linux-kernel - Re: [PATCH v2 2/2] nohz: make nohz

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Message-ID: <55254794.4070503@ezchip.com>
Date:	Wed, 8 Apr 2015 11:21:56 -0400
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] nohz: make nohz_full imply isolcpus

On 04/08/2015 10:26 AM, Peter Zijlstra wrote:
> On Wed, Apr 08, 2015 at 10:04:43AM -0400, Chris Metcalf wrote:
>> On 04/08/2015 05:41 AM, Peter Zijlstra wrote:
>>> On Mon, Apr 06, 2015 at 02:16:45PM -0400, cmetcalf@...hip.com wrote:
>>>> From: Chris Metcalf <cmetcalf@...hip.com>
>>>>
>>>> It's not clear that nohz_full is useful without isolcpus also
>>>> set, since otherwise the scheduler has to run periodically to
>>>> try to determine whether to steal work from other cores.
>>> So the Changelog and the patch don't seem to agree with one another.
>>>
>>> The Changelog states that nohz_full should depend on isolcpus.
>> The git commit message says "make nohz_full imply isolcpus".
>> That's consistent with the code.
> Well, but then the Changelog doesn't make any sense.

Apparently the body of the commit message isn't as clear as it might be :-)

It does say the same thing, though, basically that if nohz_full DOESN'T
imply isolcpus, that's a bad thing.  I'm happy to reword the text to avoid
the double negative and say:

   nohz_full is only useful with isolcpus also set, since otherwise the
   scheduler has to run periodically to try to determine whether to steal
   work from other cores.

Frederic, do you want me to respin the patch, or can you just update
the text of the commit message as above?

-- 
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com

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