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

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Date:	Sat, 04 Apr 2015 10:10:01 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Chris Metcalf <cmetcalf@...hip.com>,
	Frederic Weisbecker <fweisbec@...il.com>
CC:	"Peter Zijlstra (Intel)" <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 2/2] nohz: make nohz_full imply isolcpus

On 04/03/2015 03:20 PM, Chris Metcalf wrote:
> On 04/03/2015 01:42 PM, Frederic Weisbecker wrote:
>> On Fri, Apr 03, 2015 at 12:24:08PM -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.
>>>
>>> Signed-off-by: Chris Metcalf <cmetcalf@...hip.com>
>> I think Rick has a similar patch.
> 
> I didn't see anything relevant in linux-next, though I did see
> cpu_isolated_map
> made into a public symbol in a recent commit by Rik.

I have a few patches in cgroups/for-4.1 as well that
export information about isolated and nohz_full cpus
in /sys/devices/system/cpu/

> Rik, what's the change you're proposing that's similar to this one? Thanks!

I don't have this particular one, and I like it.

I know there are use cases where isolcpus= without
nohz_full= makes sense, but I cannot think of the
reverse.

Acked-by: Rik van Riel <riel@...hat.com>

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