Re: [PATCH v3 07/12] sched: test the cpu's capacity in wake affine

From: Peter Zijlstra
Date: Thu Jul 10 2014 - 07:07:10 EST

On Mon, Jun 30, 2014 at 06:05:38PM +0200, Vincent Guittot wrote:
> Currently the task always wakes affine on this_cpu if the latter is idle.
> Before waking up the task on this_cpu, we check that this_cpu capacity is not
> significantly reduced because of RT tasks or irq activity.
> Use case where the number of irq and/or the time spent under irq is important
> will take benefit of this because the task that is woken up by irq or softirq
> will not use the same CPU than irq (and softirq) but a idle one which share
> its cache.

The above, doesn't seem to explain:

> + } else if (!(sd->flags & SD_SHARE_PKG_RESOURCES)) {
> + this_eff_load = 0;
> + }
> +
> + balanced = this_eff_load <= prev_eff_load;

this. Why would you unconditionally allow wake_affine across cache
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