On Fri, Jul 20, 2012 at 09:44:04PM +0200, Rafael J. Wysocki wrote: > 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.
I don't see how we can get rid of hotplug (or some other state where some processors are completely quiesient) in systems which have CPU clusters with a different number of CPUs in each cluster. (eg 4 and 1 in case of Tegra30). Cheers, Peter. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
