On 25 September 2014 21:05, Dietmar Eggemann dietmar.eggemann@arm.com wrote:
On 23/09/14 17:08, 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.
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.
In case the weight of a sched group is greater than 1, you might loose the information that the whole sched group is over-utilized too.
that's exactly for sched_group with more than 1 CPU that we need to cap the usage of a CPU to 100%. Otherwise, the group could be seen as overloaded (CPU0 usage at 121% + CPU1 usage at 80%) whereas CPU1 has 20% of available capacity
You add up the individual cpu usage values for a group by sgs->group_usage += get_cpu_usage(i) in update_sg_lb_stats and later use sgs->group_usage in group_is_overloaded to compare it against sgs->group_capacity (taking imbalance_pct into consideration).
return (usage * capacity) >> SCHED_LOAD_SHIFT;Nit-pick: Since you're multiplying by a capacity value (rq->cpu_capacity_orig) you should shift by SCHED_CAPACITY_SHIFT.
we want to compare the output of the function with some capacity figures so i think that >> SCHED_LOAD_SHIFT is the right operation.
Just to make sure: You do this scaling of usage by cpu_capacity_orig here only to cater for the fact that cpu_capacity_orig might be uarch scaled (by arch_scale_cpu_capacity, !SMT) in update_cpu_capacity while
I do this for any system with CPUs that have an original capacity that is different from SCHED_CAPACITY_SCALE so it's for both uArch and SMT.
utilization_load_avg is currently not. We don't even uArch scale on ARM TC2 big.LITTLE platform in mainline today due to the missing clock-frequency property in the device tree.
sorry i don't catch your point
I think it's hard for people to grasp that your patch-set takes uArch scaling of capacity into consideration but not frequency scaling of capacity (via arch_scale_freq_capacity, not used at the moment).
+}
/*
- select_task_rq_fair: Select target runqueue for the waking task in domains
- that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE,
@@ -5663,6 +5674,7 @@ struct sg_lb_stats { unsigned long sum_weighted_load; /* Weighted load of group's tasks */ unsigned long load_per_task; unsigned long group_capacity;
unsigned long group_usage; /* Total usage of the group */ unsigned int sum_nr_running; /* Nr tasks running in the group */ unsigned int group_capacity_factor; unsigned int idle_cpus;@@ -6037,6 +6049,7 @@ static inline void update_sg_lb_stats(struct lb_env *env, load = source_load(i, load_idx);
sgs->group_load += load;
sgs->group_usage += get_cpu_usage(i); sgs->sum_nr_running += rq->cfs.h_nr_running; if (rq->nr_running > 1)