Re: cpusets not cpu hotplug aware

From: Paul Jackson
Date: Tue Aug 22 2006 - 01:12:08 EST

Nathan wrote:
> 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
good sense.

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
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at