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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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