RE: Random high CPU utilization in blk-mq with the none scheduler

Dexuan Cui
2021-12-14T03:09:39Z

> From: Ming Lei <ming.lei@redhat.com>
> Sent: Monday, December 13, 2021 4:53 PM
> ...
> The single hw queue may be the root cause of your issue, and there
> is only single run_work, which can be touched by all CPUs(~200) almost, so
> cache
> ping-pong could be very serious.
>
> Jens patch may improve it more or less, please test it.
>
> Thanks,
> Ming

I replied to Jens's email with the test result before your email. :-)

Jen's patch does help in the absence of dc5fc361d891
("block: attempt direct issue of plug list").

BTW, the throughput in the case of dm_mod.dm_mq_queue_depth=256
is slightly better than the case of dm_mod.dm_mq_queue_depth=2048 with
Jen's patch or dc5fc361d891.