linux-kernel - Re: [patch v4 09/18] sched: add sched

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Date:	Wed, 13 Feb 2013 23:41:07 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	torvalds@...ux-foundation.org, mingo@...hat.com,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	arjan@...ux.intel.com, bp@...en8.de, pjt@...gle.com,
	namhyung@...nel.org, efault@....de, vincent.guittot@...aro.org,
	gregkh@...uxfoundation.org, preeti@...ux.vnet.ibm.com,
	viresh.kumar@...aro.org, linux-kernel@...r.kernel.org
Subject: Re: [patch v4 09/18] sched: add sched_policies in kernel

On 02/12/2013 06:36 PM, Peter Zijlstra wrote:
> On Thu, 2013-01-24 at 11:06 +0800, Alex Shi wrote:
>> Current scheduler behavior is just consider the for larger performance
>> of system. So it try to spread tasks on more cpu sockets and cpu cores
>>
>> To adding the consideration of power awareness, the patchset adds
>> 2 kinds of scheduler policy: powersaving and balance. They will use
>> runnable load util in scheduler balancing. The current scheduling is taken
>> as performance policy.
>>
>> performance: the current scheduling behaviour, try to spread tasks
>>                 on more CPU sockets or cores. performance oriented.
>> powersaving: will pack tasks into few sched group until all LCPU in the
>>                 group is full, power oriented.
>> balance    : will pack tasks into few sched group until group_capacity
>>                 numbers CPU is full, balance between performance and
>> 		powersaving.
> 
> _WHY_ do you start out with so much choice?
> 
> If your power policy is so abysmally poor on performance that you
> already know you need a 3rd policy to keep people happy, maybe you're
> doing something wrong?

Nope, no much performance yield for both of powersaving and balance policy.
Much of testing results in replaying Ingo's email on '0/18' thread --
the cover letter email threads.
https://lkml.org/lkml/2013/2/3/353
https://lkml.org/lkml/2013/2/4/735

I introduce a 'balance' policy just because HT thread LCPU in Intel CPU
is less then 1 usual cpu power. It is used when someone want to save
power but still want tasks have a whole cpu core...
> 
>> +#define SCHED_POLICY_PERFORMANCE	(0x1)
>> +#define SCHED_POLICY_POWERSAVING	(0x2)
>> +#define SCHED_POLICY_BALANCE		(0x4)
>> +
>> +extern int __read_mostly sched_policy;
> 
> I'd much prefer: sched_balance_policy. Scheduler policy is a concept
> already well defined by posix and we don't need it to mean two
> completely different things.
> 

Got it.
-- 
Thanks
    Alex
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