U.S. patent application number 16/985216 was filed with the patent office on 2022-02-10 for providing track access reasons for track accesses resulting in the release of prefetched cache resources for the track.
The applicant listed for this patent is INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Chung Man FUNG, Matthew J. KALOS, Beth Ann PETERSON, Warren Keith STANLEY, Matthew J. WARD.
Application Number | 20220043751 16/985216 |
Document ID | / |
Family ID | |
Filed Date | 2022-02-10 |
United States Patent
Application |
20220043751 |
Kind Code |
A1 |
PETERSON; Beth Ann ; et
al. |
February 10, 2022 |
PROVIDING TRACK ACCESS REASONS FOR TRACK ACCESSES RESULTING IN THE
RELEASE OF PREFETCHED CACHE RESOURCES FOR THE TRACK
Abstract
Provided are a computer program product, system, and method for
providing track access reasons for track accesses resulting in the
release of prefetched cache resources for the track. A first
request for a track is received from a process for which prefetched
cache resources to a cache are held for a second request for the
track that is expected. A track access reason is provided for the
first request specifying a reason for the first request. The
prefetched cache resources are released before the second request
to the track is received. Indication is made in an unexpected
released track list of the track and the track access reason for
the first request.
Inventors: |
PETERSON; Beth Ann; (Tucson,
AZ) ; FUNG; Chung Man; (San Francisco, CA) ;
KALOS; Matthew J.; (Tucson, AZ) ; STANLEY; Warren
Keith; (Loveland, CO) ; WARD; Matthew J.;
(Vail, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INTERNATIONAL BUSINESS MACHINES CORPORATION |
Armonk |
NY |
US |
|
|
Appl. No.: |
16/985216 |
Filed: |
August 4, 2020 |
International
Class: |
G06F 12/0862 20060101
G06F012/0862; G06F 12/0815 20060101 G06F012/0815; G06F 12/0891
20060101 G06F012/0891; G06F 12/02 20060101 G06F012/02; G06F 9/30
20060101 G06F009/30; G06F 13/20 20060101 G06F013/20 |
Claims
1. A computer program product for processing access requests to
tracks in storage cached in a cache, the computer program product
comprising a computer readable storage medium having computer
readable program code embodied therein that is executable to
perform operations, the operations comprising: receiving a first
request for a track from a process for which prefetched cache
resources to the cache are held for a second request for the track
that is expected, wherein a track access reason is provided for the
first request specifying a reason for the first request; releasing
the prefetched cache resources before the second request to the
track is received; and indicating in an unexpected released track
list the track and the track access reason for the first
request.
2. The computer program product of claim 1, wherein the second
request comprises a write to the track in a write set of tracks to
write, wherein the write set including the track is indicated with
the track in the unexpected released track list.
3. The computer program product of claim 1, wherein the operations
further comprise: receiving the second request to the track;
determining that the prefetched cache resources are no longer
available for the second request; searching the unexpected released
track list for the track in response to determining that the
prefetched cache resources are no longer held; and returning the
track access reason for the first request in the unexpected
released track list with a fail for the second request.
4. The computer program product of claim 1, wherein the second
request comprises a first write request received on a first channel
from a host, wherein the host uses the track access reason to
determine whether to retry the first write request as a second
write request to the track on a second channel in response to
receiving a fail to the first write request on the first
channel.
5. The computer program product of claim 4, wherein the first
request for the track that causes the prefetched cache resources to
be released comprises a write request to the track on the second
channel, wherein the track access reason indicates a second channel
write request as a reason for the returned fail to the host,
wherein the host uses the track access reason to determine link
failures on the first channel.
6. The computer program product of claim 1, wherein the process
generating the first request for the track comprises an internal
process in a storage system having the cache, wherein the
operations further comprise: receiving, by a cache manager managing
access to the cache in the storage system, the first request from
the internal process; and sending, by the cache manager, a request
to release the prefetch cache resources and the track access reason
in response to determining that the prefetch cache resources are
held for a write access manager that requested the prefetch cache
resources for a write to the track as part of sequential writes to
a write set of tracks, wherein the write access manager indicates
the track and the track access reason in the unexpected released
track list.
