linux-kernel - Re: single aio thread is migrated crazily by scheduler

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Message-ID: <20191118211804.GW4614@dread.disaster.area>
Date:   Tue, 19 Nov 2019 08:18:04 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Ming Lei <ming.lei@...hat.com>, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jeff Moyer <jmoyer@...hat.com>,
        Dave Chinner <dchinner@...hat.com>,
        Eric Sandeen <sandeen@...hat.com>,
        Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>
Subject: Re: single aio thread is migrated crazily by scheduler

On Mon, Nov 18, 2019 at 09:56:33PM +0530, Srikar Dronamraju wrote:
> * Dave Chinner <david@...morbit.com> [2019-11-16 10:40:05]:
> 
> > On Fri, Nov 15, 2019 at 03:08:43PM +0800, Ming Lei wrote:
> > > On Fri, Nov 15, 2019 at 03:56:34PM +1100, Dave Chinner wrote:
> > > > On Fri, Nov 15, 2019 at 09:08:24AM +0800, Ming Lei wrote:
> > > I can reproduce the issue with 4k block size on another RH system, and
> > > the login info of that system has been shared to you in RH BZ.
> > > 
> > > 1)
> > 
> > Almost all the fio task migrations are coming from migration/X
> > kernel threads. i.e it's the scheduler active balancing that is
> > causing the fio thread to bounce around.
> > 
> 
> Can we try with the below patch.

That makes things much, much worse.

$ sudo trace-cmd show |grep fio |wc -l
4701
$

Even when not running the fio workload (i.e. the system is largely
idle and I'm just doing admin tasks like setting up for test runs),
the number of task migrations that occur goes up significantly.

-Dave.
-- 
Dave Chinner
david@...morbit.com