Hi Peter,
On 04/26/2013 03:48 PM, Peter Zijlstra wrote:
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.
Ok.
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.
True, this is from the perspective of the CPU. But will not the tasks on this CPU get throttled if, you find the utilization of this CPU < 100% and decide to put more tasks on it?
Regards Preeti U Murthy