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SubjectRe: [PATCH v3] sched/pelt: fix update_blocked_averages() for dl and rt
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On 08/31/2018 08:22 AM, Vincent Guittot wrote:
> update_blocked_averages() is called to periodiccally decay the stalled load
> of idle CPUs and to sync all loads before running load balance.
>
> When cfs rq is idle, it trigs a load balance during pick_next_task_fair()
> in order to potentially pull tasks and to use this newly idle CPU. This
> load balance happens whereas prev task from another class has not been put
> and its utilization updated yet. This may lead to wrongly account running
> time as idle time for rt or dl classes.
>
> Test that no rt or dl task is running when updating their utilization in
> update_blocked_averages().

Shouldn't this be 's/that no/if an' ?

You still update the utilization of the rt or dl task if they are
running (accrue + decay) instead of only decay. Similar to the
'cfs_rq->curr != NULL' in __update_load_avg_cfs_rq().

> We still update rt and dl utilization instead of simply skipping them to
> make sure that all metrics are synced when used during load balance.

I assume this sentence is indirectly saying this.

>
> Fixes: 371bf4273269 ("sched/rt: Add rt_rq utilization tracking")
> Fixes: 3727e0e16340 ("sched/dl: Add dl_rq utilization tracking")
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
>
> -V3
> - move rq->curr dereference under the rq->lock
>
> -V2
> - Add missing fixes tags
> - apply fix to other version of update_blocked_averages
>
> kernel/sched/fair.c | 14 ++++++++++----
> 1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 309c93f..53bbcd4 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7262,6 +7262,7 @@ static void update_blocked_averages(int cpu)
> {
> struct rq *rq = cpu_rq(cpu);
> struct cfs_rq *cfs_rq, *pos;
> + const struct sched_class *curr_class;
> struct rq_flags rf;
> bool done = true;
>
> @@ -7298,8 +7299,10 @@ static void update_blocked_averages(int cpu)
> if (cfs_rq_has_blocked(cfs_rq))
> done = false;
> }
> - update_rt_rq_load_avg(rq_clock_task(rq), rq, 0);
> - update_dl_rq_load_avg(rq_clock_task(rq), rq, 0);
> +
> + curr_class = rq->curr->sched_class;
> + update_rt_rq_load_avg(rq_clock_task(rq), rq, curr_class == &rt_sched_class);
> + update_dl_rq_load_avg(rq_clock_task(rq), rq, curr_class == &dl_sched_class);
> update_irq_load_avg(rq, 0);
> /* Don't need periodic decay once load/util_avg are null */
> if (others_have_blocked(rq))
> @@ -7364,13 +7367,16 @@ static inline void update_blocked_averages(int cpu)
> {
> struct rq *rq = cpu_rq(cpu);
> struct cfs_rq *cfs_rq = &rq->cfs;
> + const struct sched_class *curr_class;
> struct rq_flags rf;
>
> rq_lock_irqsave(rq, &rf);
> update_rq_clock(rq);
> update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq);
> - update_rt_rq_load_avg(rq_clock_task(rq), rq, 0);
> - update_dl_rq_load_avg(rq_clock_task(rq), rq, 0);
> +
> + curr_class = rq->curr->sched_class;
> + update_rt_rq_load_avg(rq_clock_task(rq), rq, curr_class == &rt_sched_class);
> + update_dl_rq_load_avg(rq_clock_task(rq), rq, curr_class == &dl_sched_class);
> update_irq_load_avg(rq, 0);
> #ifdef CONFIG_NO_HZ_COMMON
> rq->last_blocked_load_update_tick = jiffies;
>

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