From: Aaron Tomlin <atomlin@atomlin.com>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Frederic Weisbecker <frederic@kernel.org>,
Christoph Lameter <cl@linux.com>,
tglx@linutronix.de, mingo@kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Phil Auld <pauld@redhat.com>
Subject: Re: [RFC PATCH] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too
Date: Thu, 24 Feb 2022 13:00:14 +0000 [thread overview]
Message-ID: <20220224130014.rmhtx3xlepybuxn2@ava.usersys.com> (raw)
In-Reply-To: <Yhd5olg9CjXSAf2s@fuller.cnet>
On Thu 2022-02-24 09:27 -0300, Marcelo Tosatti wrote:
> But Aaron, vmstat_shepherd should be ensuring that per-CPU vmstat_update
> work are queued, if the per-CPU vmstat are out of sync.
Hi Marcelo,
Yes, I agree; albeit, as far as I understand, in the context of a nohz_full
CPU that has its scheduling-clock tick stopped, we cannot rely on any
deferred work.
The purpose of my patch was to prevent a nohz_full CPU from entering idle
state when CPU-specific vmstat data is non-zero.
> And:
>
> static void
> trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
> {
> if (!is_timers_nohz_active())
> return;
>
> /*
> * TODO: This wants some optimizing similar to the code below, but we
> * will do that when we switch from push to pull for deferrable timers.
> */
> if (timer->flags & TIMER_DEFERRABLE) {
> if (tick_nohz_full_cpu(base->cpu))
> wake_up_nohz_cpu(base->cpu);
> return;
> }
>
> * @TIMER_DEFERRABLE: A deferrable timer will work normally when the
> * system is busy, but will not cause a CPU to come out of idle just
> * to service it; instead, the timer will be serviced when the CPU
> * eventually wakes up with a subsequent non-deferrable timer.
>
> You'd want that vmstat_update to execute regardless of whether there are
> armed non-deferrable timers.
>
> Should fix both 1 and 2 AFAICS.
>
If I understand correctly, you are suggesting to switch to a non-deferred
timer for such work when the scheduling-clock tick is stopped? Indeed, it
would address both scenarios yet I'm not sure we'd want that due to the
performance impact which might be more than negligible.
Kind regards,
--
Aaron Tomlin
next prev parent reply other threads:[~2022-02-24 13:00 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-03 21:43 [RFC PATCH] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too Aaron Tomlin
2022-02-03 22:22 ` Phil Auld
2022-02-16 14:34 ` Aaron Tomlin
2022-02-16 21:20 ` Phil Auld
2022-02-17 12:57 ` Frederic Weisbecker
2022-02-17 14:45 ` Aaron Tomlin
2022-02-17 12:47 ` Frederic Weisbecker
2022-02-17 14:26 ` Aaron Tomlin
2022-02-17 16:32 ` Frederic Weisbecker
2022-02-18 12:54 ` Aaron Tomlin
2022-02-19 15:46 ` Aaron Tomlin
2022-02-24 12:27 ` Marcelo Tosatti
2022-02-24 12:30 ` Marcelo Tosatti
2022-02-24 13:01 ` Aaron Tomlin
2022-02-24 12:37 ` Marcelo Tosatti
2022-02-24 13:00 ` Aaron Tomlin [this message]
2022-02-24 13:14 ` Marcelo Tosatti
2022-02-24 13:28 ` Aaron Tomlin
2022-02-24 13:40 ` Marcelo Tosatti
2022-02-24 13:44 ` Aaron Tomlin
2022-03-31 14:33 ` Aaron Tomlin
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