On Wed, Mar 27, 2013 at 03:51:51PM +0530, Preeti U Murthy wrote:
Hi,
On 03/26/2013 05:56 PM, Peter Zijlstra wrote:
On Fri, 2013-03-22 at 13:25 +0100, Vincent Guittot wrote:
+static bool is_buddy_busy(int cpu) +{
struct rq *rq = cpu_rq(cpu);/** A busy buddy is a CPU with a high load or a small load witha lot of
* running tasks.*/return (rq->avg.runnable_avg_sum >(rq->avg.runnable_avg_period / (rq->nr_running- 2)));
+}
Why does the comment talk about load but we don't see it in the equation. Also, why does nr_running matter at all? I thought we'd simply bother with utilization, if fully utilized we're done etc..
Peter, lets say the run-queue has 50% utilization and is running 2 tasks. And we wish to find out if it is busy. We would compare this metric with the cpu power, which lets say is 100.
rq->util * 100 < cpu_of(rq)->power.
In the above scenario would we declare the cpu _not_busy? Or would we do the following:
(rq->util * 100) * #nr_running < cpu_of(rq)->power and conclude that it is just enough _busy_ to not take on more processes?
That is just confused... ->power doesn't have anything to do with a per-cpu measure. ->power is a inter-cpu measure of relative compute capacity.
Mixing in nr_running confuses things even more; it doesn't matter how many tasks it takes to push utilization up to 100%; once its there the cpu simply cannot run more.
So colour me properly confused..