Invoking input/output (I/O) threads on processors to demote tracks from a cache

• US 9,971,508 B2
• Filed: 06/06/2016
• Issued: 05/15/2018
• Est. Priority Date: 06/06/2016
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Ash, Kevin J., Borlick, Matthew G., Gupta, Lokesh M., Nguyen, Trung N.
• Primary Examiner(s): Gu, Shawn X
• Application Number:
  US15/174,744
• Publication Number:
  US 20170351432A1
• Time in Patent Office: 708 Days
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence
• CPC Class Codes: G06F 12/0817 using directory methods
• CPC Class Codes: G06F 12/084 with a shared cache
• CPC Class Codes: G06F 12/0842 for multiprocessing or multitasking
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 12/0891 using clearing, invalidating or resetting means
• CPC Class Codes: G06F 12/123 with age lists, e.g. queue, most recently used [MRU] list or least recently used [LRU] list
• CPC Class Codes: G06F 12/124 being minimized, e.g. non MRU
• CPC Class Codes: G06F 2212/1024 Latency reduction
• CPC Class Codes: G06F 2212/60 Details of cache memory
• CPC Class Codes: G06F 2212/621 Coherency control relating to peripheral accessing, e.g. from DMA or I/O device
• CPC Class Codes: G06F 3/0605 by facilitating the interaction with a user or administrator
• CPC Class Codes: G06F 3/0653 Monitoring storage devices or systems
• CPC Class Codes: G06F 3/0659 Command handling arrangements, e.g. command buffers, queues, command scheduling
• CPC Class Codes: G06F 3/067 Distributed or networked storage systems, e.g. storage area networks [SAN], network attached storage [NAS]

Abstract

Provided are a computer program product, system, and method for invoking Input/Output (I/O) threads on processors to demote tracks from a cache. An Input/Output (I/O) thread, executed by a processor, processes I/O requests directed to tracks in the storage by accessing the tracks in the cache. After processing at least one I/O request, the I/O thread determines whether a number of free cache segments in the cache is below a free cache segment threshold. The I/O thread processes a demote ready list, indicating tracks eligible to demote from the cache, to demote tracks from the cache in response to determining that the number of free cache segments is below the free cache segment threshold. The I/O thread continues to process I/O requests directed to tracks from the storage stored in the cache after processing the demote ready list to demote tracks in the cache.

Claims

1. A computer program product for managing tracks in a storage in a cache, the computer program product comprising a computer readable storage medium having computer readable program code embodied therein that when executed performs operations, the operations comprising:

processing by an Input/Output (I/O) thread, executed by a processor, I/O requests directed to tracks in the storage by accessing the tracks in the cache;

after processing at least one I/O request, determining by the I/O thread whether a number of free cache segments in the cache is below a free cache segment threshold;

processing, by the I/O thread, a demote ready list, indicating tracks eligible to demote from the cache, to demote tracks from the cache in response to determining that the number of free cache segments is below the free cache segment threshold; and

continuing, by the I/O thread, to process I/O requests directed to tracks from the storage stored in the cache after processing the demote ready list to demote tracks in the cache.

2. The computer program product of claim 1, wherein the I/O thread processes the demote ready list once for every predetermined number of I/O requests processed.

3. The computer program product of claim 2, wherein the I/O thread demotes a number of tracks from the cache equal to a value of the predetermine number of I/O requests when processing the demote ready list.

4. The computer program product of claim 1, wherein the I/O thread processes the demote ready list once for every predetermined number of I/O requests processed during which the I/O thread allocates cache segments in the cache to a track subject to an I/O request.

5. The computer program product of claim 1, wherein the processing of the demote ready list, by the I/O thread, comprises requesting a lock to the demote ready list, wherein the lock serializes access to the demote ready list, and wherein the I/O thread processes the demote ready list to demote a plurality of tracks from the cache in response to receiving the lock to the demote ready list.

6. The computer program product of claim 5, wherein the processing, by the I/O thread of the demote ready list further comprises:

in response to the lock being unavailable, determining whether to wait for the lock to become available based on the number of free cache segments in the cache;

waiting for the lock to become available to obtain the lock to process the demote ready list to demote tracks from the cache in response to determining to wait for the lock to become available; and

returning to processing, by the I/O thread, to process I/O requests in response to determining not to wait for the lock.

7. The computer program product of claim 6, wherein the determining by the I/O thread whether to wait for the lock comprises:

determining to wait for the lock in response to determining that the number of free cache segments is below a wait threshold, wherein the wait threshold is less than the free cache segment threshold; and

determining to not wait for the lock in response to determining that the number of free cache segments is greater than the wait threshold and less than the free cache segment threshold.

8. The computer program product of claim 7, wherein the wait threshold comprises a first wait threshold, wherein the processing, by the I/O thread, the demote ready list to demote tracks comprises:

demoting a first number of tracks from the cache indicated in the demote ready list in response to determining that the number of free cache segments is below a second wait threshold, wherein the second wait threshold is greater than the first wait threshold, wherein both the first wait threshold and second wait threshold are each below the free cache segment threshold; and

demoting a second number of tracks from the cache indicated in the demote ready list in response to determining that the number of free cache segments is more than the second wait threshold, wherein the second wait threshold is greater than the first wait threshold.

9. The computer program product of claim 8, wherein the first wait threshold comprises a first percentage of the free cache segment threshold and wherein the second wait threshold is a second percentage of the free cache segment threshold, wherein the second percentage is greater than the first percentage.

