From: Jason Low <jason.low2@hp.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Galbraith <umgwanakikbuti@gmail.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Rik van Riel <riel@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
Scott Norton <scott.norton@hp.com>,
Aswin Chandramouleeswaran <aswin@hp.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] sched, timer: Use atomics for thread_group_cputimer to improve scalability
Date: Mon, 02 Mar 2015 13:19:32 -0800 [thread overview]
Message-ID: <1425331172.5304.50.camel@j-VirtualBox> (raw)
In-Reply-To: <20150302194033.GA27914@redhat.com>
On Mon, 2015-03-02 at 20:40 +0100, Oleg Nesterov wrote:
> Well, I forgot everything about this code, but let me ask anyway ;)
>
> On 03/02, Jason Low wrote:
> > @@ -222,13 +239,10 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
> > * it.
> > */
> > thread_group_cputime(tsk, &sum);
> > - raw_spin_lock_irqsave(&cputimer->lock, flags);
> > - cputimer->running = 1;
> > - update_gt_cputime(&cputimer->cputime, &sum);
> > - } else
> > - raw_spin_lock_irqsave(&cputimer->lock, flags);
> > - *times = cputimer->cputime;
> > - raw_spin_unlock_irqrestore(&cputimer->lock, flags);
> > + update_gt_cputime(cputimer, &sum);
> > + ACCESS_ONCE(cputimer->running) = 1;
>
> WRITE_ONCE() looks better...
Okay, I can update that.
> but it is not clear to me why do we need it
> at all.
Peter suggested it here as we would now be updating the running field
without the lock:
https://lkml.org/lkml/2015/1/23/641
next prev parent reply other threads:[~2015-03-02 21:19 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-02 18:42 [PATCH v2] sched, timer: Use atomics for thread_group_cputimer to improve scalability Jason Low
2015-03-02 19:03 ` Linus Torvalds
2015-03-02 21:49 ` Jason Low
2015-03-19 17:21 ` Jason Low
2015-03-19 17:59 ` Linus Torvalds
2015-03-19 20:14 ` Jason Low
2015-03-02 19:40 ` Oleg Nesterov
2015-03-02 19:43 ` Oleg Nesterov
2015-03-02 21:16 ` Jason Low
2015-03-02 21:44 ` Linus Torvalds
2015-03-02 22:43 ` Jason Low
2015-03-05 15:20 ` Frederic Weisbecker
2015-03-05 20:02 ` Jason Low
2015-03-02 21:19 ` Jason Low [this message]
2015-03-05 15:35 ` Frederic Weisbecker
2015-03-05 15:56 ` Paul E. McKenney
2015-03-05 16:00 ` Frederic Weisbecker
2015-03-05 16:16 ` Paul E. McKenney
2015-03-06 0:06 ` Jason Low
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