linux-kernel - Re: [PATCH V2 0/3] Create sched_select

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Date:	Mon, 15 Oct 2012 10:08:38 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	mingo@...hat.com, peterz@...radead.org, tglx@...utronix.de
Cc:	pjt@...gle.com, paul.mckenney@...aro.org, tj@...nel.org,
	suresh.b.siddha@...el.com, venki@...gle.com,
	robin.randhawa@....com, Steve.Bannister@....com,
	amit.kucheria@...aro.org, vincent.guittot@...aro.org,
	linaro-dev@...ts.linaro.org, patches@...aro.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 0/3] Create sched_select_cpu() and use it in workqueues

On 27 September 2012 14:34, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> This is V2 of my sched_select_cpu() work.
>
> In order to save power, it would be useful to schedule work onto non-IDLE cpus
> instead of waking up an IDLE one.
>
> To achieve this, we need scheduler to guide kernel frameworks (like: timers &
> workqueues) on which is the most preferred CPU that must be used for these
> tasks.
>
> This patchset is about implementing this concept.
>
> - The first patch adds sched_select_cpu() routine which returns the preferred
>   cpu which is non-idle.
> - Second patch removes idle_cpu() calls from timer & hrtimer.
> - Third patch is about adapting this change in workqueue framework.
>
> Earlier discussions over v1 can be found here:
> http://www.mail-archive.com/linaro-dev@lists.linaro.org/msg13342.html
>
> Earlier discussions over this concept were done at last LPC:
> http://summit.linuxplumbersconf.org/lpc-2012/meeting/90/lpc2012-sched-timer-workqueue/
>
> Module created for testing this behavior is present here:
> http://git.linaro.org/gitweb?p=people/vireshk/module.git;a=summary
>
> Following are the steps followed in test module:
> 1. Run single work on each cpu
> 2. This work will start a timer after x (tested with 10) jiffies of delay
> 3. Timer routine queues a work... (This may be called from idle or non-idle cpu)
>    and starts the same timer again STEP 3 is done for n number of times (i.e.
>    queuing n works, one after other)
> 4. All works will call a single routine, which will count following per cpu:
>  - Total works processed by a CPU
>  - Total works processed by a CPU, which are queued from it
>  - Total works processed by a CPU, which aren't queued from it
>
> Setup:
> -----
> - ARM Vexpress TC2 - big.LITTLE CPU
> - Core 0-1: A15, 2-4: A7
> - rootfs: linaro-ubuntu-nano
>
> Results:
> -------
> Without Workqueue Modification, i.e. PATCH 3/3:
> [ 2493.022335] Workqueue Analyser: works processsed by CPU0, Total: 1000, Own: 0, migrated: 0
> [ 2493.047789] Workqueue Analyser: works processsed by CPU1, Total: 1000, Own: 0, migrated: 0
> [ 2493.072918] Workqueue Analyser: works processsed by CPU2, Total: 1000, Own: 0, migrated: 0
> [ 2493.098576] Workqueue Analyser: works processsed by CPU3, Total: 1000, Own: 0, migrated: 0
> [ 2493.123702] Workqueue Analyser: works processsed by CPU4, Total: 1000, Own: 0, migrated: 0
>
> With Workqueue Modification, i.e. PATCH 3/3:
> [ 2493.022335] Workqueue Analyser: works processsed by CPU0, Total: 1002, Own: 999, migrated: 3
> [ 2493.047789] Workqueue Analyser: works processsed by CPU1, Total: 998,  Own: 997, migrated: 1
> [ 2493.072918] Workqueue Analyser: works processsed by CPU2, Total: 1013, Own: 996, migrated: 17
> [ 2493.098576] Workqueue Analyser: works processsed by CPU3, Total: 998,  Own: 993, migrated: 5
> [ 2493.123702] Workqueue Analyser: works processsed by CPU4, Total: 989,  Own: 987, migrated: 2
>
> V1->V2
> -----
> - New SD_* macros removed now and earlier ones used
> - sched_select_cpu() rewritten and it includes the check on current cpu's
>   idleness.
> - cpu_idle() calls from timer and hrtimer removed now.
> - Patch 2/3 from V1, removed as it doesn't apply to latest workqueue branch from
>   tejun.
> - CONFIG_MIGRATE_WQ removed and so is wq_select_cpu()
> - sched_select_cpu() called only from __queue_work()
> - got tejun/for-3.7 branch in my tree, before making workqueue changes.
>
> Viresh Kumar (3):
>   sched: Create sched_select_cpu() to give preferred CPU for power
>     saving
>   timer: hrtimer: Don't check idle_cpu() before calling
>     get_nohz_timer_target()
>   workqueue: Schedule work on non-idle cpu instead of current one

Hi Guys,

I totally understand since last few weeks you guys were very busy as the
merge window was around. So, didn't tried to disturb you then :)

Can you please share your viewpoint on this patchset now? And also
the running timer migration patch (which was sent separately)?

Thanks in Advance.

--
viresh
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