7. The computer program product of claim 1, wherein the process
initiating the first request comprises a copy service forming a
consistency group including the track that causes a quiesce to a
volume including the track, wherein the track access reason
indicates a write miss due to a quiesce of the volume. The computer
program product of claim 1, wherein the process initiating the
first request comprises a read of the track triggered by a write to
a track preceding the track requested by the second request,
wherein the read requires release of the prefetched cache
resources, wherein the operations further comprise: returning fail
to the second request including the track access reason indicating
the prefetched cache resources were released to a read to the
track; and throttling read requests to tracks for which cache
resources are prefetched in response to receiving the track access
reason indicating the prefetched cache resources were released to
the read to the track to avoid read content conflicts to tracks to
write.
9. A system for processing access requests to tracks in storage,
comprising: a processor; a cache to cache tracks in the storage;
and a computer readable storage medium having computer readable
program code embodied therein that when executed by the processor
performs operations, the operations comprising: receiving a first
request for a track from a process for which prefetched cache
resources to the cache are held for a second request for the track
that is expected, wherein a track access reason is provided for the
first request specifying a reason for the first request; releasing
the prefetched cache resources before the second request to the
track is received; and indicating in an unexpected released track
list the track and the track access reason for the first
request.
10. The system of claim 9, wherein the second request comprises a
write to the track in a write set of tracks to write, wherein the
write set including the track is indicated with the track in the
unexpected released track list.
11. The system of claim 9, wherein the operations further comprise:
receiving the second request to the track; determining that the
prefetched cache resources are no longer available for the second
request; searching the unexpected released track list for the track
in response to determining that the prefetched cache resources are
no longer held; and returning the track access reason for the first
request in the unexpected released track list with a fail for the
second request.
12. The system of claim 9, wherein the second request comprises a
first write request received on a first channel from a host,
wherein the host uses the track access reason to determine whether
to retry the first write request as a second write request to the
track on a second channel in response to receiving a fail to the
first write request on the first channel.
13. The system of claim 12, wherein the first request for the track
that causes the prefetched cache resources to be released comprises
a write request to the track on the second channel, wherein the
track access reason indicates a second channel write request as a
reason for the returned fail to the host, wherein the host uses the
track access reason to determine link failures on the first
channel.
14. The system of claim 9, wherein the process generating the first
request for the track comprises an internal process in a storage
system having the cache, wherein the operations further comprise:
receiving, by a cache manager managing access to the cache in the
storage system, the first request from the internal process; and
sending, by the cache manager, a request to release the prefetch
cache resources and the track access reason in response to
determining that the prefetch cache resources are held for a write
access manager that requested the prefetch cache resources for a
write to the track as part of sequential writes to a write set of
tracks, wherein the write access manager indicates the track and
the track access reason in the unexpected released track list.
15. A method for processing access requests to tracks in storage
cached in a cache, comprising: receiving a first request for a
track from a process for which prefetched cache resources to the
cache are held for a second request for the track that is expected,
wherein a track access reason is provided for the first request
specifying a reason for the first request; releasing the prefetched
cache resources before the second request to the track is received;
and indicating in an unexpected released track list the track and
the track access reason for the first request.
16. The method of claim 15, wherein the second request comprises a
write to the track in a write set of tracks to write, wherein the
write set including the track is indicated with the track in the
unexpected released track list.
17. The method of claim 15, further comprising: receiving the
second request to the track; determining that the prefetched cache
resources are no longer available for the second request; searching
the unexpected released track list for the track in response to
determining that the prefetched cache resources are no longer held;
and returning the track access reason for the first request in the
unexpected released track list with a fail for the second
request.
18. The method of claim 15, wherein the second request comprises a
first write request received on a first channel from a host,
wherein the host uses the track access reason to determine whether
to retry the first write request as a second write request to the
track on a second channel in response to receiving a fail to the
first write request on the first channel.
19. The method of claim 18, wherein the first request for the track
that causes the prefetched cache resources to be released comprises
a write request to the track on the second channel, wherein the
track access reason indicates a second channel write request as a
reason for the returned fail to the host, wherein the host uses the
track access reason to determine link failures on the first
channel.
20. The method of claim 15, wherein the process generating the
first request for the track comprises an internal process in a
storage system having the cache, further comprising: receiving, by
a cache manager managing access to the cache in the storage system,
the first request from the internal process; and sending, by the
cache manager, a request to release the prefetch cache resources
and the track access reason in response to determining that the
prefetch cache resources are held for a write access manager that
requested the prefetch cache resources for a write to the track as
part of sequential writes to a write set of tracks, wherein the
write access manager indicates the track and the track access
reason in the unexpected released track list.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a computer program product,
system, and method for providing track access reasons for track
accesses resulting in the release of prefetched cache resources for
the track.
