Re: [RFC] sched: Limit idle_balance() when it is being used toofrequently

[Peter Zijlstra]

On Wed, Jul 17, 2013 at 09:02:24PM -0700, Jason Low wrote:

> I ran a few AIM7 workloads for the 8 socket HT enabled case and I needed
> to set N to more than 20 in order to get the big performance gains.
> 
> One thing that I thought of was to have N be based on how often idle
> balance attempts does not pull task(s).
> 
> For example, N can be calculated based on the number of idle balance
> attempts for the CPU  since the last "successful" idle balance attempt.
> So if the previous 30 idle balance attempts resulted in no tasks moved,
> then n = 30 / 5. So idle balance gets less time to run as the number of
> unneeded idle balance attempts increases, and thus N will not be set too
> high during situations where idle balancing is "successful" more often.
> Any comments on this idea?

It would be good to get a solid explanation for why we need such high N.
But yes that might work.


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