linux-kernel - Re: [PATCH] sched: smart wake-affine

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Message-ID: <51D5428D.7080805@linux.vnet.ibm.com>
Date:	Thu, 04 Jul 2013 17:38:21 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
	Alex Shi <alex.shi@...el.com>,
	Namhyung Kim <namhyung@...nel.org>,
	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: [PATCH] sched: smart wake-affine

On 07/04/2013 05:13 PM, Peter Zijlstra wrote:
[snip]
> 
> Right, but something like the below is limited in cost to at most 32/64 (I
> forgot the type) shifts. Now its probably not worth doing, but it shows
> things like that can be done in 'constant' time.
> 
>   now = jiffies;
>   if (now - p->last_switch_decay > 8*sizeof(p->nr_wakee_switch)*HZ) {
> 	p->nr_wakee_switch = 0;
> 	p->last_switch_decay = now;
>   } else while (now > p->last_switch_decay + HZ) {
> 	p->nr_wakee_switch >>= 1;
> 	p->last_switch_decay += HZ;
>   }

Hmm...interesting, some kind of cataclysm decay, not sure how it works
but yes, the cost was capped.

Well, seems like we still have many follow-up research works after fix
the issue ;-)

Regards,
Michael Wang

> 
> 
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