Performance loss on SLES 12 SP5 after updating to kernel 4.12.14-122.150 or higher

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Environment

SUSE Linux Enterprise Server 12 SP5

Situation

If a SCSI device is in use and SLES 12 SP5 is updated to kernel 4.12.14-122.150 or later, a significant performance drop may be noticed.

This issue is not expected to affect SLES 15 SPx.

Resolution

A kernel update was released in October 2023, containing a fix.

For SLES 12 SP5 kernel-default 4.12.14-122.179
For kernel-azure: 4.12.14-16.152
For kernel-rt: 4.12.14-10.144

Cause

Kernel 4.12.14-122.150 received the following SCSI fix:

commit da5bd87e56640166a5a4d3053687c02b135bd5bd
Date: Tue Feb 7 08:32:03 2023 -0800
Revert "scsi: core: run queue if SCSI device queue isn't ready
and queue is idle" (git-fixes).

However, the corresponding upstream commit b4fd63f4264 mentions this revert in scsi core should be done in tandem with 2 other commits in blk-mq, which were not present at that time:

ab3cee376 blk-mq: In blk_mq_dispatch_rq_list() "no budget" is a reason to kick
a0823421a blk-mq: Rerun dispatching in the case of budget contention

These have now been added and performance is back to normal.

Status

Top Issue

Disclaimer

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