Date: Tue, 11 Nov 2008 22:18:25 +0530
From: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>,
       Suresh B Siddha <suresh.b.siddha@intel.com>,
       Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>,
       Ingo Molnar <mingo@elte.hu>, 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>
Subject: Re: [RFC PATCH v3 3/5] sched: nominate preferred wakeup cpu
Message-ID: <20081111164825.GS4646@dirshya.in.ibm.com>
Reply-To: svaidy@linux.vnet.ibm.com
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	Linux Kernel <linux-kernel@vger.kernel.org>,
	Suresh B Siddha <suresh.b.siddha@intel.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>,
	Ingo Molnar <mingo@elte.hu>, 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>
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* Peter Zijlstra <a.p.zijlstra@chello.nl> [2008-11-11 14:43:39]:

> On Tue, 2008-11-11 at 00:03 +0530, Vaidyanathan Srinivasan wrote:
> > When the system utilisation is low and more cpus are idle,
> > then the process waking up from sleep should prefer to
> > wakeup an idle cpu from semi-idle cpu package (multi core
> > package) rather than a completely idle cpu package which
> > would waste power.
> > 
> > Use the sched_mc balance logic in find_busiest_group() to
> > nominate a preferred wakeup cpu.
> > 
> > This info can be sored in appropriate sched_domain, but
> > updating this info in all copies of sched_domain is not
> > practical.  For now lets try with a per-cpu variable
> > pointing to a common storage in partition sched domain
> > attribute.  Global variable may not work in partitioned
> > sched domain case.
> 
> Would it make sense to place the preferred_wakeup_cpu stuff in the
> root_domain structure we already have?

Yep, that will be a good idea.  We can get to root_domain from each
CPU's rq and we can get rid of the per-cpu pointers for
preferred_wakeup_cpu as well. I will change the implementation and
re-post.

Thanks,
Vaidy

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