Re: [RFC] sched: CPU topology try

[Peter Zijlstra]

On Wed, Jan 08, 2014 at 12:52:28PM +0000, Morten Rasmussen wrote:

> If I remember correctly, Alex used the rq runnable_avg_sum (in rq->avg)
> for this. It is the most obvious choice, but it takes ages to reach
> 100%.
> 
> #define LOAD_AVG_MAX_N 345
> 
> Worst case it takes 345 ms from the system is becomes fully utilized
> after a long period of idle until the rq runnable_avg_sum reaches 100%.
> 
> An unweigthed version of cfs_rq->runnable_load_avg and blocked_load_avg
> wouldn't have that delay.

Right.. not sure we want to involve blocked load on the utilization
metric, but who knows maybe that does make sense.

But yes, we need unweighted runnable_avg.

> Also, if we are changing the load balance behavior when all cpus are
> fully utilized

We already have this tipping point. See all the has_capacity bits. But
yes, it'd get more involved I suppose.

> we may need to think about cases where the load is
> hovering around the saturation threshold. But I don't think that is
> important yet.

Yah.. I'm going to wait until we have a fail case that can give us
some guidance before really pondering this though :-)
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