Subject: Re: [PATCH v2 0/2] cpu: pseries: Offline state framework.

From: Benjamin Herrenschmidt <[email-masked]>
Date: Thu, 24 Sep 2009 18:38:27 +1000

On Thu, 2009-09-24 at 09:51 +0200, Peter Zijlstra wrote:
> > I don't quite follow your logic here. This is useful for more than just
> > hypervisors. For example, take the HV out of the picture for a moment
> > and imagine that the HW has the ability to offline CPU in various power
> > levels, with varying latencies to bring them back.
> 
> cpu-hotplug is an utter slow path, anybody saying latency and hotplug in
> the same sentence doesn't seem to grasp either or both concepts.

Let's forget about latency then. Let's imagine I want to set a CPU
offline to save power, vs. setting it offline -and- opening the back
door of the machine to actually physically replace it :-)

In any case, I don't see the added feature as being problematic, and
not such a "layering violation" as you seem to imply it is. It's a
convenient way to atomically take the CPU out -and- convey some
information about the "intent" to the hypervisor, and I really fail
to see why you have so strong objections about it.

Ben.