2. Description of the Related Art
[0002] In a storage environment, a host system may first
communicate a read/write request to a connected storage system over
a fast channel, such as a bus interface, or Peripheral Component
Interconnect Express (PCIe) interface. For a read/write request
over the fast channel, which is supposed to complete within a
threshold time, the host system holds the application thread for
the read/write request in a spin loop waiting for the request to
complete. This saves processor time associated with a context swap,
which deactivates the thread and reactivates the thread in response
to an interrupt when a response to the read/write request is
received. If the data for the read/write request sent on the fast
channel is not in cache, then the storage system may fail the
read/write request and the host system may communicate the same
read/write request over a storage area network via a host adaptor,
which is slower than processing the I/O request over the bus, e.g.,
PCIe interface. Communicating the read/write request over the
second channel requires the host system to perform a context switch
from the task handling the read/write request to another task while
waiting for the read/write request to complete. Context switching
is costly because it requires the processor running the task to
clear all registers and L1 and L2 caches for the new task, and then
when completing the new task, reactivate the context switched task
and return the state data to the registers and L1 and L2 caches for
the task that was context switched while waiting for the read/write
request to complete.
[0003] Certain read/write operations need to be completed within a
threshold time, else they are failed. To process a read or write
request, the storage system will have to allocate cache resources,
including resources and segments in cache storage and access track
metadata to process the read or write request. The track metadata
provides information on the format of data and layout of records in
the track that are needed in order to perform reads and writes to
the track. However, the allocation of cache resources, including
accessing of metadata, from the storage comprises a substantial
portion of the latency in processing read/write requests.
[0004] There is a need in the art for improved techniques for
managing host write requests to the cache on the fast channel to
improve the likelihood that prefetched cache resources for tracks
will be available for the expected write requests received on the
fast channel.
SUMMARY
[0005] Provided are a computer program product, system, and method
for providing track access reasons for track accesses resulting in
the release of prefetched cache resources for the track. A first
request for a track is received from a process for which prefetched
cache resources to a cache are held for a second request for the
track that is expected. A track access reason is provided for the
first request specifying a reason for the first request. The
prefetched cache resources are released before the second request
to the track is received. Indication is made in an unexpected
released track list of the track and the track access reason for
the first request.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 illustrates an embodiment of a storage
environment.
[0007] FIG. 2 illustrates an embodiment of write set information
for an established write set.
[0008] FIG. 3 illustrates an embodiment of a track access list
entry in a track access list.
[0009] FIG. 4 illustrates an embodiment of a second channel write
request sent on the second channel to retry a write request that
failed on a first channel.
[0010] FIG. 5 illustrates an embodiment of an unexpected released
track list entry providing a track access reason for an access
request to a track resulting in the release of prefetched cache
resources for the track.
[0011] FIG. 6 illustrates an embodiment of operations to process a
request to access a track for which a track access reason code is
provided.
[0012] FIG. 7 illustrates an embodiment of operations to process a
request to release prefetched cache resources for a track which
includes a track access reason for the request.
[0013] FIG. 8 illustrates an embodiment of operations to process a
write request received on a first channel to write to a track in a
write set.
[0014] FIG. 9 illustrates an embodiment of a computer architecture
used with described embodiments.
DETAILED DESCRIPTION
[0015] Access to a write set may be quiesced if there is an event
that will prevent write access to the tracks for an extended period
of time to allow other processes to access the tracks held for the
write set, such as volume ineligibility due to long busy or
unsupported copy services state or other processes. Quiescing
access to tracks in a write set causes a release of prefetched
cache resources for the tracks in the write set. Releasing the
prefetched cache resources will cause failure for first channel
write requests to retry writing to the tracks in the quiesced write
set if there are no cache resources pre-allocated for these write
requests when the requests are received.
[0016] Prefetching cache resources in advance of the access request
increases the likelihood that write requests sent by the host on a
first fast channel are completed within a required threshold time
for processing access requests on the first channel requiring fast
processing. This keeps the time the host thread is spinning on the
write request task for the write request sent on the bus interface
within an acceptable time threshold. However, if the cache
resources for a requested target track have not been allocated in
advance of the request, it is unlikely the write request can
complete within the threshold time given that the cache resources
will have to be allocated. Failing the write request on the first
channel causes the host to redrive the write request on the second
channel. The processing of the write request on the second channel
allocates the required cache resources when processing the write
request on the second channel.
