linux-kernel - Re: [DISCUSSION] removing variety rq->cpu

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Message-ID: <51AD549A.9010903@intel.com>
Date:	Tue, 04 Jun 2013 10:44:42 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Michael Wang <wangyun@...ux.vnet.ibm.com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Turner <pjt@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Namhyung Kim <namhyung@...nel.org>,
	Mike Galbraith <efault@....de>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>
Subject: Re: [DISCUSSION] removing variety rq->cpu_load ?

On 06/04/2013 10:33 AM, Michael Wang wrote:
> Hi, Alex
> 
> On 06/04/2013 09:51 AM, Alex Shi wrote:
>> resend with a new subject.
> 
> Forgive me but I'm a little lost on this thread...
> 
> So we are planing to rely on instant 'cpu_load[0]' and decayed
> 'runnable_load_avg' only, do we?

cpu_load is a kind of time decay for cpu load, but after runnable load introduced, 
the decay functionality is a kind duplicate with it.
So, remove them will make code simple. The idea were mentioned by Paul, Peter and I.

the following is Peter's word of this affair.

> Agreed, esp. the plethora of weird idx things we currently have. If we need to
> re-introduce something it would likely only be the busy case and for that we
> can immediately link to the balance interval or so.


>
> 
> Regards,
> Michael Wang
> 
>>
>>> Peter,
>>>
>>> I just tried to remove the variety rq.cpu_load, by the following patch. 
>>> Because forkexec_idx and busy_idx are all zero, after the patch system just keep cpu_load[0]
>>> and remove other values.
>>> I tried the patch base 3.10-rc3 and latest tip/sched/core with benchmark dbench,tbench,
>>> aim7,hackbench. and oltp of sysbench. Seems performance doesn't change clear.
>>> So, for my tested machines, core2, NHM, SNB, with 2 or 4 CPU sockets, and above tested
>>> benchmark. We are fine to remove the variety cpu_load. 
>>> Don't know if there some other concerns on other scenarios.
>>>
>>> ---
>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>> index 590d535..f0ca983 100644
>>> --- a/kernel/sched/fair.c
>>> +++ b/kernel/sched/fair.c
>>> @@ -4626,7 +4626,7 @@ static inline void update_sd_lb_stats(struct lb_env *env,
>>>         if (child && child->flags & SD_PREFER_SIBLING)
>>>                 prefer_sibling = 1;
>>>  
>>> -       load_idx = get_sd_load_idx(env->sd, env->idle);
>>> +       load_idx = 0; //get_sd_load_idx(env->sd, env->idle);
>>>  
>>>         do {
>>>                 int local_group;
>>>
>>>
>>
>>
> 


-- 
Thanks
    Alex
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