linux-kernel - Re: [RFC PATCH 00/32] Nohz cpusets (was: Nohz Tasks)

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Message-ID: <CALdu-PAd_sr=k1xDPgeFr4Cx2U2x+EZYUz4ykyrNUSCSOb2osQ@mail.gmail.com>
Date:	Sat, 20 Aug 2011 00:45:48 -0700
From:	Paul Menage <paul@...lmenage.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Menage <menage@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephen Hemminger <shemminger@...tta.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 00/32] Nohz cpusets (was: Nohz Tasks)

On Thu, Aug 18, 2011 at 6:25 AM, Frederic Weisbecker <fweisbec@...il.com> wrote:
>>
>> Why not do it unconditionally?  That is, if all the conditions are
>> fulfilled, disable the tick regardless of any cpuset settings.
>
> Because I'm not sure it's a win on every workload. This involves
> some hooks here and there (syscall slow path), IPIs, etc...

I agree with Avi. I'd be inclined to investigate further to see if
there are any important workloads on which it's not a win - and then
add the extra complexity to control it from cpusets if necessary.
Unless there's really a good reason to make it configurable, it's
simpler to make it unconditional.

Paul
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