaller than the expanded LRQ entry.
9. The multi-slice processor of claim 8, further configured to
carry out: determining that the load instruction is in a completed
state; and removing the subset of the load instruction data from
the compact LRQ entry in the LRQ.
10. The multi-slice processor of claim 8, wherein moving the subset
of the load instruction data from the expanded LRQ entry to the
compact LRQ entry in the LRQ comprises: determining that at least
one compact LRQ entry is available to store the subset of the load
instruction data.
11. The multi-slice processor of claim 8, wherein moving the subset
of the load instruction data from the expanded LRQ entry to the
compact LRQ entry in the LRQ comprises: moving the load instruction
data from the expanded LRQ entry to a staging area; extracting the
subset of the load instruction data from the load instruction data;
and storing the extracted subset of the load instruction data in
the compact LRQ entry in the LRQ.
12. The multi-slice processor of claim 8, wherein the expanded LRQ
entry is one of a plurality of expanded LRQ entries in the LRQ, and
wherein the compact LRQ entry is one of a plurality of compact LRQ
entries in the LRQ.
13. The multi-slice processor of claim 8, wherein the subset of the
load instruction data comprises a hash of a portion of the load
instruction data.
14. The multi-slice processor of claim 8, wherein a size of the
compact LRQ entry is less than half of a size of the expanded LRQ
entry.
15. An apparatus comprising a multi-slice processor configured to
carry out: determining that a load instruction is in a finished
state; and moving a subset of load instruction data from an
expanded LRQ entry in the LRQ to a compact LRQ entry in the LRQ,
wherein the compact LRQ entry is smaller than the expanded LRQ
entry.
16. The apparatus of claim 15, where in the multi-slice processor
is further configured to carry out: determining that the load
instruction is in a completed state; and removing the subset of the
load instruction data from the compact LRQ entry in the LRQ.
17. The apparatus of claim 15, wherein moving the subset of the
load instruction data from the expanded LRQ entry to the compact
LRQ entry in the LRQ comprises: determining that at least one
compact LRQ entry is available to store the subset of the load
instruction data.
18. The apparatus of claim 15, wherein moving the subset of the
load instruction data from the expanded LRQ entry to the compact
LRQ entry in the LRQ comprises: moving the load instruction data
from the expanded LRQ entry to a staging area; extracting the
subset of the load instruction data from the load instruction data;
and storing the extracted subset of the load instruction data in
the compact LRQ entry in the LRQ.
19. The apparatus of claim 15, wherein the expanded LRQ entry is
one of a plurality of expanded LRQ entries in the LRQ, and wherein
the compact LRQ entry is one of a plurality of compact LRQ entries
in the LRQ.
20. The apparatus of claim 15, wherein the subset of the load
instruction data comprises a hash of a portion of the load
instruction data.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation application of U.S.
patent application Ser. No. 15/193,338, filed Jun 27, 2016.
BACKGROUND
Field of the Invention
[0002] The field of the invention is data processing, or, more
specifically, methods, apparatus, and products for managing a
divided load reorder queue.
Description Of Related Art
[0003] The development of the EDVAC computer system of 1948 is
often cited as the beginning of the computer era. Since that time,
computer systems have evolved into extremely complicated devices.
Today's computers are much more sophisticated than early systems
such as the EDVAC. Computer systems typically include a combination
of hardware and software components, application programs,
operating systems, processors, buses, memory, input/output devices,
and so on. As advances in semiconductor processing and computer
architecture push the performance of the computer higher and
higher, more sophisticated computer software has evolved to take
advantage of the higher performance of the hardware, resulting in
computer systems today that are much more powerful than just a few
years ago.
[0004] One area of computer system technology that has advanced is
computer processors. As the number of computer systems in data
centers and the number of mobile computing devices has increased,
the need for more efficient computer processors has also increased.
Speed of operation and power consumption are just two areas of
computer processor technology that affect efficiency of computer
processors.
SUMMARY
[0005] Methods and apparatus for managing a divided load reorder
queue (LRQ) are disclosed in this specification. Managing a divided
LRQ includes storing load instruction data for a load instruction
in an expanded LRQ entry in the LRQ; launching the load instruction
from the expanded LRQ entry; determining that the load instruction
is in a finished state; moving a subset of the load instruction
data from the expanded LRQ entry to a compact LRQ entry in the LRQ,
wherein the compact LRQ entry is smaller than the expanded LRQ
entry; and removing the load instruction data from the expanded LRQ
entry.
[0006] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
descriptions of exemplary embodiments of the invention as
illustrated in the accompanying drawings wherein like reference
numbers generally represent like parts of exemplary embodiments of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 sets forth a block diagram of an example system
configured for managing a divided load reorder queue (LRQ)
according to embodiments of the present invention.
[0008] FIG. 2 sets forth a block diagram of a portion of a
multi-slice processor according to embodiments of the present
invention.
[0009] FIG. 3 sets forth a block diagram of a portion of a
load/store slice of a multi-slice processor according to
embodiments of the present invention.
[0010] FIG. 4 sets forth a flow chart illustrating an exemplary
method for managing a divided LRQ according to embodiments of the
present invention.
[0011] FIG. 5 sets forth a flow chart illustrating an exemplary
method for managing a divided LRQ according to embodiments of the
present invention.
[0012] FIG. 6 sets forth a flow chart illustrating an exemplary
method for managing a divided LRQ according to embodiments of the
present invention.
DETAILED DESCRIPTION
[0013] Exemplary methods and apparatus for managing a divided load
reorder queue (LRQ) in accordance with the present invention are
described with reference to the accompanying drawings, beginning
with FIG. 1. FIG. 1 sets forth a block diagram of an example system
configured managing a divided LRQ according to embodiments of the
present invention. The system of FIG. 1 includes an example of
automated computing machinery in the form of a computer (152).
[0014] The computer (152) of FIG. 1 includes at least one computer
processor (156) or `CPU` as well as random access memory (168)
(`RAM`) which is connected through a high speed memory bus (166)
and bus adapter (158) to processor (156) and to other components of
the computer (152).
[0015] The example computer processor (156) of FIG. 1 may be
implemented as a multi-slice processor. The term `multi-slice` as
used in this specification refers to a processor having a plurality
of similar or identical sets of components, where each set may
operate independently of all the other sets or in concert with the
one or more of the other sets. The multi-slice processor (156) of
FIG. 1, for example, includes several execution slices (`ES`) and
several load/store slices (`LSS`)--where load/store slices may
generally be referred to as load/store units. Each execution slice
may be configured to provide components that support execution of
instructions: an issue queue, general purpose registers, a history
buffer, an arithmetic logic unit (including a vector scalar unit, a
floating point unit, and others), and the like. Each of the
load/store slices may be configured with components that support
data movement operations such as loading of data from cache or
memory or storing data in cache or memory. In some embodiments,
each of the load/store slices includes a data cache. The load/store
slices are coupled to the execution slices through a results bus.
In some embodiments, each execution slice may be associated with a
single load/store slice to form a single processor slice. In some
embodiments, multiple processor slices may be configured to operate
together.
[0016] The example multi-slice processor (156) of FIG. 1 may also
include, in addition to the execution and load/store slices, other
processor components. In the system of FIG. 1, the multi-slice
processor (156) includes fetch logic, dispatch logic, and branch
prediction logic. Further, although in some embodiments each
load/store slice includes cache memory, the multi-slice processor
(156) may also include cache accessible by any or all of the
processor slices.
[0017] Although the multi-slice processor (156) in the example of
FIG. 1 is shown to be coupled to RAM (168) through a front side bus
(162), a bus adapter (158) and a high speed memory bus (166),
readers of skill in the art will recognize that such configuration
is only an example implementation. In fact, the multi-slice
processor (156) may be coupled to other components of a computer
system in a variety of configurations. For example, the multi-slice
processor (156) in some embodiments may include a memory controller
configured for direct coupling to a memory bus (166). In some
embodiments, the multi-slice processor (156) may support direct
peripheral connections, such as PCIe connections and the like.
[0018] Stored in RAM (168) in the example computer (152) is a data
processing application (102), a module of computer program
instructions that when executed by the multi-slice processor (156)
may provide any number of data processing tasks. Examples of such
data processing applications may include a word processing
application, a spreadsheet application, a database management
application, a media library application, a web server application,
and so on as will occur to readers of skill in the art. Also stored
in RAM (168) is an operating system (154). Operating systems useful
in computers configured for operation of a multi-slice processor
according to embodiments of the present invention include UNIX.TM.,
Linux.TM., Microsoft Windows.TM., AIX.TM., IBM's z/OS.TM., and
others as will occur to those of skill in the art. The operating
system (154) and data processing application (102) in the example
of FIG. 1 are shown in RAM (168), but many components of such
software typically are stored in non-volatile memory also, such as,
for example, on a disk drive (170).
[0019] The computer (152) of FIG. 1 includes disk drive adapter
(172) coupled through expansion bus (160) and bus adapter (158) to
processor (156) and other components of the computer (152). Disk
drive adapter (172) connects non-volatile data storage to the
computer (152) in the form of disk drive (170). Disk drive adapters
useful in computers configured for operation of a multi-slice
processor according to embodiments of the present invention include
Integrated Drive Electronics (`IDE`) adapters, Small Computer
System Interface (`SCSI`) adapters, and others as will occur to
those of skill in the art. Non-volatile computer memory also may be
implemented for as an optical disk drive, electrically erasable
programmable read-only memory (so-called `EEPROM` or `Flash`
memory), RAM drives, and so on, as will occur to those of skill in
the art.
[0020] The example computer (152) of FIG. 1 includes one or more
input/output (`I/O`) adapters (178). I/O adapters implement
user-oriented input/output through, for example, software drivers
and computer hardware for controlling output to display devices
such as computer display screens, as well as user input from user
input devices (181) such as keyboards and mice. The example
computer (152) of FIG. 1 includes a video adapter (209), which is
an example of an I/O adapter specially designed for graphic output
to a display device (180) such as a display screen or computer
monitor. Video adapter (209) is connected to processor (156)
through a high speed video bus (164), bus adapter (158), and the
front side bus (162), which is also a high speed bus.
[0021] The exemplary computer (152) of FIG. 1 includes a
communications adapter (167) for data communications with other
computers (182) and for data communications with a data
communications network (100). Such data communications may be
carried out serially through RS-232 connections, through external
buses such as a Universal Serial Bus (`USB`), through data
communications networks such as IP data communications networks,
and in other ways as will occur to those of skill in the art.
