Rafael, On Sat, Jul 21, 2012 at 1:14 AM, Rafael J. Wysocki <r...@sisk.pl> 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. > Not sure if you are talking about couple idle series waiting in Len's tree for the merge.
That series actually trying add infrastructure for the hardwares where CPU's need co-ordination which is needed on few ARM hardwares to get into deeper CPU cluster C-states. It is indeed true that without that approach, cpu-hotplug was used to overcome the ordering issue I guess Exynos, Tegra and OMAP are the few ARM architectures I know who has been using the couple cpuidle infrastructure. Regards Santosh Regards Santosh -- 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/
