* Shaohua Li <shaohua...@intel.com> [2009-08-06 09:58:55]: > 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.
Hi Shaohua, Notification to userspace and an opportunity to react to the situation is certainly better to manage as compared to under-the-cover reduction in capacity. We are already doing something to this effect in virtualized guests where VCPU entitlement and assignment can be changed by the hypervisor based on resource constraints. This framework with notification and determinism will help manage cpu capacity better. I agree with Peter that scheduler approach is better, but it is not deterministic. This is simpler and cleaner alternative to keep the complexity in userspace and provide only framework to control/notify kernel. > > 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. Yes that is what we would expect, but the deepest sleep state may be restricted by BIOS or other system level parameters. This was the main objection to Venki's deepest sleep state for offline cpus patch. There could be higher level policy that restricts the deepest level C-states for various reasons. This framework is to provide an opportunity to adhere to the policy with userspace inputs. This framework also helps to choose different states in a virtualized system. --Vaidy _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