Communications adapters implement the hardware level of data
communications through which one computer sends data communications
to another computer, directly or through a data communications
network. Examples of communications adapters useful in computers
configured for operation of a multi-slice processor according to
embodiments of the present invention include modems for wired
dial-up communications, Ethernet (IEEE 802.3) adapters for wired
data communications, and 802.11 adapters for wireless data
communications.
[0022] The arrangement of computers and other devices making up the
exemplary system illustrated in FIG. 1 are for explanation, not for
limitation. Data processing systems useful according to various
embodiments of the present invention may include additional
servers, routers, other devices, and peer-to-peer architectures,
not shown in FIG. 1, as will occur to those of skill in the art.
Networks in such data processing systems may support many data
communications protocols, including for example TCP (Transmission
Control Protocol), IP (Internet Protocol), HTTP (HyperText Transfer
Protocol), WAP (Wireless Access Protocol), HDTP (Handheld Device
Transport Protocol), and others as will occur to those of skill in
the art. Various embodiments of the present invention may be
implemented on a variety of hardware platforms in addition to those
illustrated in FIG. 1.
[0023] For further explanation, FIG. 2 sets forth a block diagram
of a portion of a multi-slice processor according to embodiments of
the present invention. The multi-slice processor in the example of
FIG. 2 includes a dispatch network (202). The dispatch network
(202) includes logic configured to dispatch instructions for
execution among execution slices.
[0024] The multi-slice processor in the example of FIG. 2 also
includes a number of execution slices (204a, 204b-204n). Each
execution slice includes general purpose registers (206) and a
history buffer (208). The general purpose registers and history
buffer may sometimes be referred to as the mapping facility, as the
registers are utilized for register renaming and support logical
registers.
[0025] The general purpose registers (206) are configured to store
the youngest instruction targeting a particular logical register
and the result of the execution of the instruction. A logical
register is an abstraction of a physical register that enables
out-of-order execution of instructions that target the same
physical register.
[0026] When a younger instruction targeting the same particular
logical register is received, the entry in the general purpose
register is moved to the history buffer, and the entry in the
general purpose register is replaced by the younger instruction.
The history buffer (208) may be configured to store many
instructions targeting the same logical register. That is, the
general purpose register is generally configured to store a single,
youngest instruction for each logical register while the history
buffer may store many, non-youngest instructions for each logical
register.
[0027] Each execution slice (204) of the multi-slice processor of
FIG. 2 also includes an execution reservation station (210). The
execution reservation station (210) may be configured to issue
instructions for execution. The execution reservation station (210)
may include an issue queue. The issue queue may include an entry
for each operand of an instruction. The execution reservation
station may issue the operands for execution by an arithmetic logic
unit or to a load/store slice (222a, 222b, 222c) via the results
bus (220).
[0028] The arithmetic logic unit (212) depicted in the example of
FIG. 2 may be composed of many components, such as add logic,
multiply logic, floating point units, vector/scalar units, and so
on. Once an arithmetic logic unit executes an operand, the result
of the execution may be stored in the result buffer (214) or
provided on the results bus (220) through a multiplexer (216).
[0029] The results bus (220) may be configured in a variety of
manners and be of composed in a variety of sizes. In some
instances, each execution slice may be configured to provide
results on a single bus line of the results bus (220). In a similar
manner, each load/store slice may be configured to provide results
on a single bus line of the results bus (220). In such a
configuration, a multi-slice processor with four processor slices
may have a results bus with eight bus lines--four bus lines
assigned to each of the four load/store slices and four bus lines
assigned to each of the four execution slices. Each of the
execution slices may be configured to snoop results on any of the
bus lines of the results bus. In some embodiments, any instruction
may be dispatched to a particular execution unit and then by issued
to any other slice for performance. As such, any of the execution
slices may be coupled to all of the bus lines to receive results
from any other slice. Further, each load/store slice may be coupled
to each bus line in order to receive an issue load/store
instruction from any of the execution slices. Readers of skill in
the art will recognize that many different configurations of the
results bus may be implemented.
[0030] The multi-slice processor in the example of FIG. 2 also
includes a number of load/store slices (222a, 222b-222n). Each
load/store slice includes a queue (224), a multiplexer (228), a
data cache (232), and formatting logic (226), among other
components described below with regard to FIG. 3. The queue
receives load and store operations to be carried out by the
load/store slice (222). The formatting logic (226) formats data
into a form that may be returned on the results bus (220) to an
execution slice as a result of a load or store instruction.
[0031] The example multi-slice processor of FIG. 2 may be
configured for flush and recovery operations. A flush and recovery
operation is an operation in which the registers (general purpose
register and history buffer) of the multi-slice processor are
effectively `rolled back` to a previous state. The term `restore`
and `recover` may be used, as context requires in this
specification, as synonyms. Flush and recovery operations may be
carried out for many reasons, including missed branch predictions,
exceptions, and the like. Consider, as an example of a typical
flush and recovery operation, that a dispatcher of the multi-slice
processor dispatches over time and in the following order: an
instruction A targeting logical register 5, an instruction B
targeting logical register 5, and an instruction C targeting
logical register 5. At the time instruction A is dispatched, the
instruction parameters are stored in the general purpose register
entry for logical register 5. Then, when instruction B is
dispatched, instruction A is evicted to the history buffer (all
instruction parameters are copied to the history buffer, including
the logical register and the identification of instruction B as the
evictor of instruction A), and the parameters of instruction B are
stored in the general purpose register entry for logical register
5. When instruction C is dispatched, instruction B is evicted to
the history buffer and the parameters of instruction C are stored
in the general purpose register entry for logical register 5.
