linux-kernel - Re: [RFC PATCH v3 3/5] sched: nominate preferred wakeup cpu

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Date:	Tue, 11 Nov 2008 22:47:51 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Gregory Haskins <gregory.haskins@...il.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	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>
Subject: Re: [RFC PATCH v3 3/5] sched: nominate preferred wakeup cpu

* Gregory Haskins <gregory.haskins@...il.com> [2008-11-11 09:07:58]:

> Peter Zijlstra wrote:
> > 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?
> >   
> 
> From the description, this is exactly what the root-domains were created
> to solve.
> 
> Vaidyanathan,  just declare your object in "struct root_domain" and
> initialize it in init_rootdomain() in kernel/sched.c, and then access it
> via rq->rd to take advantage of this infrastructure.  It will
> automatically follow any partitioning that happens to be configured.

Yep, I agree.  I will use root_domain for this purpose in the next
revision.

Thanks,
Vaidy
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