Messages in this thread | | | Date | Tue, 1 Oct 2013 20:07:50 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] hotplug: Optimize {get,put}_online_cpus() |
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On 10/01, Peter Zijlstra wrote: > > On Tue, Oct 01, 2013 at 07:45:08PM +0200, Oleg Nesterov wrote: > > > > I tend to agree with Srivatsa... Without a strong reason it would be better > > to preserve the current logic: "some time after" should not be after the > > next CPU_DOWN/UP*. But I won't argue too much. > > Nah, I think breaking it is the right thing :-)
I don't really agree but I won't argue ;)
> > But note that you do not strictly need this change. Just kill cpuhp_waitcount, > > then we can change cpu_hotplug_begin/end to use xxx_enter/exit we discuss in > > another thread, this should likely "join" all synchronize_sched's. > > That would still be 4k * sync_sched() == terribly long.
No? the next xxx_enter() avoids sync_sched() if rcu callback is still pending. Unless __cpufreq_remove_dev_finish() is "too slow" of course.
> > Or split cpu_hotplug_begin() into 2 helpers which handle FAST -> SLOW and > > SLOW -> BLOCK transitions, then move the first "FAST -> SLOW" handler outside > > of for_each_online_cpu(). > > Right, that's more messy but would work if we cannot teach cpufreq (and > possibly others) to not rely on state you shouldn't rely on anyway.
Yes,
> I tihnk the only guarnatee POST_DEAD should have is that it should be > called before UP_PREPARE of the same cpu ;-) Nothing more, nothing less.
See above... This makes POST_DEAD really "special" compared to other CPU_* events.
And again. Something like a global lock taken by CPU_DOWN_PREPARE and released by POST_DEAD or DOWN_FAILED does not look "too wrong" to me.
But I leave this to you and Srivatsa.
Oleg.
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