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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>