[SRU] [B/C] [PATCH 0/2] Fix for LP: #1815733

Kai-Heng Feng kai.heng.feng at canonical.com
Wed Apr 24 10:23:28 UTC 2019

BugLink: https://bugs.launchpad.net/bugs/1815733

Quote from the bug description:
This behavior affects production systems, because every change uevent
triggers udev to change settings prior to udev rules. Some software, for
example arcconf (tool for managing adaptec HBA adapters) triggers
uevents for every block device. So, every call to arcconf utility
results in latency spike.

Avoid unnecessary queue freeze in either one of the case:
 - the queue depth is about to be set to the same value, or 
 - scheduler is "none" and is about to be set to "none" again.

The user confirm these two patches works.

[Regression Potential]
Low. The fix has been in Disco for a while, should be safe to backport
to older releases.

Aleksei Zakharov (2):
  block: avoid setting nr_requests to current value
  block: avoid setting none scheduler if it's already none

 block/blk-mq.c   | 3 +++
 block/elevator.c | 3 +++
 2 files changed, 6 insertions(+)


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