linux-kernel - Re: [PATCH V2 Resend 0/4] Create sched_select_cpu() and use it for workqueues and timers

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Message-ID: <20121126190354.GJ2474@linux.vnet.ibm.com>
Date:	Mon, 26 Nov 2012 11:03:54 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>, pjt@...gle.com,
	paul.mckenney@...aro.org, tglx@...utronix.de, tj@...nel.org,
	suresh.b.siddha@...el.com, venki@...gle.com, mingo@...hat.com,
	peterz@...radead.org, Arvind.Chauhan@....com,
	linaro-dev@...ts.linaro.org, patches@...aro.org,
	pdsw-power-team@....com, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org
Subject: Re: [PATCH V2 Resend 0/4] Create sched_select_cpu() and use it for
 workqueues and timers

On Mon, Nov 26, 2012 at 12:35:52PM -0500, Steven Rostedt wrote:
> On Mon, 2012-11-26 at 09:03 -0800, Paul E. McKenney wrote:
> 
> 
> > If I understand correctly (though also suffering turkey OD), the idea is
> > to offload work to more energy-efficient CPUs.
> 
> This is determined by a CPU that isn't running the idle task? Is it
> because a CPU that just woke up may be running at a lower freq, and thus
> not as efficient? But pushing off to another CPU may cause cache misses
> as well. Wouldn't that also be a factor in efficiencies, if a CPU is
> stalled waiting for memory to be loaded?

Two different microarchitectures -- same instruction set (at user level,
anyway), but different power/performance characteristics.  One set is
optimized for performance, the other for energy efficiency.  For example,
ARM's big.LITTLE architecture.

> I should also ask the obvious. Has these patches shown real world
> efficiencies or is this just a theory? Do these patches actually improve
> battery life when applied?

I must defer to Viresh on this one.

							Thanx, Paul

> Just asking.
> 
> -- Steve
> 
> 

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