Date: Tue, 7 May 2013 01:03:33 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Olivier Langlois <olivier@trillion01.com>
Cc: Ingo Molnar <mingo@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Chris Metcalf <cmetcalf@tilera.com>, Christoph Lameter <cl@linux.com>,
        Geoff Levand <geoff@infradead.org>,
        Gilad Ben Yossef <gilad@benyossef.com>,
        Hakan Akkan <hakanakkan@gmail.com>, Kevin Hilman <khilman@linaro.org>,
        Li Zhong <zhong@linux.vnet.ibm.com>, Oleg Nesterov <oleg@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 2/3] posix_timers: Defer per process timer stop after
 timers processing
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On Tue, Apr 30, 2013 at 01:51:58PM -0400, Olivier Langlois wrote:
> 
> > 
> > > Maybe the condition around the posix_cpu_timer_schedule() block inside
> > > cpu_timer_fire() could even be a good candidate for 'unlikely'
> > > qualifier.
> > 
> > Well, cpu_timer_fire() is probably not a fast path. So helping branch
> > prediction there probably won't have much measurable effect in practice.
> > 
> Frederic, I'm totally sure that you are right on the measurable effect.
> When I did propose the 'unlikely' qualifier, please note, that I also
> had a documentary purpose in mind.
> 
> Would you have searched the 'likely' path that does
> posix_cpu_timer_schedule() when you did modify the code if the
> 'unlikely' tag would have been present?

It's indeed sometimes a good indicator.

But here it's in the end of a batch of conditional blocks, so it sort
of already suggests itself as an unlikely event.

But if you feel the comment can be improved, don't hesitate to send a patch.


> 
> Greetings,
> Olivier
> 
> 
> 
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