linux-kernel - Re: [PATCH 2/3] posix_timers: Defer per process timer stop after timers processing

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Date:	Tue, 30 Apr 2013 13:51:58 -0400
From:	Olivier Langlois <olivier@...llion01.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Kevin Hilman <khilman@...aro.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/3] posix_timers: Defer per process timer stop after
 timers processing


> 
> > 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?

Greetings,
Olivier



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