Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait ornmi

[Peter Zijlstra]

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?
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