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

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Message-ID: <alpine.LFD.2.00.1102242115011.2701@localhost6.localdomain6>
Date:	Thu, 24 Feb 2011 21:16:01 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-kernel@...r.kernel.org, linux-hotplug@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>, amit.kucheria@...aro.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH V5 2/2] tracing, perf : add cpu hotplug trace events

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.

Thanks,

	tglx
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