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
domains?