[PATCH v7 5/7] sched: get CPU's usage statistic
From: peterz@infradead.org (Peter Zijlstra)
Date: 2014-10-09 11:36:28
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On Tue, Oct 07, 2014 at 02:13:35PM +0200, Vincent Guittot wrote:
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. The utilization_avg_contrib only takes into account the running time but not the uArch so the utilization_load_avg is in the range [0..SCHED_LOAD_SCALE] to reflect the running load on the CPU. We have to scale the utilization with the capacity of the CPU to get the usage of the latter. The usage can then be compared with the available capacity.
You say cpu_capacity, but in actual fact you use capacity_orig and fail to justify/clarify this.
The frequency scaling invariance is not taken into account in this patchset, it will be solved in another patchset
Maybe explain what the specific invariance issue is that is skipped over for now.
quoted hunk ↗ jump to hunk
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 d3e9067..7364ed4 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c@@ -4551,6 +4551,17 @@ 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;
Like Morten I'm confused by that +1 thing.
+ + return (usage * capacity) >> SCHED_LOAD_SHIFT; +}
A comment with that function that it returns capacity units might clarify shift confusion Morten raised the other day.