Re: Possible race between CPU hotplug and perf_pmu_migrate_context

[Peter Zijlstra]

On Fri, Sep 05, 2014 at 10:31:49AM -0700, Linus Torvalds wrote:
> So quite frankly, the whole perf_pmu_migrate_context() thing looks
> completely and fundamentally broken.

Yes, agreed. We can go play very nasty games, but fundamentally agreed.

> Or even just say: "if somebody takes down a CPU with existing uncore
> events, those events are now effectively dead". Don't try to migrate
> them, don't try to create new events on another CPU, just let it go.
> The CPU is down, the events are inactive.
> 
> Keep it simple. Not the current completely broken thing that clearly
> doesn't honor the actual real rules for "event->ctx". Because the
> current rules are effectively that event->ctx is a constant over the
> whole lifetime of the event. Agreed?

I like this best, I've never really been a supporter of hotplug games. 
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