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Date: Mon, 4 Oct 2021 10:39:29 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com> Cc: Intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, Tvrtko Ursulin <tvrtko.ursulin@...el.com>, Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org> Subject: Re: [RFC 1/6] sched: Add nice value change notifier On Mon, Oct 04, 2021 at 09:12:37AM +0100, Tvrtko Ursulin wrote: > On 01/10/2021 16:48, Peter Zijlstra wrote: > > Hmm? That's for normalize_rt_tasks() only, right? Just don't have it > > call the notifier in that special case (that's a magic sysrq thing > > anyway). > > You mean my talk about tasklist_lock? No, it is also on the syscall part I > am interested in as well. Call chain looks like this: Urgh, I alwys miss that because it lives outside of sched.. :/ > sys_setpriority() > { > ... > rcu_read_lock(); > read_lock(&tasklist_lock); > ... > set_one_prio() > set_user_nice() > { > ... > task_rq_lock(); > -> my notifier from this RFC [1] > task_rq_unlock(); > -> I can move the notifier here for _some_ improvement [2] > } > ... > read_unlock(&tasklist_lock); > rcu_read_unlock(); > } > > So this RFC had the notifier call chain at [1], which I understood was the > thing you initially pointed was horrible, being under a scheduler lock. > > I can trivially move it to [2] but that still leaves it under the tasklist > lock. I don't have a good feel how much better that would be. If not good > enough then I will look for a smarter solution with less opportunity for > global impact. So task_list lock is pretty terrible and effectively unbound already (just create more tasks etc..) so adding a notifier call there shouldn't really make it much worse.
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