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

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Message-ID: <20191209231743.GA19256@dread.disaster.area>
Date:   Tue, 10 Dec 2019 10:17:43 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Phil Auld <pauld@...hat.com>, 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>, Tejun Heo <tj@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: single aio thread is migrated crazily by scheduler

On Mon, Dec 09, 2019 at 10:21:22PM +0530, Srikar Dronamraju wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 44123b4d14e8..efd740aafa17 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2664,7 +2664,12 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
>   */
>  int wake_up_process(struct task_struct *p)
>  {
> -	return try_to_wake_up(p, TASK_NORMAL, 0);
> +	int wake_flags = 0;
> +
> +	if (is_per_cpu_kthread(p))
> +		wake_flags = WF_KTHREAD;
> +
> +	return try_to_wake_up(p, TASK_NORMAL, WF_KTHREAD);

This is buggy. It always sets WF_KTHREAD, even for non-kernel
processes. I think you meant:

	return try_to_wake_up(p, TASK_NORMAL, wake_flags);

I suspect this bug invalidates the test results presented, too...

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