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

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Date:	Tue, 11 Nov 2008 09:07:58 -0500
From:	Gregory Haskins <gregory.haskins@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	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

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.

-Greg



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