On Thu, Aug 06, 2009 at 09:48:44PM +0800, Gautham R Shenoy wrote: > Hi Shaohua, > > On Thu, Aug 06, 2009 at 09:58:55AM +0800, Shaohua Li wrote: > > Hi, > > > > On Wed, Aug 05, 2009 at 10:25:53PM +0800, Gautham R Shenoy wrote: > > > In this patch-series, we propose to extend the CPU-Hotplug infrastructure > > > and allow the system administrator to choose the desired state the CPU > > > should > > > go to when it is offlined. We think this approach addresses the concerns > > > about > > > determinism as well as transparency, since CPU-Hotplug already provides > > > notification mechanism which the userspace can listen to for any change > > > in the configuration and correspondingly readjust any previously set > > > cpu-affinities. > > Peter dislikes any approach (including cpuhotplug) which breaks userspace > > policy, > > even userspace can get a notification. > > I think Peter's problem was more to do with the kernel offlining the CPUs > behind the scenes, right ? > > We don't do that in this patch series. The option to offline the CPUs is > very much with the admin. The patch-series only provides the interface > that helps the admin choose the state the CPU must reside in when it > goes offline. but the goal is to use cpu offline to save power, right? So we still have Peter's problem. > > > Also, approaches such as [1] can make use of this > > > extended infrastructure instead of putting the CPU to an arbitrary C-state > > > when it is offlined, thereby providing the system administrator a rope to > > > hang > > > himself with should he feel the need to do so. > > I didn't see the reason why administrator needs to know which state offline > > cpu > > should stay. Don't know about powerpc side, but in x86 side, it appears > > deepest > > C-state is already preferred. > > We can still provide a sane default value based on what states are > available and what the BIOS limits us to. Thus we can still use the > idle-state-offline patch that Venki posted sometime ago, right ? My original concern about Venki's patch is the C-state limition, but Venki thought if CPU has the limition, CPU should disable specific C-state, so this isn't a problem. I had no objection about the infrastructure itself, but just wonder why we need it.
Thanks, Shaohua _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev