linux-kernel - Re: [PATCH v4 2/2] cpusets,isolcpus: add file to show isolated cpus in cpuset

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Date:	Mon, 02 Mar 2015 18:35:38 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Zefan Li <lizefan@...wei.com>, linux-kernel@...r.kernel.org,
	Clark Williams <williams@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	David Rientjes <rientjes@...gle.com>, cgroups@...r.kernel.org
Subject: Re: [PATCH v4 2/2] cpusets,isolcpus: add file to show isolated cpus
 in cpuset

On Mon, 2015-03-02 at 11:09 -0500, Tejun Heo wrote:
> On Mon, Mar 02, 2015 at 05:02:57PM +0100, Mike Galbraith wrote:
> > Well, those are the only ones we can do anything about.  Dirt simple
> > diddling of the workqueue default mask as sched domains are
> > added/removed should do it I think.  Automatically moving any existing
> > unbound worker away from isolated cores at the same time would be a
> > bonus, most important is that no new threads sneak in.
> 
> Worker pools are immutable once created and configuraiton changes are
> achieved by creating new pools and draining old ones but at any rate
> making it follow config changes is almost trivial.  Figuring out
> configuration policy might take a bit of effort tho.  Can you point me
> to what specific configuration it should be following?

For cpusets, an exclusive set should become taboo to unbound workers
when load balancing is turned off.  The user making sched domains go
away is a not so subtle hint that he wants no random interference, as he
is trying to assume full responsibility for task placement therein.

In my trees, I let the user turn rt cpupri/push/pull off as well, as
that further reduces jitter.

	-Mike

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