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Bug 1976679

Summary: blk-mq: fix/improve io scheduler batching dispatch
Product: Red Hat Enterprise Linux 8 Reporter: Ming Lei <minlei>
Component: kernelAssignee: Ming Lei <minlei>
kernel sub component: Block Layer QA Contact: ChanghuiZhong <czhong>
Status: CLOSED ERRATA Docs Contact:
Severity: unspecified    
Priority: unspecified CC: acaringi, jmoyer
Version: 8.5Flags: pm-rhel: mirror+
Target Milestone: beta   
Target Release: 8.5   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: kernel-4.18.0-327.el8 Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2021-11-09 19:18:09 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description Ming Lei 2021-06-28 02:24:08 UTC 
Description of problem:

https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/commit/?h=for-5.14/block&id=613471549f366cdf4170b81ce0f99f3867ec4d16

https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/commit/?h=for-5.14/block&id=cb9516be7708a2a18ec0a19fe3a225b5b3bc92c7

One patch is for avoiding to dequeue two many requests, so io merge can be
improved.

Another patch is for fixing batching dispatch, in which hctx->dispatch_busy
is evaluated, but not get updated.
Comment 6 ChanghuiZhong 2021-08-04 08:58:03 UTC 
sanity test passed with kernel-4.18.0-327.el8:
https://beaker.engineering.redhat.com/jobs/5654211
https://beaker.engineering.redhat.com/jobs/5655252

All fix patches has included to kernel tree:
$ git log kernel-4.18.0-327.el8 --oneline --grep=1976679
14b1478fd252 Merge: block: improve batching dispatch and fix discard request merge
377ced4accb4 blk-mq: update hctx->dispatch_busy in case of real scheduler
40aa7107656c block: Do not pull requests from the scheduler when we cannot dispatch them

move to verified + sanityonly
Comment 9 errata-xmlrpc 2021-11-09 19:18:09 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (Moderate: kernel security, bug fix, and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2021:4356