* Peter Zijlstra [off-list ref] [2009-09-15 14:11:41]:

On Tue, 2009-09-15 at 17:36 +0530, Gautham R Shenoy wrote:

quoted

This patchset contains the offline state driver implemented for
pSeries. For pSeries, we define three available_hotplug_states. They are:

        online: The processor is online.

        offline: 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.

        inactive: This cedes the vCPU to the hypervisor with a cede latency
        specifier value 2.
        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.

Any feedback on the patchset will be immensely valuable.

I still think its a layering violation... its the hypervisor manager
that should be bothered in what state an off-lined cpu is in. 

From a design standpoint where we stand today is

1. A cede indicates that the CPU is no longer needed and can be
reassigned (remember we do dedicated CPU partitions in power)
2. What this patch is trying to do is to say "We don't need the
CPU, but please don't reassign, put it to sleep"

We work the same way with the hypervisor, that applications work with
the OS today, by providing madvise and other hints.

-- 
	Balbir