linux-kernel - Re: [PATCH v3 17/22] sched: packing small tasks in wake/exec balancing

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Date:	Wed, 16 Jan 2013 14:11:53 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Namhyung Kim <namhyung@...nel.org>
CC:	Morten Rasmussen <Morten.Rasmussen@....com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"bp@...en8.de" <bp@...en8.de>, "pjt@...gle.com" <pjt@...gle.com>,
	"efault@....de" <efault@....de>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 17/22] sched: packing small tasks in wake/exec balancing

On 01/14/2013 03:13 PM, Namhyung Kim wrote:
> On Fri, 11 Jan 2013 11:47:03 +0800, Alex Shi wrote:
>> On 01/11/2013 01:17 AM, Morten Rasmussen wrote:
>>> On Sat, Jan 05, 2013 at 08:37:46AM +0000, Alex Shi wrote:
>>>> If the wake/exec task is small enough, utils < 12.5%, it will
>>>> has the chance to be packed into a cpu which is busy but still has space to
>>>> handle it.
>>>>
>>>> Signed-off-by: Alex Shi <alex.shi@...el.com>
>>>> ---
> [snip]
>>> I may be missing something, but could the expression be something like
>>> the below instead?
>>>
>>> Create a putil < 12.5% check before the loop. There is no reason to
>>> recheck it every iteration. Then:
> 
> Agreed.  Also suggest that the checking local cpu can also be moved
> before the loop so that it can be used without going through the loop if
> it's vacant enough.

Yes, thanks for suggestion!
> 
>>>
>>> vacancy = FULL_UTIL - (rq->util + putil)
>>>
>>> should be enough?
>>>
>>>> +
>>>> +		/* bias toward local cpu */
>>>> +		if (vacancy > 0 && (i == this_cpu))
>>>> +			return i;
>>>> +
>>>> +		if (vacancy > 0 && vacancy < min_vacancy) {
>>>> +			min_vacancy = vacancy;
>>>> +			idlest = i;
>>>
>>> "idlest" may be a bit misleading here as you actually select busiest cpu
>>> that have enough spare capacity to take the task.
>>
>> Um, change to leader_cpu?
> 
> vacantest? ;-)

hard to the ward in google. are you sure it is better than leader_cpu?  :)
> 
> Thanks,
> Namhyung
> 


-- 
Thanks Alex
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