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

From: Peter Zijlstra
Date: Thu Feb 24 2011 - 15:48:34 EST

On Thu, 2011-02-24 at 15:40 -0500, 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.

Not much of it,

> We're talking
> about cores completely going down with power pulled beneath them and
> eventually rebooted dynamically here.

I think you can get away with actually pulling the power and re-initing
the cpu to idle from the idle path and the rest of the kernel not

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