Re: exclusive cpusets broken with cpu hotplug

[Nick Piggin <nickpiggin@yahoo.com.au>]

Paul Jackson wrote:
> Robin wrote:
> 
>>Could this be as simple as a CPU_UP_PREPARE or CPU_DOWN_PREPARE
>>removing all the cpu_exclusive cpusets and a CPU_UP_CANCELLED,
>>CPU_DOWN_CANCELLED, CPU_ONLINE, CPU_DEAD going through and
>>partitioning all the cpu_exclusive cpusets.
> 
> 
> Perhaps.
> 
> The somewhat related problems, in my book, are:
> 
>  1) I don't know how to tell what sched domains/groups a system has, nor
>     how to tell my customers how to see what sched domains they have, and

I don't know if you want customers do know what domains they have. I think
you should avoid having explicit control over sched-domains in your cpusets
completely, and just have the cpusets create partitioned domains whenever
it can.

> 
>  2) I suspect that Mr. Cpusets doesn't understand sched domains and that
>     Mr. Sched Domain doesn't understand cpusets, and that we've ended
>     up with some inscrutable and likely unsuitable interactions between
>     the two as a result, which in particular don't result in cpusets
>     driving the sched domain configuration in the desired ways for some
>     of the less trivial configs.
> 
>     Well ... at least the first suspcicion above is a near certainty ;).

cpusets is the only thing that messes with sched-domains (excluding the
isolcpus -- that seems to require a small change to partition_sched_domains,
but forget that for now).

And so you should know what partitioning to build at any point when asked.
So we could have a call to cpusets at the end of arch_init_sched_domains,
which asks for the domains to be partitioned, no?

-- 
SUSE Labs, Novell Inc.
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