Message-ID: <1438803881.4833.34.camel@j-VirtualBox>
Subject: Re: [RFC PATCH] timer: Improve itimers scalability
From: Jason Low <jason.low2@hp.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Mike Galbraith <umgwanakikbuti@gmail.com>, terry.rudd@hp.com,
        Rik van Riel <riel@redhat.com>, Waiman Long <Waiman.Long@hp.com>,
        Scott J Norton <scott.norton@hp.com>, jason.low2@hp.com
Date: Wed, 05 Aug 2015 12:44:41 -0700
In-Reply-To: <20150805093719.GV25159@twins.programming.kicks-ass.net>
References: <1438734584.2927.15.camel@j-VirtualBox>
	 <20150805093719.GV25159@twins.programming.kicks-ass.net>
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On Wed, 2015-08-05 at 11:37 +0200, Peter Zijlstra wrote:
> On Tue, Aug 04, 2015 at 05:29:44PM -0700, Jason Low wrote:
> 
> > @@ -1137,6 +1148,13 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
> >  	if (READ_ONCE(sig->cputimer.running)) {
> 
> Maybe make that:
> 
> 	if (READ_ONCE(sig->cputimer.running) &&
> 	    !READ_ONCE(sig->cputimer.is_checking_timer)) {

Yes, I think it would be better if the check is done here.

And perhaps the comment can be modified to:

/*
 * Check if thread group timers expired. This is skipped if the cputimer
 * is not running or if another thread in the group is already checking
 * for thread group cputimers.
 */

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