linux-kernel - Re: [PATCH v7 0/8] Tunable sched_mc_power

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Message-ID: <20081219082431.GD22463@dirshya.in.ibm.com>
Date:	Fri, 19 Dec 2008 13:54:31 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vatsa <vatsa@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Andi Kleen <andi@...stfloor.org>,
	David Collier-Brown <davecb@....com>,
	Tim Connors <tconnors@...ro.swin.edu.au>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Gregory Haskins <gregory.haskins@...il.com>,
	Pavel Machek <pavel@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v7 0/8] Tunable sched_mc_power_savings=n

* Ingo Molnar <mingo@...e.hu> [2008-12-18 21:19:38]:

> 
> * Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> wrote:
> 
> > Hi,
> > 
> > The existing power saving loadbalancer CONFIG_SCHED_MC attempts to run 
> > the workload in the system on minimum number of CPU packages and tries 
> > to keep rest of the CPU packages idle for longer duration. Thus 
> > consolidating workloads to fewer packages help other packages to be in 
> > idle state and save power.  The current implementation is very 
> > conservative and does not work effectively across different workloads. 
> > Initial idea of tunable sched_mc_power_savings=n was proposed to enable 
> > tuning of the power saving load balancer based on the system 
> > configuration, workload characteristics and end user requirements.
> > 
> > The power savings and performance of the given workload in an under 
> > utilised system can be controlled by setting values of 0, 1 or 2 to 
> > /sys/devices/system/cpu/sched_mc_power_savings with 0 being highest 
> > performance and least power savings and level 2 indicating maximum power 
> > savings even at the cost of slight performance degradation.
> > 
> > Please refer to the following discussions and article for details.
> > 
> > [1]Making power policy just work
> > http://lwn.net/Articles/287924/ 
> > 
> > [2][RFC v1] Tunable sched_mc_power_savings=n
> > http://lwn.net/Articles/287882/
> >                                                                                                                
> > v2: http://lwn.net/Articles/297306/
> > v3: http://lkml.org/lkml/2008/11/10/260
> > v4: http://lkml.org/lkml/2008/11/21/47
> > v5: http://lkml.org/lkml/2008/12/11/178
> > v6: http://lwn.net/Articles/311830/
> > 
> > The following series of patch demonstrates the basic framework for
> > tunable sched_mc_power_savings.
> > 
> > This version of the patch incorporates comments and feedback received
> > on the previous post from Andrew Morton.
> > 
> > Changes form v6:
> > ----------------
> > * Convert BALANCE_FOR_xx_POWER and related macros to inline functions
> >   based on comments from Andrew and Ingo.
> > * Ran basic kernelbench test and did not see any performance variation
> >   due to the changes.
> > 
> > Changes form v5:
> > ---------------
> > * Fixed the sscanf bug and checking for (p->flags & PF_KTHREAD)
> > * Dropped the RFC prefix to indicate that the patch is ready for
> >   testing and inclusion  
> > * Patch series against 2.6.28-rc8 kernel
> 
> thanks, applied - and i started testing them. It needed some help here and 
> there to resolve conflicts with pending cpumask changes. Could you please 
> double-check the merged up end result in the latest scheduler devel tree:
> 
>   http://people.redhat.com/mingo/tip.git/README

Thanks Ingo.  I will review and check the cpumask changes.
I will test the tip tree as well and provide you feedback.

I will look forward to test/bug reports from others on the patch
series and help with the fix.

--Vaidy
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