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

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Message-ID: <20150408172424.GC13227@lerouge>
Date:	Wed, 8 Apr 2015 19:24:26 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Chris Metcalf <cmetcalf@...hip.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"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 Wed, Apr 08, 2015 at 11:21:56AM -0400, Chris Metcalf wrote:
> 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?

Please respin. Writing or fixing changelogs is what takes me most time :-)
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