Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCHSET] workqueue: reimplement CPU hotplug to keep idle workers | Date | Fri, 20 Jul 2012 21:44:04 +0200 |
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On Friday, July 20, 2012, Tejun Heo wrote: > Hello, > > On Fri, Jul 20, 2012 at 08:22:30PM +0200, Peter Zijlstra wrote: > > I really think people who use hotplug at high frequencies are on drugs > > and doing it wrong. > > I don't know. It does make some sense. It's not like we have any > other mechanism to keep some processors completely quiesient, which > could make a noticeable difference from powersaving POV compared to > mostly idle. Rafael, can you please chime in and explain how / where > / how freqeuntly / etc CPU hotplug is used for powersaving?
Well, there are use cases I'm not really familiar with.
Pretty much the only use case I'm sufficiently familiar with is suspend/hibernate where we unplug all of the nonboot CPUs at one point.
The other use cases, which I don't really think are entirely valid, are on some ARM platforms where CPUs are unplugged instead of being put into C-states or equivalent (because we don't have a good mechanism for handling multiprocessor C-states; there's a set of patches for that waiting for the merge window in the Len's tree). I'm hoping to get rid of those use cases in future entirely.
Thanks, Rafael
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