Re: cpusets not cpu hotplug aware
From: Paul Jackson
Date: Tue Aug 22 2006 - 01:12:08 EST
> I think it would be more sensible for the default (i.e. user hasn't
> explicitly configured any cpusets) behavior on a CONFIG_CPUSETS=y
> kernel to match the behavior with a CONFIG_CPUSETS=n kernel.
Basically, in this situation, that would mean that the code that
masks a requested sched_setaffinity cpumask with the tasks
cpus_allowed = cpuset_cpus_allowed(p);
cpus_and(new_mask, new_mask, cpus_allowed);
would not be executed in the case of a kernel configured for cpusets,
when running on a system that wasn't using cpusets.
That's quite doable, and for systems not actually using cpusets, makes
But it makes a bit of discontinuity in the system behaviour when
someone starts using cpusets. If someone makes a cpuset, then suddenly
tasks in the top cpuset start seeing failed sched_setaffinity calls
for any CPU that was brought online after system boot.
If there is some decent way I can get the cpus_allowed of the top
cpuset to track the cpu_online_map, then we avoid this discontinuity
in system behaviour.
I won't rest till it's the best ...
Programmer, Linux Scalability
Paul Jackson <pj@xxxxxxx> 1.925.600.0401
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