linux-kernel - Re: [PATCH] sched/fair: don't NUMA balance for kthreads

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Message-ID: <20200526200015.GG325280@hirez.programming.kicks-ass.net>
Date:   Tue, 26 May 2020 22:00:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     Jens Axboe <axboe@...nel.dk>, Ingo Molnar <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stefano Garzarella <sgarzare@...hat.com>
Subject: Re: [PATCH] sched/fair: don't NUMA balance for kthreads

On Tue, May 26, 2020 at 05:40:06PM +0100, Valentin Schneider wrote:

> > Change the task_tick_numa() check to exclude kernel threads in general,
> > as it doesn't make sense to attempt ot balance for kthreads anyway.
> >
> 
> Does it? (this isn't a rethorical question)
> 
> Suppose a given kthread ends up doing more accesses to some pages
> (via use_mm()) than the other threads that access them, wouldn't it make
> sense to take that into account when it comes to NUMA balancing?

Well, task_tick_numa() tries and farm off a bunch of actual work to
task_work_add(), and there's so very little userspace for a kernel
thread to return to... :-)