[0017] Described embodiments provide improvements to computer
technology for processing a fail to an access request to a track
for which prefetched cache resources are not available by providing
track access reasons for processes that requested access to the
track that resulted in the release of the prefetched cache
resources for the track. The host and other processes may use the
track access reasons to determine how to continue processing write
requesting for tracks or to perform other troubleshooting and
debugging operations on why other processes are requesting access
to tracks for which prefetched cache resources are held for fast
first channel writes.
[0018] FIG. 1 illustrates an embodiment of a storage environment in
which a host 100 directs read and write requests to a storage
system 102, also referred to as a storage controller, control unit,
server, to access tracks in volumes configured in storage devices
104 in a disk enclosure 106. The host 100 includes a processor
complex 108 of one or more processor devices and a memory 110
including an operating system 111 executed by the processor complex
108. The host operating system 111 generates read and write
requests to tracks configured in the storage devices 104. The host
100 includes hardware to communicate read and write requests on two
different channels. A "first channel" may comprise a bus interface,
such as a Peripheral Component Interconnect Express (PCIe),
including a bus 112, a bus switch 114 to connect one or more
devices on the bus 112, including the processor complex 108, a
memory system 110, and a bus host adaptor 116 to extend the bus
interface over an external bus interface cable 118 to the storage
system 102. Additional bus interface technology to extend the bus
interface may be utilized, including PCIe extender cables or
components, such as a distributed PCIe switch, to allow PCIe over
Ethernet, such as with the ExpEther technology.
[0019] A "second channel" to connect the host 100 and storage
system 102 may use a network host adaptor 120, connected to the bus
112, that connects to a separate network 122 over which the host
100 and storage system 102 additionally communicate. The first
channel through the bus interface may comprise a faster access
channel than the second channel using the network 122 interface via
the network host adaptor 120.
[0020] The storage system 102 includes a bus interface comprising a
bus 124a, 124b, a bus switch 126 to connect to endpoint devices on
the bus 124a, 124b, and a bus host adaptor 128 to connect to the
external bus interface cable 118 to allow communication over the
bus interface to the host 100 over the first channel. The storage
system 102 includes an Input/Output bay 130 having the bus host
adaptor 128, one or more device adaptors 132 to connect to the
storage devices 104, and one or more network host adaptors 134 to
connect to the network 122 and host systems.
[0021] The storage system 102 includes a processor complex 136 of
one or more processor devices and a memory 138 having a cache 140
to cache tracks accessed by the connected hosts 100. The memory 138
includes a write access manager 142 to manage write requests to the
cache 140, a storage manager 144 to manage access requests from
processes in the hosts 100 and storage system 102 for tracks in the
storage 104, and a cache manager 145 to manage requests to tracks
in the cache 140. The devices 136, 138, 128, 132, and 134 connect
over the bus interface implemented in the bus lanes 124a, 124b and
bus switch 126.
[0022] The write access cache manager 142 prefetches cache
resources, including metadata and other resources, in the cache 140
for a defined write set for which host write requests are expected
on the first channel so that such write requests may be completed
fast with low latency.
[0023] A track may comprise any unit of data configured in the
storage 104, such as a track, Logical Block Address (LBA), etc.,
which is part of a larger grouping of tracks, such as a volume,
logical device, etc.
[0024] The write access manager 142 and/or cache manager 145
maintain cache management information 146 in the memory 138 to
manage read (unmodified) and write (modified) tracks in the cache
140. The cache management information 146 may include a track index
148 providing an index of tracks in the cache 140 to cache control
blocks in a control block directory 150; and a Least Recently Used
(LRU) list 152 for tracks in the cache 140. The control block
directory 150 includes the cache control blocks, where there is one
cache control block for each track in the cache 140 providing
metadata on the track in the cache 140. The track index 148
associates tracks with the cache control blocks providing
information on the tracks in the cache 140. Upon determining that
the cache LRU list 152 is full or has reached a threshold level,
tracks are demoted from the LRU list 152 to make room for more
tracks to stage into the cache 140 from the storage 104.
[0025] The cache management information 146 may further includes
write set information 200 of a write set of tracks established by
the host 100 for tracks to write on the first channel. The write
access manager 140 may prefetch cache resources for tracks in the
write set in advance of receiving write transactions. The host 100
may establish multiple write sets for multiple ranges of tracks for
which track resources will be allocated in anticipation of multiple
streams of sequential write transactions toward the different
ranges of tracks.
