linux-kernel - Re: [RFC PATCH] sched: wakeup buddy

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Date:	Thu, 28 Feb 2013 15:42:20 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Mike Galbraith <efault@....de>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Turner <pjt@...gle.com>, Alex Shi <alex.shi@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ram Pai <linuxram@...ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [RFC PATCH] sched: wakeup buddy

On 02/28/2013 03:40 PM, Michael Wang wrote:
> Hi, Mike
> 
> Thanks for your reply.
> 
> On 02/28/2013 03:18 PM, Mike Galbraith wrote:
>> On Thu, 2013-02-28 at 14:38 +0800, Michael Wang wrote:
>>
>>> +				/*
>>> +				 * current is the only task on rq and it is
>>> +				 * going to sleep, current cpu will be a nice
>>> +				 * candidate for p to run on.
>>> +				 */
>>
>> The sync hint only means it might be going to sleep soon, and even then,
>> there can still be enough execution overlap to be a win to schedule
>> cross core.  Sched pipe numbers will always be much prettier if you do
>> wakeup cpu affine, as it's ~100% scheduler and ~100% sync.
> 
> Hmm.. so it's the comparison between 'cache benefit - execution overlap'
> and 'latency - execution overlap'?
> 
> I could not estimate how many latency will be added to wait for current
> going to sleep (it should be faster than access cold data, isn't it?),
> but I really like the cache benefit, unless sync doesn't means current
> is going to sleep every time, but that's the promise of WF_SYNC, isn't it?
> 
> You may lose
>> a lot on other stuff if you interpret the hint as gospel truth.
> 
> Could you please give more details on this point?
> 
>>
>> IMHO, sched pipe is a "how fat have I become" benchmark, not "how well
>> do I perform".  The scheduler performs well when it makes more work
>> happen.  Playing ping-pong with yourself is _exercise_, not a job :)
> 
> That's right, may be I'm using the wrong description, it's the ops/sec
> which has been doubled, that means 'fat', correct?

I mean could we say that more ops/sec means more works has been done?

Regards,
Michael Wang

> 
> Regards,
> Michael Wang
> 
>>
>> -Mike
>>
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