10. The computer program product of claim 1, wherein there is an active cache list and a demote ready list associated with each of a plurality of processor cores, wherein each processor core includes a plurality of independently executing processors to invoke at least one Input/Output (I/O) thread to process the I/O requests and to process the demote ready list in response to determining that the number of free cache segments is below the free cache segment threshold and to invoke a demote scan thread to indicate modified tracks in the demote ready list for the processor core executing the demote scan thread.

11. A system for managing tracks in a storage, comprising:

a plurality of processors;

a memory including a cache storing tracks from the storage;

wherein at least one of the processors executes an Input/Output (I/O) thread to perform;

processing I/O requests directed to tracks in the storage by accessing the tracks in the cache;

after processing at least one I/O request, determining whether a number of free cache segments in the cache is below a free cache segment threshold;

processing a demote ready list, indicating tracks eligible to demote from the cache, to demote tracks from the cache in response to determining that the number of free cache segments is below the free cache segment threshold; and

continuing to process I/O requests directed to tracks from the storage stored in the cache after processing the demote ready list to demote tracks in the cache.

12. The system of claim 11, wherein the I/O thread processes the demote ready list once for every predetermined number of I/O requests processed during which the I/O thread allocates cache segments in the cache to a track subject to an I/O request.

13. The system of claim 11, wherein the processing of the demote ready list, comprises requesting a lock to the demote ready list, wherein the lock serializes access to the demote ready list, and wherein the I/O thread processes the demote ready list to demote a plurality of tracks from the cache in response to receiving the lock to the demote ready list.

14. The system of claim 13, wherein the processing, by the I/O thread, of the demote ready list further comprises:

in response to the lock being unavailable, determining whether to wait for the lock to become available based on the number of free cache segments in the cache;

waiting for the lock to become available to obtain the lock to process the demote ready list to demote tracks from the cache in response to determining to wait for the lock to become available; and

returning to processing to process I/O requests in response to determining not to wait for the lock.

15. The system of claim 14, wherein the determining by the I/O thread whether to wait for the lock comprises:

determining to wait for the lock in response to determining that the number of free cache segments is below a wait threshold, wherein the wait threshold is less than the free cache segment threshold; and

determining to not wait for the lock in response to determining that the number of free cache segments is greater than the wait threshold and less than the free cache segment threshold.

16. The system of claim 15, wherein the wait threshold comprises a first wait threshold, wherein the processing, by the I/O thread, the demote ready list to demote tracks comprises:

demoting a first number of tracks from the cache indicated in the demote ready list in response to determining that the number of free cache segments is below a second wait threshold, wherein the second wait threshold is greater than the first wait threshold, wherein both the first wait threshold and second wait threshold are each below the free cache segment threshold; and

demoting a second number of tracks from the cache indicated in the demote ready list in response to determining that the number of free cache segments is more than the second wait threshold, wherein the second wait threshold is greater than the first wait threshold.

17. The system of claim 11, wherein each of the processors comprises a processor core including an active cache list and a demote ready list, wherein each processor core includes a plurality of independently executing processors to invoke at least one instance of the I/O thread to perform I/O thread operations.

18. A method for managing tracks in a storage in a cache, comprising:

processing, by an Input/Output (I/O) thread, executed by a processor, I/O requests directed to tracks in the storage by accessing the tracks in the cache;

after processing at least one I/O request, determining by the I/O thread whether a number of free cache segments in the cache is below a free cache segment threshold;

processing, by the I/O thread, a demote ready list, indicating tracks eligible to demote from the cache, to demote tracks from the cache in response to determining that the number of free cache segments is below the free cache segment threshold; and

continuing, by the I/O thread, to process I/O requests directed to tracks from the storage stored in the cache after processing the demote ready list to demote tracks in the cache.

19. The method of claim 18, wherein the I/O thread processes the demote ready list once for every predetermined number of I/O requests processed during which the I/O thread allocates cache segments in the cache to a track subject to an I/O request.

20. The method of claim 18, wherein the processing of the demote ready list, by the I/O thread, comprises requesting a lock to the demote ready list, wherein the lock serializes access to the demote ready list, and wherein the I/O thread processes the demote ready list to demote a plurality of tracks from the cache in response to receiving the lock to the demote ready list.

21. The method of claim 20, wherein the processing, by the I/O thread of the demote ready list further comprises:

in response to the lock being unavailable, determining whether to wait for the lock to become available based on the number of free cache segments in the cache;

waiting for the lock to become available to obtain the lock to process the demote ready list to demote tracks from the cache in response to determining to wait for the lock to become available; and

returning to processing, by the I/O thread, to process I/O requests in response to determining not to wait for the lock.

22. The method of claim 21, wherein the determining by the I/O thread whether to wait for the lock comprises:

determining to wait for the lock in response to determining that the number of free cache segments is below a wait threshold, wherein the wait threshold is less than the free cache segment threshold; and

determining to not wait for the lock in response to determining that the number of free cache segments is greater than the wait threshold and less than the free cache segment threshold.

23. The method of claim 22, wherein the wait threshold comprises a first wait threshold, wherein the processing, by the I/O thread, the demote ready list to demote tracks comprises:

demoting a first number of tracks from the cache indicated in the demote ready list in response to determining that the number of free cache segments is below a second wait threshold, wherein the second wait threshold is greater than the first wait threshold, wherein both the first wait threshold and second wait threshold are each below the free cache segment threshold; and

demoting a second number of tracks from the cache indicated in the demote ready list in response to determining that the number of free cache segments is more than the second wait threshold, wherein the second wait threshold is greater than the first wait threshold.