[0026] The host operating system 111 may establish a write set 200
for a range of tracks 204 in advance of sending write requests for
sequential write transactions to have the write access manager 142
pre-allocate cache resources for the write set in anticipation of
the sequential write transactions that will likely soon be directed
to those tracks indicated in the write set. These pre-allocated
cache resources reduce the latency of processing the sequential
write requests when they are eventually received. Further, by
allocating cache resources for a limited (fixed number) of a first
subset of tracks within the write set, cache resources are held for
only those tracks most likely to be written as part of a sequential
write stream. Further, the number of tracks for which cache
resources are held is limited to allow those cache resources to be
available for access by other processes in the host operating
system 111 or other connected hosts 100.
[0027] The write access manager 142 maintains an unexpected
released track list 500 having information on track access reasons
for access requests from internal processes 154 or external
processes that resulted in the release of prefetched cache
resources for the track in a write set 200 held for write requests
to tracks in the write set sent on the first channel. The process
154 requesting access to a track may comprise a copy service, such
as copying consistency groups of tracks, a destage/stage operation,
an operation causing a quiesce to the volume including the tracks
in the write set, etc. The unexpected released track list 500 may
have a sufficient number of entries to be large enough to avoid
entries from being overwritten in a short time and to provide
sufficient details on track accesses resulting in the release of
prefetched cache resources to allow in-depth debugging on the cause
of the unexpected release of prefetched cache resources for
tracks.
[0028] A cache resource that is held and accessed for tracks in the
range of tracks 302 may comprise a segment in cache 140 to use for
the track to write, a segment in a non-volatile storage if a copy
of write tracks is to be stored in a non-volatile storage in a same
or different cluster, track metadata for the track, as well as
other types of cache resources needed to process a write
transaction toward the track.
[0029] In certain embodiments, there may be multiple hosts 100 that
connect to the storage system 102 over the first and second
channels to access tracks in the storage devices 104. In such case,
the storage system 102 would have at least one bus host adaptor 128
to connect to the bus interface 118 of each connected host 100 and
one or more network host adaptors 134 to connect to the network
host adaptors 120 on the hosts 100.
[0030] In one embodiment, the bus interfaces 112, 114, 116, 118,
124a, 124b, 126, and 128 may comprise a Peripheral Component
Interconnect Express (PCIe) bus interface technology. In
alternative embodiments, the bus interfaces 112, 114, 116, 118,
124a, 124b, 126, and 128 may utilize suitable bus interface
technology other than PCIe. The bus host adaptors 116 and 128 may
comprise PCIe host adaptors that provide the interface to connect
to the PCIe cable 118. The network 122 may comprise a Storage Area
Network (SAN), a Local Area Network (LAN), a Wide Area Network
(WAN), Fibre Connection (FICON.RTM.), the Internet, an Intranet,
etc., and the network host adaptors 120, 134 provide the network
122 connections between the hosts 100 and storage system 102.
(FICON is a registered trademark of International Business Machines
Corporation throughout the world.
[0031] The storage system 102 may comprise a storage system, also
known as a control unit and storage controller, such as the
International Business Machines Corporation (IBM.RTM.) DS8000.RTM.
and DS8880 storage systems, or storage controllers and storage
systems from other vendors. (IBM and DS8000 are trademarks of
International Business Machines Corporation throughout the world).
The host operating system 111 may comprise an operating system such
as Z Systems Operating System (Z/OS.RTM.) from International
Business Machines Corporation ("IBM") or other operating systems
known in the art. (Z/OS is a registered trademark of IBM throughout
the world).
[0032] The storage devices 104 in the disk enclosure 106 may
comprise different types or classes of storage devices, such as
magnetic hard disk drives, solid state storage device (SSD)
comprised of solid state electronics, EEPROM (Electrically Erasable
Programmable Read-Only Memory), flash memory, flash disk, Random
Access Memory (RAM) drive, storage-class memory (SCM), etc., Phase
Change Memory (PCM), resistive random access memory (RRAM), spin
transfer torque memory (STT-RAM), conductive bridging RAM (CBRAM),
magnetic hard disk drive, optical disk, tape, etc. Volumes in a
storage space may further be configured from an array of devices,
such as Just a Bunch of Disks (JBOD), Direct Access Storage Device
(DASD), Redundant Array of Independent Disks (RAID) array,
virtualization device, etc. Further, the storage devices 104 in the
disk enclosure 106 may comprise heterogeneous storage devices from
different vendors and different types of storage devices, such as a
first type of storage devices, e.g., hard disk drives, that have a
slower data transfer rate than a second type of storage devices,
e.g., SSDs.
