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    SubjectRe: [PATCH v2 0/2] cpu: pseries: Offline state framework.
    On Wed 2009-09-02 07:33:31, Peter Zijlstra wrote:
    > On Fri, 2009-08-28 at 15:30 +0530, Gautham R Shenoy wrote:
    > > Hi,
    > >
    > > This is the version 2 of the patch series to provide a cpu-offline framework
    > > that enables the administrators choose the state the offline CPU must be put
    > > into when multiple such states are exposed by the underlying architecture.
    > >
    > > Version 1 of the Patch can be found here:
    > > http://lkml.org/lkml/2009/8/6/236
    > >
    > > The patch-series exposes the following sysfs tunables to
    > > allow the system-adminstrator to choose the state of a CPU:
    > >
    > > To query the available hotplug states, one needs to read the sysfs tunable:
    > > /sys/devices/system/cpu/cpu<number>/available_hotplug_states
    > > To query or set the current state, on needs to read/write the sysfs tunable:
    > > /sys/devices/system/cpu/cpu<number>/current_states
    > >
    > > The patchset ensures that the writes to the "current_state" sysfs file are
    > > serialized against the writes to the "online" file.
    > >
    > > This patchset also contains the offline state driver implemented for
    > > pSeries. For pSeries, we define three available_hotplug_states. They are:
    > >
    > > online: The processor is online.
    > >
    > > deallocate: This is the the default behaviour when the cpu is offlined
    > > even in the absense of this driver. The CPU would call make an
    > > rtas_stop_self() call and hand over the CPU back to the resource pool,
    > > thereby effectively deallocating that vCPU from the LPAR.
    > > NOTE: This would result in a configuration change to the LPAR
    > > which is visible to the outside world.
    > >
    > > deactivate: This cedes the vCPU to the hypervisor which
    > > in turn can put the vCPU time to the best use.
    > > NOTE: This option DOES NOT result in a configuration change
    > > and the vCPU would be still entitled to the LPAR to which it earlier
    > > belong to.
    > >
    > > Awaiting your feedback.
    >
    > I'm still thinking this is a bad idea.
    >
    > The OS should only know about online/offline.
    >
    > Use the hypervisor interface to deal with the cpu once its offline.
    >
    > That is, I think this interface you propose is a layering violation.

    Agreed. Plus having interface like 'go to this state during offliine'
    then 'go offline' is strange/stupid. For hypervisor case, you might
    want to change 'state' of cpu that is already offline.
    Pavel

    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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