All of lore.kernel.org
 help / color / mirror / Atom feed
From: Frederic Weisbecker <frederic@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 2/6] posix-cpu-timers: Don't start process wide cputime counter if timer is disabled
Date: Wed, 9 Jun 2021 14:18:32 +0200	[thread overview]
Message-ID: <20210609121832.GE104634@lothringen> (raw)
In-Reply-To: <20210604113159.26177-3-frederic@kernel.org>

On Fri, Jun 04, 2021 at 01:31:55PM +0200, Frederic Weisbecker wrote:
> If timer_settime() is called with a 0 expiration on a timer that is
> already disabled, the process wide cputime counter will be started
> and won't ever get a chance to be stopped by stop_process_timer() since
> no timer is actually armed to be processed.
> 
> This process wide counter might bring some performance hit due to the
> concurrent atomic additions at the thread group scope.
> 
> The following snippet is enough to trigger the issue.
> 
> 	void trigger_process_counter(void)
> 	{
> 		timer_t id;
> 		struct itimerspec val = { };
> 
> 		timer_create(CLOCK_PROCESS_CPUTIME_ID, NULL, &id);
> 		timer_settime(id, TIMER_ABSTIME, &val, NULL);
> 		timer_delete(id);
> 	}
> 
> So make sure we don't needlessly start it.
> 
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Eric W. Biederman <ebiederm@xmission.com>

No Fixes tag for this one. It has been there since year 1 AG.

I suspect it's the same for most other commits in the series, checking...

  reply	other threads:[~2021-06-09 12:18 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-04 11:31 [PATCH 0/6] posix-cpu-timers: Bunch of fixes Frederic Weisbecker
2021-06-04 11:31 ` [PATCH 1/6] posix-cpu-timers: Fix rearm racing against process tick Frederic Weisbecker
2021-06-09 11:54   ` Frederic Weisbecker
2021-06-11 11:49     ` Peter Zijlstra
2021-06-11 12:37       ` Frederic Weisbecker
2021-06-04 11:31 ` [PATCH 2/6] posix-cpu-timers: Don't start process wide cputime counter if timer is disabled Frederic Weisbecker
2021-06-09 12:18   ` Frederic Weisbecker [this message]
2021-06-10 10:24     ` Frederic Weisbecker
2021-06-16  8:51   ` Peter Zijlstra
2021-06-16 10:51     ` Frederic Weisbecker
2021-06-16 11:26       ` Peter Zijlstra
2021-06-16 11:50         ` Peter Zijlstra
2021-06-04 11:31 ` [PATCH 3/6] posix-cpu-timers: Force next_expiration recalc after timer deletion Frederic Weisbecker
2021-06-16  9:16   ` Peter Zijlstra
2021-06-04 11:31 ` [PATCH 4/6] posix-cpu-timers: Force next_expiration recalc after timer reset Frederic Weisbecker
2021-06-16  9:23   ` Peter Zijlstra
2021-06-16 11:21     ` Frederic Weisbecker
2021-06-16 11:33       ` Peter Zijlstra
2021-06-04 11:31 ` [PATCH 5/6] posix-cpu-timers: Force next expiration recalc after early timer firing Frederic Weisbecker
2021-06-16  9:42   ` Peter Zijlstra
2021-06-16 11:59     ` Frederic Weisbecker
2021-06-16 13:23       ` Peter Zijlstra
2021-06-16 14:53         ` Frederic Weisbecker
2021-06-04 11:31 ` [PATCH 6/6] posix-cpu-timers: Force next expiration recalc after itimer reset Frederic Weisbecker

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=20210609121832.GE104634@lothringen \
    --to=frederic@kernel.org \
    --cc=ebiederm@xmission.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=oleg@redhat.com \
    --cc=peterz@infradead.org \
    --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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.