Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq_fair()

[Michael Wang <wangyun@linux.vnet.ibm.com>]

On 02/20/2013 10:05 PM, Mike Galbraith wrote:
> On Wed, 2013-02-20 at 14:32 +0100, Peter Zijlstra wrote: 
>> On Wed, 2013-02-20 at 11:49 +0100, Ingo Molnar wrote:
>>
>>> The changes look clean and reasoable, 
>>
>> I don't necessarily agree, note that O(n^2) storage requirement that
>> Michael failed to highlight ;-)
> 
> (yeah, I mentioned that needs to shrink.. a lot)

Exactly, and I'm going to apply the suggestion now :)

> 
>>> any ideas exactly *why* it speeds up?
>>
>> That is indeed the most interesting part.. There's two parts to
>> select_task_rq_fair(), the 'regular' affine wakeup path, and the
>> fork/exec find_idlest_goo() path. At the very least we need to quantify
>> which of these two parts contributes most to the speedup.
>>
>> In the power balancing discussion we already noted that the
>> find_idlest_goo() is in need of attention.
> 
> Yup, even little stuff like break off the search when load is zero..

Agree, searching in a bunch of idle cpus and their subsets doesn't make
sense...

Regards,
Michael Wang

> unless someone is planning on implementing anti-idle 'course ;-)
> 
> -Mike
> 
> 
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