linux-kernel - Re: [PATCH RFC/TEST] sched: make sync affine wakeups work

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Date:	Mon, 05 May 2014 10:08:31 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
CC:	Preeti Murthy <preeti.lkml@...il.com>,
	Rik van Riel <riel@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	george.mccollister@...il.com, ktkhai@...allels.com
Subject: Re: [PATCH RFC/TEST] sched: make sync affine wakeups work

On 05/04/2014 05:34 PM, Mike Galbraith wrote:
> On Sun, 2014-05-04 at 17:14 +0530, Preeti Murthy wrote: 
>> Hi Rik, Mike
>>
>> On Fri, May 2, 2014 at 12:00 PM, Rik van Riel <riel@...hat.com> wrote:
>>> On 05/02/2014 02:13 AM, Mike Galbraith wrote:
>>>> On Fri, 2014-05-02 at 00:42 -0400, Rik van Riel wrote:
>>>>
>>>>> Whether or not this is the right thing to do remains to be seen,
>>>>> but it does allow us to verify whether or not the wake_affine
>>>>> strategy of always doing affine wakeups and only disabling them
>>>>> in a specific circumstance is sound, or needs rethinking...
>>>>
>>>> Yes, it needs rethinking.
>>>>
>>>> I know why you want to try this, yes, select_idle_sibling() is very much
>>>> a two faced little bitch.
>>>
>>> My biggest problem with select_idle_sibling and wake_affine in
>>> general is that it will override NUMA placement, even when
>>> processes only wake each other up infrequently...
>>
>> As far as my understanding goes, the logic in select_task_rq_fair()
>> does wake_affine() or calls select_idle_sibling() only at those
>> levels of sched domains where the flag SD_WAKE_AFFINE is set.
>> This flag is not set at the numa domain and hence they will not be
>> balancing across numa nodes. So I don't understand how
>> *these functions* are affecting NUMA placements.
> 
> Depends on how far away node yonder is I suppose.
> 
> static inline int sd_local_flags(int level)
> {
>         if (sched_domains_numa_distance[level] > RECLAIM_DISTANCE)
>                 return 0;
> 
>         return SD_BALANCE_EXEC | SD_BALANCE_FORK | SD_WAKE_AFFINE;
> }
> 
> 

Hmm thanks Mike, I totally missed this!

Regards
Preeti U Murthy

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