Date: Thu, 18 Dec 2008 21:19:38 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>,
        Suresh B Siddha <suresh.b.siddha@intel.com>,
        Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Dipankar Sarma <dipankar@in.ibm.com>,
        Balbir Singh <balbir@linux.vnet.ibm.com>,
        Vatsa <vatsa@linux.vnet.ibm.com>, Gautham R Shenoy <ego@in.ibm.com>,
        Andi Kleen <andi@firstfloor.org>, David Collier-Brown <davecb@sun.com>,
        Tim Connors <tconnors@astro.swin.edu.au>,
        Max Krasnyansky <maxk@qualcomm.com>,
        Gregory Haskins <gregory.haskins@gmail.com>,
        Pavel Machek <pavel@suse.cz>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v7 0/8] Tunable sched_mc_power_savings=n
Message-ID: <20081218201938.GB12376@elte.hu>
References: <20081218175313.29812.4781.stgit@drishya.in.ibm.com>
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* Vaidyanathan Srinivasan <svaidy@linux.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
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