Re: [PATCH V5 2/2] tracing, perf : add cpu hotplug trace events

From: Thomas Gleixner
Date: Thu Feb 24 2011 - 15:50:23 EST

On Thu, 24 Feb 2011, Nicolas Pitre wrote:

> On Thu, 24 Feb 2011, Peter Zijlstra wrote:
> > On Thu, 2011-02-24 at 15:24 -0500, Nicolas Pitre wrote:
> >
> > > Most SMP ARM processors are going to use it soon. Powering down idle
> > > cores provides substantial power saving.
> >
> > And why can't regular idle paths be used? CPU hotplug is a massively
> > expensive operation.
> The idle path assumes that the CPU state is preserved. We're talking
> about cores completely going down with power pulled beneath them and
> eventually rebooted dynamically here.

That's the equivalent of physical hotplug, but we still have all the
memory state around, so it is possible from idle, when we have the
full isolation features in place.


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