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 15:54:49 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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 09:35 -0500, Rik van Riel wrote:
> On 03/02/2015 07:44 AM, Mike Galbraith wrote:
> > On Mon, 2015-03-02 at 10:09 +0100, Peter Zijlstra wrote:
> >> On Thu, Feb 26, 2015 at 12:12:31PM -0500, Rik van Riel wrote:
> >>> Subject: cpusets,isolcpus: add file to show isolated cpus in cpuset
> >>>
> >>> The previous patch makes it so the code skips over isolcpus when
> >>> building scheduler load balancing domains. This makes it hard to
> >>> see for a user which of the CPUs in a cpuset are participating in
> >>> load balancing, and which ones are isolated cpus.
> >>>
> >>> Add a cpuset.isolcpus file with info on which cpus in a cpuset are
> >>> isolated CPUs.
> >>>
> >>> This file is read-only for now. In the future we could extend things
> >>> so isolcpus can be changed at run time, for the root (system wide)
> >>> cpuset only.
> >>>
> >>> Acked-by: David Rientjes <rientjes@...gle.com>
> >>> 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: David Rientjes <rientjes@...gle.com>
> >>> Cc: Mike Galbraith <umgwanakikbuti@...il.com>
> >>> Cc: cgroups@...r.kernel.org
> >>> Signed-off-by: Rik van Riel <riel@...hat.com>
> >>
> >> So let me start off by saying I hate isolcpus ;-)
> >>
> >> Let me further state that I had hopes we could extend cpusets to
> >> natively provide the functionality isolcpus has, and kill isolcpus.
> > 
> > +1
> > 
> > That's where nohz_full goop belongs too.
> 
> Except nohz_full and isolcpus are very much global attributes of
> each CPU, so I am not sure whether it would make sense to allow
> configuration of this attribute anywhere other than the root
> cpuset.

They're attributes of exclusive sets, which excludes the root set.  It'd
be kinda hard to have the root set be both ticked and tickless :)

	-Mike


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