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

[Balbir Singh <balbir@linux.vnet.ibm.com>]

Vaidyanathan Srinivasan wrote:
> * 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.

Did you see Vatsa's comments? root_domain will no work if you have more than one
preferred_wakeup_cpu per domain.

-- 
	Balbir