linux-kernel - Re: [RFC] [PATCH] cpuset: fix wrong calculation of relax domain level

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Message-ID: <487F0996.9010904@jp.fujitsu.com>
Date:	Thu, 17 Jul 2008 17:57:58 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	Li Zefan <lizf@...fujitsu.com>
CC:	Paul Jackson <pj@....com>, LKML <linux-kernel@...r.kernel.org>,
	Paul Menage <menage@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lai Jiangshan <laijs@...fujitsu.com>
Subject: Re: [RFC] [PATCH] cpuset: fix wrong calculation of relax domain level

Li Zefan wrote:
> When multiple cpusets are overlapping in their 'cpus' and hence they
> form a single sched domain, the largest sched_relax_domain_level among
> those should be used. But when top_cpuset's sched_load_balance is
> set, its sched_relax_domain_level is used regardless other sub-cpusets'.
> 
> There are several proposals to solve this:
> 
> 1) Travel the cpuset hierarchy to find the largest relax_domain_level
>    in rebuild_sched_domains(). But cpuset avoids hierarchy travelling
>    when top_cpuset.sched_load_balance is set.
> 
> 2) Remember the largest relax_domain_level when we update a cpuset's
>    sched_load_balance, sched_relax_domain_level and cpus. This should
>    work, but seems a bit tricky and a bit ugly. (As this patch shows)
> 
> 3) Don't treat this as a bug, but document this behavior.

I think 1) is correct way.

There was a special short path for the top_cpuset's case, but now it is
disappeared. I think there are no need to treat the top_cpuset as VIP,
so 2) is excessive nurturing.

Thanks,
H.Seto
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