[0033] FIG. 2 illustrates an embodiment of an instance of write set
information 200, for an established write set to receive write
requests on the first channel, including a write set identifier
(ID) 202 providing a unique identifier of a write set; a range of
tracks 204 to which sequential write transactions on the first
channel are expected and for which cache resources should be
accessed in advance of the sequential write transactions; a track
access list 300 indicating for each track in the range of tracks
204 whether the cache resources are being held for the track and
whether the track was written since receiving the establish write
set 200i; and a prefetch cursor 206 indicating a track in the range
of tracks 302 from which cache resources should start being
allocated for sequential write transactions in the write set
202.
[0034] In certain embodiments, the prefetch cursor 206 may be set
during regular processing to point at the track the write access
manager 142 anticipates the host 100 to be writing (if actively
writing) or to be writing next (if not actively writing). The
prefetch cursor 206 points to where the write access manager 142
determines the host 100 is in their processing.
[0035] FIG. 3 illustrates an embodiment of a track access list
entry 300i in the track access list 300 indicating a track
identifier (ID) 302; a cache resources held flag 304 indicating
whether cache resources are being held for the track 302 and a
track written flag 306 indicating whether the track 302 was written
since the write set 202 was established.
[0036] FIG. 4 illustrates an embodiment of a second channel write
request 400 received on the second channel from the host 100, and
includes: a write operation code 402; a define extent range 404 of
a subset of tracks in a write set 408 to which the following one or
more sequential write transactions 406 will be directed; and a
retry on first channel flag 410 indicating whether the write
transactions 406 in the second channel write request 400 will be
subsequently retried on the faster first channel.
[0037] FIG. 5 illustrates an embodiment of an entry 500i in the
unexpected released track list 500 and includes: a track 502
identifying the accessed track for which prefetched cache resources
were released; a volume 504 including the track; a write set 506 in
which the track is included for first channel writes; and a track
access reason 508 indicating a reason the process 154 or another
process accessed the track. A track access reason may indicate a
quiesce of the volume, a read or write to the track on the second
channel, a read to the track, etc. Track access reasons can include
any reasons that can assist the host 100, process or a user to
debug fails of writes on the first channel or allow the host 100 to
adjust operations to reduce the cause of the track access reasons
resulting in the unexpected release of prefetched case
resources.
[0038] FIG. 6 illustrates an embodiment of operations performed by
the cache manager 145 to process a request to a track, such as a
first request, from a process 154 or other external process with a
track access reason code. The track access reason code may be
maintained in a task control block (TCB) or other task management
operation implementing the process 154. Upon receiving (at block
600) the access request (first request) to the track, if (at block
602) there are no cache resources prefetched for the track to
access, such as being held for a write request on the first
channel, or second request, then the access request to the track in
cache 140 is processed (at block 604). If (at block 602) there are
prefetched cache resources held for the track, then the cache
manager 145 sends (at block 606) a request to the write access
manager 142 to release the prefetched cache resources for the track
with the track access reason the process 154 provides for the first
request. Upon receiving (at block 608) confirmation from the write
access manager 142 that the prefetched cache resources are
released, control proceeds to block 604 to allow the first request
from the process 154 to complete.
[0039] FIG. 7 illustrates an embodiment of operations performed by
the write access manager 142 to process a request from the cache
manager 145 to release prefetched cache resources with a track
access reason for the request. Upon receiving (at block 700) the
request to release prefetched cache resources, the write access
manager 142 releases (at block 702) the prefetched cache resources
for the requested track. The track access list entry 300, for the
requested track in the track access list 300 is updated (at block
704) to indicate no cache resources are held 304. The unexpected
released track list 500 is updated (at block 706) to include an
entry 500.sub.i, indicating the requested track 502, volume 504 of
track, the write set 506 including the track, and the track access
reason code 508 indicating a reason for the request for the
track.
[0040] With the embodiments of FIGS. 6 and 7, the write access
manager 142 has the capability to track reasons that other
processes 154 requested a track in a write set for which prefetched
cache resources were held and caused those prefetched cache
resources to be released, resulting in a fail of a subsequent write
to the track expected on the fast first channel. The host 100 or a
user may use the track access reasons 508, provided for the release
of prefetched cache resources that would have caused first channel
write requests to fail, to debug and troubleshoot the reason for
the unexpected release of prefetched cache resources before the
expected writes are received on the first channel.
