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

From: Nicolas Pitre
Date: Thu Feb 24 2011 - 15:24:54 EST

On Thu, 24 Feb 2011, Thomas Gleixner wrote:

> On Thu, 24 Feb 2011, Alan Cox wrote:
> > > Anybody who is interested in the latency of cpu hotplug is deluding
> > > himself, also cpu hotplug is _NOT_ a power management feature, so the
> > > rest of your justification just disappeared as well.
> >
> > Actually CPU hotplug is a power management feature on some devices where
> > you need to shutdown one of the cores to enter low power modes.
> Right.
> > Remember we use it as part of the suspend paths and various processors
> > nowdays drop into a suspend to RAM type state on CPU idling.
> The suspend path is using it, but the cpu idle one is hardly using the
> hotplug muck.

Most SMP ARM processors are going to use it soon. Powering down idle
cores provides substantial power saving.

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