linux-kernel - Re: [PATCH] specific do_timer

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Message-ID: <alpine.LFD.2.02.1202151512420.2794@ionos>
Date:	Wed, 15 Feb 2012 15:16:34 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dimitri Sivanich <sivanich@....com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] specific do_timer_cpu value for nohz off mode

On Tue, 8 Nov 2011, Dimitri Sivanich wrote:
> 
> Allow manual override of the tick_do_timer_cpu.
> 
> While not necessarily harmful, doing jiffies updates on an application cpu
> does cause some extra overhead that HPC benchmarking people notice.  They
> prefer to have OS activity isolated to certain cpus.  They like reproducibility
> of results, and having jiffies updates bouncing around introduces variability.

I really wonder about this changelog. The only case where jiffies
updates bounces around is the NOHZ case. In all other modes (periodic
or highres) the boot cpu gets the do_timer() duty and it's never
assigned to any other cpu.

So what's the point of this exercise? Moving it away from CPU0 for
acedemic reasons or what?

Thanks,

	tglx

 
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