Messages in this thread Patch in this message | | | Date | Fri, 21 Nov 2014 13:36:12 +0800 | From | Wanpeng Li <> | Subject | Re: [PATCH v6 4/6] sched: get CPU's usage statistic |
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Hi Vincent, On 9/26/14, 8:17 PM, Vincent Guittot wrote: > 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.
Could you explain more why '>> SCHED_LOAD_SHIFT' instead of '>> SCHED_CAPACITY_SHIFT'?
Regards, Wanpeng Li
> >> 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) >>> >> > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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