Messages in this thread | | | Date | Mon, 04 Jun 2012 18:23:20 -0700 | From | Arjan van de Ven <> | Subject | Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi |
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On 6/4/2012 5:40 PM, Rusty Russell wrote: > On Mon, 04 Jun 2012 22:33:21 +0200, Peter Zijlstra <peterz@infradead.org> wrote: >> On Mon, 2012-06-04 at 22:11 +0200, Thomas Gleixner wrote: >> >>> I understand what you are trying to do, though I completely disagree >>> with the solution. >>> >>> The main problem of the current hotplug code is that it is an all or >>> nothing approach. You have to tear down the whole thing completely >>> instead of just taking it out of the usable set of cpus. >>> >>> I'm working on a proper state machine driven online/offline sequence, >>> where you can put the cpu into an intermediate state which avoids >>> bringing it down completely. This is enough to get the full >>> powersaving benefits w/o having to go through all the synchronization >>> states of a full online/offline. That will shorten the onlining time >>> of an previously offlined cpu to almost nothing. >>> >>> I really want to avoid adding more bandaids to the hotplug code before >>> we have sorted out the existing horror. >> >> Its far worse.. you shouldn't _ever_ care about hotplug latency unless >> you've got absolutely braindead hardware. We all now ARM has been >> particularly creative here, but is Intel now trying to trump ARM at >> stupid? > > I disagree. Deactivating a cpu for power saving is halfway to hotplug > anyway. I'd rather unify the two cases, where we can specify how dead a > CPU should be, than have individual archs and boards do random hacks.
well on PC's there really is no difference at least; idle equals "all power removed" already there.
but I can see that on some other architectures, that lack idle that deep, there can be a real difference.
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