[0041] FIG. 8 illustrates an embodiment of operations performed by
the write access manager 142 to process a write to a track in a
write set received on the first channel, a second request with
respect to the first request from the process 154. Upon receiving
(at block 800) the write request on the first channel, the write
access manager 142 determines (at block 802) whether prefetched
cache resources are available for the track to write. If so, the
write request on the first channel is processed (at block 804). If
(at block 802) there are no prefetched cache resources available
for the write, then the write access manager 142 searches (at block
806) the unexpected released track list 500 for an entry 500.sub.i,
having the requested track 502 and the write set 504 including the
track. If (at block 808) no entry 500.sub.i, is found in the list
500, then fail is returned (at block 810) to the host without any
track access reason 508 to assist the host or other process in
addressing or troubleshooting the fail. If (at block 808) there is
an entry 500.sub.i, for the track and write set in the list, then
the write access manager 142 returns (at block 812) fail with the
track access reason 508 in the located entry 500.sub.i.
[0042] In one embodiment, the process resulting in the release of
the prefetched cache resources may comprise a host 100 request on
the second channel for the track. In such case, the track access
reason code may indicate second channel track access. For instance,
if there are errors on the first channel link that cause a host
timeout, then the host may retry writing the track over the second
channel link. In such case, the write access manager 142 may
indicate the track access reason code as a second channel write.
Analysis of storage system 102 dumps may reveal that the host
retried a write on the second channel that failed and the first
channel link may need to be diagnosed as a possible cause of this
failure.
[0043] The track access reason code may also indicate that the
unexpected release of prefetched cache resources is due to a
quiesce of the volume including the track caused by a copy service
forming consistency groups of tracks, including the requested
track. This information will allow the host or other user to
diagnose the cause of a subsequent failure of a write on the first
channel as resulting from copy services.
[0044] In certain processes, reads may closely follow writes on the
first channel to read data, such as logged data. If the reads
follow too closely to the writes, then contention for track access
can cause the release of prefetched cache resources for tracks that
are held for expected first channel writes. The host 100 upon
receiving failures to first channel write requests including the
track access reason code indicating a read of the track, may then
throttle the reads to avoid contention with the expected writes to
the tracks.
[0045] In one embodiment, where the second channel comprises a
Fibre Connection (FICON.RTM.) link, which is the International
Business Machines Corporation's (IBM) proprietary name for the ANSI
FC-SB-3 Single-Byte Command Code Sets-3 Mapping Protocol for Fibre
Channel (FC), the first channel comprises the IBM zHyperLink, and
the host operating system 111 comprises Z/OS.RTM., then the host
100 may retry a failed zHyperLink (first channel) write via the
FICON interface (second channel).
[0046] The present invention may be implemented as 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.
[0047] 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.
[0048] 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.
[0049] 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 Java, 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] The computational components of FIG. 1, including the host
100 and storage system 102 may be implemented in one or more
computer systems, such as the computer system 902 shown in FIG. 9.
Computer system/server 902 may be described in the general context
of computer system executable instructions, such as program
modules, being executed by a computer system. Generally, program
modules may include routines, programs, objects, components, logic,
data structures, and so on that perform particular tasks or
implement particular abstract data types. Computer system/server
902 may be practiced in distributed cloud computing environments
where tasks are performed by remote processing devices that are
linked through a communications network. In a distributed cloud
computing environment, program modules may be located in both local
and remote computer system storage media including memory storage
devices.
[0055] As shown in FIG. 9, the computer system/server 902 is shown
in the form of a general-purpose computing device. The components
of computer system/server 902 may include, but are not limited to,
one or more processors or processing units 904, a system memory
906, and a bus 908 that couples various system components including
system memory 906 to processor 904. Bus 908 represents one or more
of any of several types of bus structures, including a memory bus
or memory controller, a peripheral bus, an accelerated graphics
port, and a processor or local bus using any of a variety of bus
architectures. By way of example, and not limitation, such
architectures include Industry Standard Architecture (ISA) bus,
Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus,
Video Electronics Standards Association (VESA) local bus, and
Peripheral Component Interconnects (PCI) bus.
[0056] Computer system/server 902 typically includes a variety of
computer system readable media. Such media may be any available
media that is accessible by computer system/server 902, and it
includes both volatile and non-volatile media, removable and
non-removable media.
