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Re: [PATCH] sched: Avoid sched domain rebuilding when hotplugging an isolate cpu

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  Re: [PATCH] sched: Avoid sched domain rebuilding when hotplugging an  isolate cpu Peter Zijlstra <peterz@infradead.org> - 2015-07-30 12:40 +0200
    Re: [PATCH] sched: Avoid sched domain rebuilding when hotplugging an  isolate cpu pang.xunlei@zte.com.cn - 2015-07-30 13:20 +0200

#1195895 — Re: [PATCH] sched: Avoid sched domain rebuilding when hotplugging an isolate cpu

On Fri, Jul 17, 2015 at 04:03:45PM +0800, Xunlei Pang wrote:
> From: Xunlei Pang <pang.xunlei@linaro.org>
> 
> The sched domain is always rebuilt when hotplugging an isolate cpu,
> as we can see in partition_sched_domains() with the NULL doms_new,
> current sched domain is destroyed, then rebuilt. Worse still, the
> rebuilding will reset all the parameters of the sched_domain. This
> makes no sense and contradicts the isloate concept.

What parameters? isolcpus should have fairly trivial domains to begin
with.
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#1195913

Hi Peter,

Peter Zijlstra <peterz@infradead.org> wrote 2015-07-30 PM 06:30:37:
> Re: [PATCH] sched: Avoid sched domain rebuilding when hotplugging an
> isolate cpu
> 
> On Fri, Jul 17, 2015 at 04:03:45PM +0800, Xunlei Pang wrote:
> > From: Xunlei Pang <pang.xunlei@linaro.org>
> > 
> > The sched domain is always rebuilt when hotplugging an isolate cpu,
> > as we can see in partition_sched_domains() with the NULL doms_new,
> > current sched domain is destroyed, then rebuilt. Worse still, the
> > rebuilding will reset all the parameters of the sched_domain. This
> > makes no sense and contradicts the isloate concept.
> 
> What parameters? isolcpus should have fairly trivial domains to begin
> with.

I mean the parameters under 
/proc/sys/kernel/sched_domain/cpu<m>/domain<n>,
they will be reset to the default value once sched domain is rebuilt, if 
users have tuned them before, it's very annoying.

So we should avoid the rebuilding if can, like the case in this patch.

Regards,
-Xunlei

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