linux-kernel - Re: [RFC PATCH] sched: wake-affine throttle

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Date:	Tue, 26 Mar 2013 10:45:18 +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>,
	Namhyung Kim <namhyung@...nel.org>,
	Alex Shi <alex.shi@...el.com>, Paul Turner <pjt@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	Ram Pai <linuxram@...ibm.com>
Subject: Re: [RFC PATCH] sched: wake-affine throttle

On 03/25/2013 10:31 PM, Mike Galbraith wrote:
[snip]
>>
>> Do you mean 1ms interval is still too big? and you prefer to have a 0
>> option?
> 
> Not really, I just think a fixed interval may not be good enough without
> some idle time consideration.  Once a single load gets going less
> balancing is more, it's just when load is fluctuating a lot, and mixed
> loads where I can imagine troubles.
> 
> Perhaps ramp up to knob interval after an idle period trigger of.. say
> migration_cost, or whatever.  Something dirt simple that makes it open
> the gates when it's most likely to matter.
> 

So a dynamically adjustment, sounds attractively ;-)

However, IMHO, I don't think we could be able to figure out when to
adjust and how to adjust, actually we even don't have the data to count
on, otherwise, there is no necessary to throttle the wake-affine stuff
at all...

May be do such work in user space will be better?

This knob is nothing but compromise, besides, it's a highlight to notify
us we still have a feature waiting for improve, if later we have the way
to build an accurate wake-affine, remove the knob should be easy.

Regards,
Michael Wang

> 
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