On 21/09/16 13:34, Vincent Guittot wrote:
Hi Dietmar,
On 21 September 2016 at 12:14, Dietmar Eggemann dietmar.eggemann@arm.com wrote:
Hi Vincent,
On 12/09/16 08:47, Vincent Guittot wrote:
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I guess in the meantime we lost the functionality to remove a cfs_rq from the leaf_cfs_rq list once there are no se's enqueued on it anymore. If e.g. t migrates away from Cpu1, all the cfs_rq's of the task hierarchy (for tg_css_id=2,4,6) owned by Cpu1 stay in the leaf_cfs_rq list.
Shouldn't we reintegrate it? Following patch goes on top of this patch:
I see one problem: Once a cfs_rq has been removed , it will not be periodically updated anymore until the next enqueue. A sleeping task is only attached but not enqueued when it moves into a cfs_rq so its load is added to cfs_rq's load which have to be periodically updated/decayed. So adding a cfs_rq to the list only during an enqueue is not enough in this case.
There was more in the original patch (commit 82958366cfea), the removal of the cfs_rq from the list was only done in case the se->avg.runnable_avg_sum had decayed to 0. Couldn't we use something similar with se->avg.load_avg instead to make sure that these blocked contributions have been decayed before we do the removal?
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 4ac1718560e2..3595b0623b37 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6566,6 +6566,8 @@ static void update_blocked_averages(int cpu) * list_add_leaf_cfs_rq() for details. */ for_each_leaf_cfs_rq(rq, cfs_rq) { + struct sched_entity *se = cfs_rq->tg->se[cpu]; + /* throttled entities do not contribute to load */ if (throttled_hierarchy(cfs_rq)) continue; @@ -6574,8 +6576,12 @@ static void update_blocked_averages(int cpu) update_tg_load_avg(cfs_rq, 0);
/* Propagate pending load changes to the parent */ - if (cfs_rq->tg->se[cpu]) - update_load_avg(cfs_rq->tg->se[cpu], 0, 0); + if (se) { + update_load_avg(se, 0, 0); + + if (!se->avg.load_avg && !cfs_rq->nr_running) + list_del_leaf_cfs_rq(cfs_rq); + } } raw_spin_unlock_irqrestore(&rq->lock, flags); }
Then, only the highest child level of task group will be removed because cfs_rq->nr_running will be > 0 as soon as a child task group is created and enqueued into a task group. Or you should use cfs.h_nr_running instead i don't know all implications
In my tests all cfs_rq's (tg_id=6,4,2) on the source CPU (CPU1) get removed? Do I miss something?
migration/1-16 [001] 67.235292: sched_migrate_task: comm=task0 pid=2210 prio=120 orig_cpu=1 dest_cpu=2 migration/1-16 [001] 67.235295: bprint: enqueue_task_fair: list_add_leaf_cfs_rq: cpu=2 cfs_rq=0xffff80097550d700 tg_id=6 on_list=0 migration/1-16 [001] 67.235298: bprint: enqueue_task_fair: list_add_leaf_cfs_rq: cpu=2 cfs_rq=0xffff800975903700 tg_id=4 on_list=0 migration/1-16 [001] 67.235300: bprint: enqueue_task_fair: list_add_leaf_cfs_rq: cpu=2 cfs_rq=0xffff800974e0fe00 tg_id=2 on_list=0 migration/1-16 [001] 67.235302: bprint: enqueue_task_fair: list_add_leaf_cfs_rq: cpu=2 cfs_rq=0xffff80097fecb6e0 tg_id=1 on_list=1 migration/1-16 [001] 67.235309: bprint: update_blocked_averages: update_blocked_averages: cpu=1 cfs_rq=0xffff80097550d800 tg_id=6 on_list=1 -> migration/1-16 [001] 67.235312: bprint: update_blocked_averages: list_del_leaf_cfs_rq: cpu=1 cfs_rq=0xffff80097550d800 tg_id=6 on_list=1 migration/1-16 [001] 67.235314: bprint: update_blocked_averages: update_blocked_averages: cpu=1 cfs_rq=0xffff800975903600 tg_id=4 on_list=1 -> migration/1-16 [001] 67.235315: bprint: update_blocked_averages: list_del_leaf_cfs_rq: cpu=1 cfs_rq=0xffff800975903600 tg_id=4 on_list=1 migration/1-16 [001] 67.235316: bprint: update_blocked_averages: update_blocked_averages: cpu=1 cfs_rq=0xffff800974e0f600 tg_id=2 on_list=1 -> migration/1-16 [001] 67.235318: bprint: update_blocked_averages: list_del_leaf_cfs_rq: cpu=1 cfs_rq=0xffff800974e0f600 tg_id=2 on_list=1 migration/1-16 [001] 67.235319: bprint: update_blocked_averages: update_blocked_averages: cpu=1 cfs_rq=0xffff80097feb56e0 tg_id=1 on_list=1
If we don't remove these cfs_rq's, IMHO they stay in the list as long as the tg exists.
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