Consider, now, that a flush and recovery operation of the registers
is issued in which the dispatch issues a flush identifier matching
the identifier of instruction C. In such an example, flush and
recovery includes discarding the parameters of instruction C in the
general purpose register entry for logical register 5 and moving
the parameters of instruction B from the history buffer for
instruction B back into the entry of general purpose register for
logical register 5.
[0032] During the flush and recovery operation, in prior art
processors, the dispatcher was configured to halt dispatch of new
instructions to an execution slice. Such instructions may be
considered either target or source instructions. A target
instruction is an instruction that targets a logical register for
storage of result data. A source instruction by contrast has, as
its source, a logical register. A target instruction, when
executed, will result in data stored in an entry of a register file
while a source instruction utilizes such data as a source for
executing the instruction. A source instruction, while utilizing
one logical register as its source, may also target another logical
register for storage of the results of instruction. That is, with
respect to one logical register, an instruction may be considered a
source instruction and with respect to another logical register,
the same instruction may be considered a target instruction.
[0033] The multi-slice processor in the example of FIG. 2 also
includes an instruction sequencing unit (240). While depicted as a
single unit, each of the plurality of execution slices may include
a respective instruction sequencing unit similar to instruction
sequencing unit (240). Instruction sequencing unit (240) may take
dispatched instructions and check dependencies of the instructions
to determine whether all older instructions with respect to a
current instruction have delivered, or may predictably soon
deliver, results of these older instructions from which the current
instruction is dependent so that the current instruction may
execute correctly. If all dependencies to a current instruction are
satisfied, then a current instruction may be determined to be ready
to issue, and may consequently be issued--regardless of a program
order of instructions as determined by an ITAG. Such issuance of
instructions may be referred to as an "out-of-order" execution, and
the multi-slice processor may be considered an out-of-order
machine.
[0034] In some cases, a load/store unit receiving an issued
instruction, such as a load/store slice, may not yet be able to
handle the instruction, and the instruction sequencing unit (240)
may keep the instruction queued until such time as the load/store
slice may handle the instruction. After the instruction is issued,
the instruction sequencing unit (240) may track progress of the
instruction based at least in part on signals received from a
load/store slice.
[0035] For further explanation, FIG. 3 sets forth a block diagram
depicting an expanded view of a load/store slice (222a)
implementing architectural components that include a load/store
access queue (LSAQ) (224), a load reorder queue (LRQ) (304), a load
miss queue (LMQ) (308), a store reorder queue (SRQ) (306), a data
cache (232), among other components. The load/store access queue
(224) may propagate an instruction through MUX (228) along line
(316) to the load reorder queue (304) or the store reorder queue
(306).
[0036] In previous systems, if a load/store unit received an
instruction from an instruction sequencing unit, and the load/store
unit was unable to handle the instruction for some reason, then the
load/store unit would notify the instruction sequencing unit that
the instruction was being rejected and the load/store unit would
discard information related to the rejected instruction. In which
case, the instruction sequencing unit would continue maintaining
information to track and maintain the rejected instruction until
the instruction is resent to the load/store unit. An instruction
may be rejected for a variety of reasons, including an address miss
in an address translation cache, a set prediction miss, data cache
banking collisions, an overload of the load miss queue (308), among
other possible rejection conditions.
[0037] The load/store slice (222a), by contrast to the above
previous system, is configured to determine a rejection condition
for an instruction received from an instruction sequencing unit,
however, the load/store slice (222a), instead of sending a reject
signal to the instruction sequencing unit, maintains tracking and
handling of the instruction--including information usable to
relaunch or reissue the instruction--until the rejection condition
is resolved. Further, an entry in the load reorder queue (304) or
the store reorder queue (306) may be configured to maintain
information for tracking an instruction that would otherwise have
been rejected and removed from the load reorder queue (304). For
example, if the load/store slice (222a) determines that a rejection
condition exists for a given load or store instruction, then logic
within the load/store slice may notify the load reorder queue (304)
or the store reorder queue (306) to place the instruction in a
sleep state for a given number of cycles, or to place the
instruction in a sleep state until notified to awaken, or to
immediately reissue the instruction, among other notifications to
perform other operations.
[0038] In this way, the load/store slice (222a) may save cycles
that would otherwise be lost if the instruction were rejected to
the instruction sequencing unit because the load/store slice (222a)
may more efficiently and quickly reissue the instruction when the
rejection condition is resolved in addition to more quickly
detecting resolution of a rejection condition than an instruction
sequencing unit. For example, if the load/store slice (222a)
determines that an instruction that is in a sleep state may be
reissued in response to determining that one or more rejection
conditions have been resolved preventing the instruction from
completing, then the load/store store slice may notify the load
reorder queue (304) or the store reorder queue (306) to relaunch or
reissue the instruction immediately or after some number of cycles.
The number of cycles may depend upon a type of rejection condition
or upon other factors affecting reissue or relaunch of the
instruction. In this example, the load reorder queue (304) or the
store reorder queue (306) may reissue or relaunch an instruction by
providing the load/store access queue (224) with information to
reissue the instruction, where the load reorder queue (304) or the
store reorder queue (306) may communicate with the load/store
access queue (224) along line (314) and may provide data for
reissuing or relaunching the instruction along line (313).
