From: Marcelo Tosatti <mtosatti@redhat.com>
To: Aaron Tomlin <atomlin@atomlin.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 10:14:58 -0300 [thread overview]
Message-ID: <YheE0joXm53Hxn4J@fuller.cnet> (raw)
In-Reply-To: <20220224130014.rmhtx3xlepybuxn2@ava.usersys.com>
On Thu, Feb 24, 2022 at 01:00:14PM +0000, Aaron Tomlin wrote:
> 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.
Aaron,
If the per-CPU vmstat_update is limited to happen once per second, that
shouldnt be a significant performance impact?
next prev parent reply other threads:[~2022-02-24 13:15 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
2022-02-24 13:14 ` Marcelo Tosatti [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YheE0joXm53Hxn4J@fuller.cnet \
--to=mtosatti@redhat.com \
--cc=atomlin@atomlin.com \
--cc=cl@linux.com \
--cc=frederic@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mingo@kernel.org \
--cc=pauld@redhat.com \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).