linux-kernel - Re: [RFC PATCH 00/13] nohz: Use sysidle detection to let the timekeeper sleep

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Date:	Wed, 18 Dec 2013 10:04:43 +0800
From:	Alex Shi <alex.shi@...aro.org>
To:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	John Stultz <john.stultz@...aro.org>,
	Kevin Hilman <khilman@...aro.org>
Subject: Re: [RFC PATCH 00/13] nohz: Use sysidle detection to let the timekeeper
 sleep

On 12/18/2013 06:51 AM, Frederic Weisbecker wrote:
> So this is what this series brings, more details following:
> 
> * Some code, naming and whitespace cleanups
> 
> * Allow all CPUs outside the nohz_full range to handle the timekeeping
>   duty, not just CPU 0. Balancing the timekeeping duty should improve
>   powersavings.

If the system just has one nohz_full cpu running, it will need another
cpu to do timerkeeper job. Then the system roughly needs 2 cpu living.
>From powersaving POV, that is not good compare to normal nohz idle.
> 
> * Let the timekeeper (including CPU 0) sleep when its duty is
>   handed over to another CPU
> 
> * Allow timekeeper to sleep when all full dynticks CPUs are sleeping
>   (plug nohz to RCU sysidle detection)

Thanks Fredic!
It is much better on powersaving POV compare to current nohz_full. :)
> 
> * Wake up timekeeper with an IPI when full dynticks CPUs exit sysidle
>   state
> 
> * Wake up CPU 0 when a secondary timekeeper is offlined so that its
>   duty gets migrated


-- 
Thanks
    Alex
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