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    SubjectRe: [PATCH 0/3] cpu: idle state framework for offline CPUs.
    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.

    >
    > > 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 ?

    >
    > Thanks,
    > Shaohua

    --
    Thanks and Regards
    gautham


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