On Fri, Sep 26, 2014 at 01:17:43PM +0100, Vincent Guittot wrote:

On 25 September 2014 21:05, Dietmar Eggemann [off-list ref] wrote:

quoted

On 23/09/14 17:08, Vincent Guittot wrote:

quoted

Monitor the usage level of each group of each sched_domain level. The usage is
the amount of cpu_capacity that is currently used on a CPU or group of CPUs.
We use the utilization_load_avg to evaluate the usage level of each group.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
 kernel/sched/fair.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2cf153d..4097e3f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c

@@ -4523,6 +4523,17 @@ static int select_idle_sibling(struct task_struct *p, int target)
      return target;
 }

+static int get_cpu_usage(int cpu)
+{
+     unsigned long usage = cpu_rq(cpu)->cfs.utilization_load_avg;
+     unsigned long capacity = capacity_orig_of(cpu);
+
+     if (usage >= SCHED_LOAD_SCALE)
+             return capacity + 1;

Why you are returning rq->cpu_capacity_orig + 1 (1025) in case
utilization_load_avg is greater or equal than 1024 and not usage or
(usage * capacity) >> SCHED_LOAD_SHIFT too?

The usage can't be higher than the full capacity of the CPU because
it's about the running time on this CPU. Nevertheless, usage can be
higher than SCHED_LOAD_SCALE because of unfortunate rounding in
avg_period and running_load_avg or just after migrating tasks until
the average stabilizes with the new running time.

I fully agree that the cpu usage should be capped to capacity, but why
do you return capacity + 1? I would just return capacity, no?

Now that you have gotten rid of 'usage' everywhere else, shouldn't this
function be renamed to get_cpu_utilization()?