Re: [PATCH] sched: smart wake-affine

[Michael Wang <wangyun@linux.vnet.ibm.com>]

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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