linux-kernel - Re: [PATCH] blk-mq: add module parameter to not run block kworker on isolated CPUs

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Message-ID: <ZSilDBknf2yqDKNB@fedora>
Date:   Fri, 13 Oct 2023 10:01:48 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Juri Lelli <juri.lelli@...hat.com>,
        Andrew Theurer <atheurer@...hat.com>,
        Joe Mario <jmario@...hat.com>,
        Sebastian Jug <sejug@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>, ming.lei@...hat.com
Subject: Re: [PATCH] blk-mq: add module parameter to not run block kworker on
 isolated CPUs

Hi Tejun,

On Thu, Oct 12, 2023 at 09:55:55AM -1000, Tejun Heo wrote:
> Hello,
> 
> On Wed, Oct 11, 2023 at 08:39:05AM +0800, Ming Lei wrote:
> > I appreciate that any specific suggestions about dealing with isolated CPUs
> > generically for bound WQ can be shared.
> 
> Oh, all I meant was whether we can at least collect this into or at least
> adjacent to the existing housekeeping / isolcpu parameters. Let's say
> there's someone who really wants to isolated some CPUs, how would they find
> out the different parameters if they're scattered across different
> subsystems?

AFAIK, the issue is reported on RH Openshift environment and it is real use
case, some of CPUs are isolated for some dedicated tasks(such as network polling,
...) by passing "isolcpus=managed_irq nohz_full".

But blk-mq still queue kworker on these isolated CPUs, and cause very long
latency in nvme IO workloads. Joe should know the story much more then me.


Thanks,
Ming