[0039] Another improvement that results from the load/store slice
(222a) maintaining an instruction if a rejection condition is
determined is that the load/store slice (222a) uses fewer
resources, such as logic and circuitry for latches and other
components, to maintain the instruction than an instruction
sequencing unit. In other words, given that the instruction
sequencing unit may rely on the load/store slice (222a) in handling
the instruction to completion, the instruction sequencing unit may
free resources once the instruction is provided to the load/store
slice (222a).
[0040] Further, the instruction sequencing unit (240), based at
least in part on communications with the load/store slice (222a),
may determine when and whether to wake instructions that may be
dependent on a current instruction being handled by the load/store
slice (222a). Therefore, if the load/store slice (222a) determines
that a rejection condition exists, the load/store slice (222a)
delays a notification to the instruction sequencing unit (240) to
awaken dependent instructions to prevent the instruction sequencing
unit (240) from issuing dependent instructions that are
subsequently unable to finish due to lack of availability of
results from a current instruction. In this way, the instruction
sequencing unit (240) may avoid wasting execution cycles reissuing
dependent instructions that are unable to finish.
[0041] For example, the load/store slice (222a) may communicate
with the instruction sequencing unit (240) through the generation
of signals indicating, at different points in handling a load
instruction, that a load instruction is to be reissued or that data
for a load instruction is valid. In some cases, in response to the
instruction sequencing unit (240) receiving a signal from the
load/store slice (222a) that a given instruction is to be reissued,
the instruction sequencing unit (240) may awaken instructions
dependent upon the given instruction with the expectation that the
given instruction, after being reissued, is going to finish and
provide valid data.
[0042] The load/store slice (222a) may also retrieve data from any
tier of a memory hierarchy, beginning with a local data cache
(232), and extending as far down in the hierarchy as needed to find
requested data. The requested data, when received, may be provided
to general purpose registers, virtual registers, or to some other
destination. The received data may also be stored in a data cache
(232) for subsequent access. The load/store slice (222a) may also
manage translations of effective addresses to real addresses to
communicate with different levels of memory hierarchy.
[0043] A store reorder queue (306) may include entries for tracking
the cache operations for sequential consistency and may reissue
operations into the load/store pipeline for execution independent
of an execution slice.
[0044] A load miss queue (308) may issue requests for data to one
or more data storage devices of a multi-tiered memory hierarchy,
where a request for data may correspond to a load instruction for
the data.
[0045] Responsive to the data being returned along the line (302)
to the load/store slice (222a), the data may be delivered to a
destination such as the results bus (220 of FIG. 2) to be loaded
into, for example, a general purpose register--where the delivery
of the data may be from the data cache (232) or over the line
(310). The line (310) bypasses the data cache (232) and allows
implementation of a critical data forwarding path. The load reorder
queue (304) may also use line (312) to notify an instruction
sequencing unit, or some other logical component, that the data is
available.
[0046] A load reorder queue (304) may track execution of cache
operations issued to the load/store slice (222a) and includes
entries for tracking cache operations for sequential consistency,
among other attributes. The load reorder queue (304) may also
reissue operations into the load/store pipeline for execution,
which provides operation that is independent of the execution
slices.
[0047] For further explanation, FIG. 4 sets forth a flow chart
illustrating an exemplary method for managing a divided LRQ. The
method of FIG. 4 may be carried out by a multi-slice processor
similar to that in the examples of FIGS. 1-3. Such a multi-slice
processor may include an instruction sequencing unit (240), and a
plurality of load/store slices (222a-222n), where each of the
load/store slices may implement a load/store access queue (224), a
load reorder queue (304), and a store reorder queue (306), as
described above with regard to FIG. 3.
[0048] The method of FIG. 4 includes storing (402) load instruction
data for a load instruction in an expanded LRQ entry in the LRQ
(304). Storing (402) load instruction data for a load instruction
in an expanded LRQ entry in the LRQ (304) may be carried out by the
instruction sequencing unit (240) issuing the load instruction to
the LSS (222), and the LSS (222) storing the load instruction data
in the expanded LRQ entry in the LRQ (304).
[0049] The LRQ (304) may be divided in that the LRQ (304) may
include at least two entries that are different sizes. The divided
LRQ (304) may include one set (i.e., a plurality) of entries that
are one size (e.g., 300 bits), and one set (i.e., a plurality) of
entries that are another size (e.g., 50 bits). The larger entries
may be referred to as expanded LRQ entries, and the smaller entries
may be referred to as compact LRQ entries. The divided LRQ (304)
may include one or a plurality of expanded LRQ entries and one or a
plurality of compact LRQ entries.
[0050] An expanded LRQ entry may be configured to store load
instruction data about a load instruction. A load instruction is an
instruction that reads data from memory (such as data cache (232)
and stores that data in a register. The load instruction may be an
internal operation decoded from a processor instruction.
[0051] The load instruction data may include the load instruction
and other data describing the load instruction. The load
instruction data stored in the expanded LRQ entry may include
instruction operation codes, effective address information to
determine the bytes within a cacheline that are involved in the
load, an instruction identifier (e.g., an ITAG), a real address
that describes the cacheline address used by lower levels of memory
hierarchy, an associated LMQ (308) entry, and state of the load
instruction for relaunch. After the load instruction is issued and
stored in the expanded LRQ entry, but before the load instruction
has finished, information in the load instruction data is used by
the LSS (222) for launching the load instruction.
