From: Valentin Schneider <firstname.lastname@example.org> To: Peter Zijlstra <email@example.com> Cc: Jens Axboe <firstname.lastname@example.org>, Ingo Molnar <email@example.com>, "linux-kernel\@vger.kernel.org" <firstname.lastname@example.org>, Stefano Garzarella <email@example.com> Subject: Re: [PATCH] sched/fair: don't NUMA balance for kthreads Date: Wed, 27 May 2020 00:42:40 +0100 Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <20200526200015.GG325280@hirez.programming.kicks-ass.net> On 26/05/20 21:00, Peter Zijlstra wrote: > 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... :-) Err, true... I did say pipe dreams! I had only really taken note of the exit / return to userspace callbacks, but I see io_uring has its own task_work_run() calls, which (I think) explains how we can end up with a kthread actually running task_numa_work(). I'm also thinking we really don't want that task_numa_work() to be left hanging on the task_work list, because that self-looping thing will not play nice to whatever else has been queued (which AFAICT shouldn't happen under normal conditions, i.e. !kthreads).
prev parent reply index Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-05-26 15:38 Jens Axboe 2020-05-26 16:37 ` [tip: sched/urgent] sched/fair: Don't " tip-bot2 for Jens Axboe 2020-05-26 16:40 ` [PATCH] sched/fair: don't " Valentin Schneider 2020-05-26 20:00 ` Peter Zijlstra 2020-05-26 23:42 ` Valentin Schneider [this message]
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