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Message-ID: <1422036451.2436.10.camel@j-VirtualBox>
Subject: Re: [RFC PATCH] sched, timer: Use atomics for thread_group_cputimer
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From: Jason Low <jason.low2@hp.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Mike Galbraith <umgwanakikbuti@gmail.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Scott J Norton <scott.norton@hp.com>, Chegu Vinod <chegu_vinod@hp.com>,
        Aswin Chandramouleeswaran <aswin@hp.com>, linux-kernel@vger.kernel.org,
        jason.low2@hp.com
Date: Fri, 23 Jan 2015 10:07:31 -0800
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References: <1421983913.4432.22.camel@j-VirtualBox>
	 <20150123093341.GK2896@worktop.programming.kicks-ass.net>
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On Fri, 2015-01-23 at 10:33 +0100, Peter Zijlstra wrote:
> > +		.running = ATOMIC_INIT(0),                              \
> > +	atomic_t running;
> > +		atomic_set(&sig->cputimer.running, 1);
> > @@ -174,7 +174,7 @@ static inline bool cputimer_running(struct task_struct *tsk)
> > +	if (!atomic_read(&cputimer->running))
> > +	if (!atomic_read(&cputimer->running)) {
> > +		atomic_set(&cputimer->running, 1);
> > +	if (atomic_read(&tsk->signal->cputimer.running))
> > +	atomic_set(&cputimer->running, 0);
> > +	if (atomic_read(&sig->cputimer.running)) {
> > +	if (atomic_read(&tsk->signal->cputimer.running))
> 
> That doesn't really need an atomic_t.

Yeah, I was wondering about that, and made it atomic since we had:

    raw_spin_lock_irqsave(&cputimer->lock, flags);
    cputimer->running = 0;
    raw_spin_unlock_irqrestore(&cputimer->lock, flags);

in stop_process_timers().