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

[Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>]

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