linux-kernel - Re: [PATCH V5 0/5] Queue work on power efficient wq

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Date:	Mon, 8 Jul 2013 17:37:16 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	tj@...nel.org, davem@...emloft.net, airlied@...hat.com,
	axboe@...nel.dk, tglx@...utronix.de, peterz@...radead.org,
	mingo@...hat.com, rostedt@...dmis.org,
	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	robin.randhawa@....com, Steve.Bannister@....com, Livi@...per.es
Subject: Re: [PATCH V5 0/5] Queue work on power efficient wq

Hello,

On Wed, Apr 24, 2013 at 05:12:52PM +0530, Viresh Kumar wrote:
> This patchset was called: "Create sched_select_cpu() and use it for workqueues"
> for the first three versions.
> 
> Earlier discussions over v3, v2 and v1 can be found here:
> https://lkml.org/lkml/2013/3/18/364
> http://lists.linaro.org/pipermail/linaro-dev/2012-November/014344.html
> http://www.mail-archive.com/linaro-dev@lists.linaro.org/msg13342.html
> 
> V4 is here:
> https://lkml.org/lkml/2013/3/31/55
> 
> Workqueues can be performance or power oriented. For performance we may want to
> keep them running on a single cpu, so that it remains cache hot. For power we
> can give scheduler the liberty to choose target cpu for running work handler.
> 
> Later one (Power oriented WQ) can be achieved if the workqueue is allocated with
> WQ_UNBOUND flag. Enabling CONFIG_WQ_POWER_EFFICIENT will set
> 'wq_power_efficient' to 'true'. Setting 'power_efficient' boot param will
> override value of 'wq_power_efficient' variable. When 'wq_power_efficient' is
> set to 'true', we will convert WQ_POWER_EFFICIENT flag to WQ_UNBOUND on wq
> allocation. And so scheduler will have the liberty to choose where to run this
> work.
> 
> Here we are migrating few users of workqueues to WQ_POWER_EFFICIENT. These
> drivers are found to be very much active on idle or lightly busy system and
> using WQ_POWER_EFFICIENT for these gave impressive results.
> 
> These would be used in power saving mode only if relevant configs are enabled
> at compile time or in bootargs. Otherwise behavior is unchanged.
> 
> Setup:
> -----
> - ARM Vexpress TC2 - big.LITTLE CPU
> - Core 0-1: A15, 2-4: A7
> - rootfs: linaro-ubuntu-devel
This patch set hit my tree now. I wonder if it makes sense to make
WQ_POWER_EFFICIENT_DEFAULT depend on SMP. (Oh wait, big.LITTLE isn't
SMP, so probably there is a better symbol to depend on?)

Just my 2 cent
Uwe


-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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