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...
next prev parent 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
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