linux-kernel - Re: [PATCH 1/2] cpusets,isolcpus: exclude isolcpus from load balancing in cpusets

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Message-ID: <alpine.DEB.2.10.1502241810420.19547@chino.kir.corp.google.com>
Date:	Tue, 24 Feb 2015 18:10:56 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Rik van Riel <riel@...hat.com>
cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Clark Williams <williams@...hat.com>,
	Li Zefan <lizefan@...wei.com>, Ingo Molnar <mingo@...hat.com>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	cgroups@...r.kernel.org
Subject: Re: [PATCH 1/2] cpusets,isolcpus: exclude isolcpus from load balancing
 in cpusets

On Mon, 23 Feb 2015, riel@...hat.com wrote:

> From: Rik van Riel <riel@...hat.com>
> 
> Ensure that cpus specified with the isolcpus= boot commandline
> option stay outside of the load balancing in the kernel scheduler.
> 
> Operations like load balancing can introduce unwanted latencies,
> which is exactly what the isolcpus= commandline is there to prevent.
> 
> Previously, simply creating a new cpuset, without even touching the
> cpuset.cpus field inside the new cpuset, would undo the effects of
> isolcpus=, by creating a scheduler domain spanning the whole system,
> and setting up load balancing inside that domain. The cpuset root
> cpuset.cpus file is read-only, so there was not even a way to undo
> that effect.
> 
> This does not impact the majority of cpusets users, since isolcpus=
> is a fairly specialized feature used for realtime purposes.
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Clark Williams <williams@...hat.com>
> Cc: Li Zefan <lizefan@...wei.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Luiz Capitulino <lcapitulino@...hat.com>
> Cc: cgroups@...r.kernel.org
> Signed-off-by: Rik van Riel <riel@...hat.com>

Tested-by: David Rientjes <rientjes@...gle.com>
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