[0052] The method of FIG. 4 includes launching (404) the load
instruction from the expanded LRQ entry. Launching (404) the load
instruction from the expanded LRQ entry may be carried out by
initiating the load process described by the load instruction and
the load instruction data. Launching (404) the load instruction
from the expanded LRQ entry may include other processing performed
in service of the load instruction, such as address fetches, data
cache lookups, and data fetches. Launching the load instruction may
also include relaunching the load instruction (e.g., in the event
that incorrect data was read from the data cache (232) during the
initial or a previous launch).
[0053] The method of FIG. 4 includes determining (406) that the
load instruction is in a finished state. Determining (406) that the
load instruction is in a finished state may be carried out by
determining that an indication has been received that the load
instruction has successfully been executed (e.g., data targeted by
the load instruction has been placed in a register). Specifically,
determining (406) that the load instruction is in a finished state
may be carried out by determining that a load instruction is in the
finished state based on a pipeline stage of the load instruction.
Once the cycle associated with the load instruction finish has
concluded, and the LSS (222) receives valid bits associated with
that cycle, the LSS (222) may determine that the load instruction
has entered the finish state. The determination that the load
instruction is in a finished state may be made at any point during
the finish state of the load instruction.
[0054] The finished state may describe the state of a load
instruction after the load instruction has finished (i.e., an
indication has been received that the load instruction has
successfully been executed) but before the load instruction has
completed (i.e., an indication has been received that the load
instruction data is no longer needed). A finished state is a state
of the load instruction during which a large portion of the
information in the load instruction data is no longer used.
Specifically, the finished state indicates that the load
instruction will no longer need to be relaunched and the load
instruction will no longer need to fetch data from memory (such as
the level 2 cache). The finished state may further indicate that
data associated with the execution of the load instruction has been
sent to the instruction sequencing unit (240), but the load
instruction may still be out-of-order.
[0055] The method of FIG. 4 includes moving (408) a subset of the
load instruction data from the expanded LRQ entry to a compact LRQ
entry in the LRQ (304), wherein the compact LRQ entry is smaller
than the expanded LRQ entry. Moving (408) a subset of the load
instruction data from the expanded LRQ entry to a compact LRQ entry
in the LRQ (304), wherein the compact LRQ entry is smaller than the
expanded LRQ entry may be carried out in response to a
determination that the load instruction is in a finished state.
Further, moving (408) a subset of the load instruction data from
the expanded LRQ entry to a compact LRQ entry in the LRQ (304),
wherein the compact LRQ entry is smaller than the expanded LRQ
entry may be carried out by determining that at least one compact
LRQ entry is available to store the subset of the load instruction
data; moving the load instruction data from the expanded LRQ entry
to a staging area; extracting the subset of the load instruction
data from the load instruction data; and storing the extracted
subset of the load instruction data in the compact LRQ entry in the
LRQ (304).
[0056] The subset of the load instruction data is the portion of
the load instruction data that includes some, but not all, of the
information in the load instruction data. The subset of the load
instruction data may include only the necessary information to
perform one or more tasks. For example, the subset of the load
instruction data may include information for maintaining load
ordering, such as a real address, age information (e.g., using an
instruction identifier or ITAG), byte flags, and snoop
information.
[0057] Further, the information in the subset of the load
instruction data may be stored in an altered form. For example, a
hash of one or more portions, fields, or elements of the subset of
the load instruction data may be stored instead of the full
portion, field or element. For example, a hash of the real address
may be stored in the compact LRQ entry instead of the full real
address. Using a hash of the information may conserve space within
the compact LRQ entry.
[0058] The method of FIG. 4 includes removing (410) the load
instruction data from the expanded LRQ entry. Removing (410) the
load instruction data from the expanded LRQ entry may be carried
out by setting a flag within an element of the expanded LRQ entry
indicating that the expanded LRQ entry is no longer valid, and is
free for storage of the load instruction data of another load
instruction.
[0059] For further explanation, FIG. 5 sets forth a flow chart
illustrating an exemplary method for managing a divided LRQ
according to embodiments of the present invention that includes
storing (402) load instruction data for a load instruction in an
expanded LRQ entry in the LRQ (304); launching (404) the load
instruction from the expanded LRQ entry; determining (406) that the
load instruction is in a finished state; moving (408) a subset of
the load instruction data from the expanded LRQ entry to a compact
LRQ entry in the LRQ (304), wherein the compact LRQ entry is
smaller than the expanded LRQ entry; and removing (410) the load
instruction data from the expanded LRQ entry.
[0060] The method of FIG. 5 differs from the method of FIG. 4,
however, in that the method of FIG. 5 further includes determining
(502) that the load instruction is in a completed state; and
removing (504) the subset of the load instruction data from the
compact LRQ entry in the LRQ (304). Determining (502) that the load
instruction is in a completed state may be carried out by
determining that a load instruction is in the completed state based
receiving an indication that the load instruction data for the load
instruction is no longer needed. Such an indication may be sent by
the instruction sequencing unit (240), and received by the LRQ
(304). The indication may include a completion valid flag and an
identifier (e.g., an ITAG) of the completed instruction. The
completed instruction may be the last sequential instruction that
has completed, indicating all older instructions have also
completed.