[0057] System memory 906 can include computer system readable media
in the form of volatile memory, such as random access memory (RAM)
910 and/or cache memory 912. Computer system/server 902 may further
include other removable/non-removable, volatile/non-volatile
computer system storage media. By way of example only, storage
system 913 can be provided for reading from and writing to a
non-removable, non-volatile magnetic media (not shown and typically
called a "hard drive"). Although not shown, a magnetic disk drive
for reading from and writing to a removable, non-volatile magnetic
disk (e.g., a "floppy disk"), and an optical disk drive for reading
from or writing to a removable, non-volatile optical disk such as a
CD-ROM, DVD-ROM or other optical media can be provided. In such
instances, each can be connected to bus 908 by one or more data
media interfaces. As will be further depicted and described below,
memory 906 may include at least one program product having a set
(e.g., at least one) of program modules that are configured to
carry out the functions of embodiments of the invention.
[0058] Program/utility 914, having a set (at least one) of program
modules 916, may be stored in memory 906 by way of example, and not
limitation, as well as an operating system, one or more application
programs, other program modules, and program data. Each of the
operating system, one or more application programs, other program
modules, and program data or some combination thereof, may include
an implementation of a networking environment. The components of
the computer 902 may be implemented as program modules 916 which
generally carry out the functions and/or methodologies of
embodiments of the invention as described herein. The systems of
FIG. 1 may be implemented in one or more computer systems 902,
where if they are implemented in multiple computer systems 902,
then the computer systems may communicate over a network.
[0059] Computer system/server 902 may also communicate with one or
more external devices 918 such as a keyboard, a pointing device, a
display 920, etc.; one or more devices that enable a user to
interact with computer system/server 902; and/or any devices (e.g.,
network card, modem, etc.) that enable computer system/server 902
to communicate with one or more other computing devices. Such
communication can occur via Input/Output (I/O) interfaces 922.
Still yet, computer system/server 902 can communicate with one or
more networks such as a local area network (LAN), a general wide
area network (WAN), and/or a public network (e.g., the Internet)
via network adapter 924. As depicted, network adapter 924
communicates with the other components of computer system/server
902 via bus 908. It should be understood that although not shown,
other hardware and/or software components could be used in
conjunction with computer system/server 902. Examples, include, but
are not limited to: microcode, device drivers, redundant processing
units, external disk drive arrays, RAID systems, tape drives, and
data archival storage systems, etc.
[0060] The terms "an embodiment", "embodiment", "embodiments", "the
embodiment", "the embodiments", "one or more embodiments", "some
embodiments", and "one embodiment" mean "one or more (but not all)
embodiments of the present invention(s)" unless expressly specified
otherwise.
[0061] The terms "including", "comprising", "having" and variations
thereof mean "including but not limited to", unless expressly
specified otherwise.
[0062] The enumerated listing of items does not imply that any or
all of the items are mutually exclusive, unless expressly specified
otherwise.
[0063] The terms "a", "an" and "the" mean "one or more", unless
expressly specified otherwise.
[0064] Devices that are in communication with each other need not
be in continuous communication with each other, unless expressly
specified otherwise. In addition, devices that are in communication
with each other may communicate directly or indirectly through one
or more intermediaries.
[0065] A description of an embodiment with several components in
communication with each other does not imply that all such
components are required. On the contrary a variety of optional
components are described to illustrate the wide variety of possible
embodiments of the present invention.
[0066] When a single device or article is described herein, it will
be readily apparent that more than one device/article (whether or
not they cooperate) may be used in place of a single
device/article. Similarly, where more than one device or article is
described herein (whether or not they cooperate), it will be
readily apparent that a single device/article may be used in place
of the more than one device or article or a different number of
devices/articles may be used instead of the shown number of devices
or programs. The functionality and/or the features of a device may
be alternatively embodied by one or more other devices which are
not explicitly described as having such functionality/features.
Thus, other embodiments of the present invention need not include
the device itself.
[0067] The foregoing description of various embodiments of the
invention has been presented for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed. Many modifications and
variations are possible in light of the above teaching. It is
intended that the scope of the invention be limited not by this
detailed description, but rather by the claims appended hereto. The
above specification, examples and data provide a complete
description of the manufacture and use of the composition of the
invention. Since many embodiments of the invention can be made
without departing from the spirit and scope of the invention, the
invention resides in the claims herein after appended.
* * * * *