Date: Thu, 12 May 2005 09:16:37 -0700
From: Tony Lindgren <tony@atomide.com>
To: Lee Revell <rlrevell@joe-job.com>
Cc: vatsa@in.ibm.com, Nick Piggin <nickpiggin@yahoo.com.au>,
       schwidefsky@de.ibm.com, jdike@addtoit.com, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org
Subject: Re: [RFC] (How to) Let idle CPUs sleep
Message-ID: <20050512161636.GA15653@atomide.com>
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* Lee Revell <rlrevell@joe-job.com> [050512 09:05]:
> On Thu, 2005-05-12 at 14:16 +0530, Srivatsa Vaddagiri wrote:
> > On Wed, May 11, 2005 at 11:03:49AM -0700, Tony Lindgren wrote:
> > > Sorry to jump in late. For embedded stuff we should be able to skip
> > > ticks until something _really_ happens, like an interrupt.
> > > 
> > > So we need to be able to skip ticks several seconds at a time. Ticks
> > > should be event driven. For embedded systems option B is really
> > > the only way to go to take advantage of the power savings.
> > 
> > I don't know how sensitive embedded platforms are to load imbalance.
> > If they are not sensitive, then we could let the max time idle
> > cpus are allowed to sleep to be few seconds. That way, idle CPU
> > wakes up once in 3 or 4 seconds to check for imbalance and still
> > be able to save power for those 3/4 seconds that it sleeps.
> 
> Not very.  Embedded systems are usually UP so don't care at all.  If an
> embedded system is SMP often it's because one CPU is dedicated to RT
> tasks, and this model will become less common as RT preemption allows
> you to do everything on a single processor.

Yes UP mostly & sounds like this only affects MP systems.

Although there is ARM MP support patches available.
I guess embedded MP systems may be used for multimedia
stuff eventually.

Tony
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