[0061] The completed state may describe the state of a load
instruction after the load instruction has completed (i.e., an
indication has been received that the load instruction data is no
longer needed). A completed state is a state of the load
instruction during which none of the load instruction data is
needed by any other element in the system. Specifically, the
completed state indicates that the load instruction data is no
longer needed to determine the order of other instructions.
[0062] Removing (504) the subset of the load instruction data from
the compact LRQ entry in the LRQ (304) may be carried out by
comparing the identifier of the completed instruction received from
the instruction sequencing unit (240) to the identifier for each
load instruction stored in the LRQ (304). This may include both
expanded LRQ entries and compact LRQ entries. If the identifier for
the load instruction is less than (or equal to) the completed
instruction identifier, then the load instruction data is removed
from the LRQ entry. Removing (504) the subset of the load
instruction data from the compact LRQ entry in the LRQ (304) may
also be carried out by setting a flag within an element of the
compact LRQ entry indicating that the compact LRQ entry is no
longer valid, and is free for storage of a subset of load
instruction data of another load instruction.
[0063] For further explanation, FIG. 6 sets forth a flow chart
illustrating an exemplary method for managing a divided LRQ
according to embodiments of the present invention that includes
storing (402) load instruction data for a load instruction in an
expanded LRQ entry in the LRQ (304); launching (404) the load
instruction from the expanded LRQ entry; determining (406) that the
load instruction is in a finished state; moving (408) a subset of
the load instruction data from the expanded LRQ entry to a compact
LRQ entry in the LRQ (304), wherein the compact LRQ entry is
smaller than the expanded LRQ entry; and removing (410) the load
instruction data from the expanded LRQ entry.
[0064] The method of FIG. 6 differs from the method of FIG. 4,
however, in that moving (408) a subset of the load instruction data
from the expanded LRQ entry to a compact LRQ entry in the LRQ
(304), wherein the compact LRQ entry is smaller than the expanded
LRQ entry includes determining (602) that at least one compact LRQ
entry is available to store the subset of the load instruction
data; moving (604) the load instruction data from the expanded LRQ
entry to a staging area; extracting (606) the subset of the load
instruction data from the load instruction data; and storing (608)
the extracted subset of the load instruction data in the compact
LRQ entry in the LRQ (304).
[0065] Determining (602) that at least one compact LRQ entry is
available to store the subset of the load instruction data may be
carried out by traversing each compact LRQ entry and reading a
valid bit for each compact LRQ entry. Determining (602) that at
least one compact LRQ entry is available to store the subset of the
load instruction data may further be carried out by determining the
entry identifier of one compact LRQ entry that does not have a
valid bit set indicating that new load instruction data (or more
specifically, a subset of load instruction data) may be stored in
that compact LRQ entry.
[0066] Moving (604) the load instruction data from the expanded LRQ
entry to a staging area may be carried out by transferring the load
instruction data (or a subset of the load instruction data) from
the expanded LRQ entry to a staging area. The staging area may be a
data storage location configured to store the load instruction data
or a subset of the load instruction data. The staging area may be a
special purpose register, a location in memory, or a special entry
in the LRQ (304).
[0067] Extracting (606) the subset of the load instruction data
from the load instruction data may be carried out by selecting one
or more portions, fields, or elements from the load instruction
data for storage in the compact LRQ entry. Extracting (606) the
subset of the load instruction data from the load instruction data
may also be carried out by modifying a portion, field, or element
of the load instruction data. For example, a hash may be taken of
one or more portions, fields, or elements of the load instruction
data (e.g. hashing the real address), and the hash of the one or
more portions, fields, or elements may be stored as a part of the
subset of the load instruction data.
[0068] Extracting (606) the subset of the load instruction data
from the load instruction data may be performed prior to, or
concurrently with, moving the load instruction data to the staging
area or storing the extracted subset of the load instruction in the
compact LRQ entry. For example, a portion of the load instruction
data may be moved from the expanded LRQ entry or from the staging
area and the remaining portion not within the subset of load
instruction data may remain in the expanded LRQ entry or staging
area to be overwritten.
[0069] Storing (608) the extracted subset of the load instruction
data in the compact LRQ entry in the LRQ (304) may be carried out
by transferring the subset of the load instruction data from the
staging area to the compact LRQ entry.
[0070] Exemplary embodiments of the present invention are described
largely in the context of a fully functional computer system for
managing a divided load reorder queue. Readers of skill in the art
will recognize, however, that the present invention also may be
embodied in a computer program product disposed upon computer
readable storage media for use with any suitable data processing
system. Such computer readable storage media may be any storage
medium for machine-readable information, including magnetic media,
optical media, or other suitable media. Examples of such media
include magnetic disks in hard drives or diskettes, compact disks
for optical drives, magnetic tape, and others as will occur to
those of skill in the art. Persons skilled in the art will
immediately recognize that any computer system having suitable
programming means will be capable of executing the steps of the
method of the invention as embodied in a computer program product.
Persons skilled in the art will recognize also that, although some
of the exemplary embodiments described in this specification are
oriented to software installed and executing on computer hardware,
nevertheless, alternative embodiments implemented as firmware or as
hardware are well within the scope of the present invention.
[0071] The present invention may be a system, a method, and/or a
computer program product. The computer program product may include
a computer readable storage medium (or media) having computer
readable program instructions thereon for causing a processor to
carry out aspects of the present invention.
