From: Aaron Tomlin <atomlin@redhat.com>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: Aaron Tomlin <atomlin@atomlin.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
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, 31 Mar 2022 15:33:10 +0100 [thread overview]
Message-ID: <20220331143310.vhsnywx3z7obdycf@ava.usersys.com> (raw)
In-Reply-To: <20220217163205.GA748087@lothringen>
On Thu 2022-02-17 17:32 +0100, Frederic Weisbecker wrote:
> Then I can see two other issues:
>
> 1) Can an interrupt in idle modify the vmstat and thus trigger the need to
> flush it? I believe it's the case and then the problem goes beyond nohz_full
> because if the idle interrupt fired while the tick is stopped and didn't set
> TIF_RESCHED, we go back to sleep without calling quiet_vmstat().
>
> 2) What if we are running task A in kernel mode while the tick is stopped
> (nohz_full). Task A modifies the vmstat and goes to userspace for a long
> while.
>
> Your patch fixes case 1) but not case 2). The problem is that TIMER_DEFERRABLE
> should really be about dynticks-idle only and not dynticks-full. I've always
> been afraid about enforcing that rule though because that would break old
> noise-free setups. But perhaps I should...
Hi Frederic,
Firstly, apologies for the delay.
In reference to case 2:
If I understand correctly, even if TIMER_DEFERRABLE is removed
refresh_cpu_vm_stats() cannot be invoked since the scheduling-clock tick is
disabled i.e. non-deferrable timers are serviced by the tick, no?
So, the only option would be to interrupt the workload - not desirable - or
detect any remaining differentials prior to entering userspace?
Kind regards,
--
Aaron Tomlin
prev parent reply other threads:[~2022-03-31 14:33 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
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 [this message]
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=20220331143310.vhsnywx3z7obdycf@ava.usersys.com \
--to=atomlin@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=mtosatti@redhat.com \
--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).