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

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Date:	Wed, 8 Apr 2015 19:27:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Chris Metcalf <cmetcalf@...hip.com>
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 Wed, Apr 08, 2015 at 11:21:56AM -0400, Chris Metcalf wrote:
> 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.

But you're doing the reverse! You're setting nohz_full for isolcpus, not
limiting the nohz_full mask to isolcpus.

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