[0072] The computer readable storage medium can be a tangible
device that can retain and store instructions for use by an
instruction execution device. The computer readable storage medium
may be, for example, but is not limited to, an electronic storage
device, a magnetic storage device, an optical storage device, an
electromagnetic storage device, a semiconductor storage device, or
any suitable combination of the foregoing. A non-exhaustive list of
more specific examples of the computer readable storage medium
includes the following: a portable computer diskette, a hard disk,
a random access memory (RAM), a read-only memory (ROM), an erasable
programmable read-only memory (EPROM or Flash memory), a static
random access memory (SRAM), a portable compact disc read-only
memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a
floppy disk, a mechanically encoded device such as punch-cards or
raised structures in a groove having instructions recorded thereon,
and any suitable combination of the foregoing. A computer readable
storage medium, as used herein, is not to be construed as being
transitory signals per se, such as radio waves or other freely
propagating electromagnetic waves, electromagnetic waves
propagating through a waveguide or other transmission media (e.g.,
light pulses passing through a fiber-optic cable), or electrical
signals transmitted through a wire.
[0073] Computer readable program instructions described herein can
be downloaded to respective computing/processing devices from a
computer readable storage medium or to an external computer or
external storage device via a network, for example, the Internet, a
local area network, a wide area network and/or a wireless network.
The network may comprise copper transmission cables, optical
transmission fibers, wireless transmission, routers, firewalls,
switches, gateway computers and/or edge servers. A network adapter
card or network interface in each computing/processing device
receives computer readable program instructions from the network
and forwards the computer readable program instructions for storage
in a computer readable storage medium within the respective
computing/processing device.
[0074] Computer readable program instructions for carrying out
operations of the present invention may be assembler instructions,
instruction-set-architecture (ISA) instructions, machine
instructions, machine dependent instructions, microcode, firmware
instructions, state-setting data, or either source code or object
code written in any combination of one or more programming
languages, including an object oriented programming language such
as Smalltalk, C++ or the like, and conventional procedural
programming languages, such as the "C" programming language or
similar programming languages. The computer readable program
instructions may execute entirely on the user's computer, partly on
the user's computer, as a stand-alone software package, partly on
the user's computer and partly on a remote computer or entirely on
the remote computer or server. In the latter scenario, the remote
computer may be connected to the user's computer through any type
of network, including a local area network (LAN) or a wide area
network (WAN), or the connection may be made to an external
computer (for example, through the Internet using an Internet
Service Provider). In some embodiments, electronic circuitry
including, for example, programmable logic circuitry,
field-programmable gate arrays (FPGA), or programmable logic arrays
(PLA) may execute the computer readable program instructions by
utilizing state information of the computer readable program
instructions to personalize the electronic circuitry, in order to
perform aspects of the present invention.
[0075] Aspects of the present invention are described herein with
reference to flowchart illustrations and/or block diagrams of
methods, apparatus (systems), and computer program products
according to embodiments of the invention. It will be understood
that each block of the flowchart illustrations and/or block
diagrams, and combinations of blocks in the flowchart illustrations
and/or block diagrams, can be implemented by computer readable
program instructions.
[0076] These computer readable program instructions may be provided
to a processor of a general purpose computer, special purpose
computer, or other programmable data processing apparatus to
produce a machine, such that the instructions, which execute via
the processor of the computer or other programmable data processing
apparatus, create means for implementing the functions/acts
specified in the flowchart and/or block diagram block or blocks.
These computer readable program instructions may also be stored in
a computer readable storage medium that can direct a computer, a
programmable data processing apparatus, and/or other devices to
function in a particular manner, such that the computer readable
storage medium having instructions stored therein comprises an
article of manufacture including instructions which implement
aspects of the function/act specified in the flowchart and/or block
diagram block or blocks.
[0077] The computer readable program instructions may also be
loaded onto a computer, other programmable data processing
apparatus, or other device to cause a series of operational steps
to be performed on the computer, other programmable apparatus or
other device to produce a computer implemented process, such that
the instructions which execute on the computer, other programmable
apparatus, or other device implement the functions/acts specified
in the flowchart and/or block diagram block or blocks.
[0078] The flowchart and block diagrams in the Figures illustrate
the architecture, functionality, and operation of possible
implementations of systems, methods, and computer program products
according to various embodiments of the present invention. In this
regard, each block in the flowchart or block diagrams may represent
a module, segment, or portion of instructions, which comprises one
or more executable instructions for implementing the specified
logical function(s). In some alternative implementations, the
functions noted in the block may occur out of the order noted in
the figures. For example, two blocks shown in succession may, in
fact, be executed substantially concurrently, or the blocks may
sometimes be executed in the reverse order, depending upon the
functionality involved. It will also be noted that each block of
the block diagrams and/or flowchart illustration, and combinations
of blocks in the block diagrams and/or flowchart illustration, can
be implemented by special purpose hardware-based systems that
perform the specified functions or acts or carry out combinations
of special purpose hardware and computer instructions.
[0079] It will be understood from the foregoing description that
modifications and changes may be made in various embodiments of the
present invention without departing from its true spirit. The
descriptions in this specification are for purposes of illustration
only and are not to be construed in a limiting sense. The scope of
the present invention is limited only by the language of the
following claims.
* * * * *