| From f405c3ed226ee72b59b58b7285472fc17d83ecaf Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Mon, 21 Jun 2021 11:37:51 +0100 |
| Subject: sched/rt: Fix RT utilization tracking during policy change |
| |
| From: Vincent Donnefort <vincent.donnefort@arm.com> |
| |
| [ Upstream commit fecfcbc288e9f4923f40fd23ca78a6acdc7fdf6c ] |
| |
| RT keeps track of the utilization on a per-rq basis with the structure |
| avg_rt. This utilization is updated during task_tick_rt(), |
| put_prev_task_rt() and set_next_task_rt(). However, when the current |
| running task changes its policy, set_next_task_rt() which would usually |
| take care of updating the utilization when the rq starts running RT tasks, |
| will not see a such change, leaving the avg_rt structure outdated. When |
| that very same task will be dequeued later, put_prev_task_rt() will then |
| update the utilization, based on a wrong last_update_time, leading to a |
| huge spike in the RT utilization signal. |
| |
| The signal would eventually recover from this issue after few ms. Even if |
| no RT tasks are run, avg_rt is also updated in __update_blocked_others(). |
| But as the CPU capacity depends partly on the avg_rt, this issue has |
| nonetheless a significant impact on the scheduler. |
| |
| Fix this issue by ensuring a load update when a running task changes |
| its policy to RT. |
| |
| Fixes: 371bf427 ("sched/rt: Add rt_rq utilization tracking") |
| Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com> |
| Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> |
| Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> |
| Link: https://lore.kernel.org/r/1624271872-211872-2-git-send-email-vincent.donnefort@arm.com |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| kernel/sched/rt.c | 17 ++++++++++++----- |
| 1 file changed, 12 insertions(+), 5 deletions(-) |
| |
| diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c |
| index 49ec096a8aa1..b5cf418e2e3f 100644 |
| --- a/kernel/sched/rt.c |
| +++ b/kernel/sched/rt.c |
| @@ -2291,13 +2291,20 @@ void __init init_sched_rt_class(void) |
| static void switched_to_rt(struct rq *rq, struct task_struct *p) |
| { |
| /* |
| - * If we are already running, then there's nothing |
| - * that needs to be done. But if we are not running |
| - * we may need to preempt the current running task. |
| - * If that current running task is also an RT task |
| + * If we are running, update the avg_rt tracking, as the running time |
| + * will now on be accounted into the latter. |
| + */ |
| + if (task_current(rq, p)) { |
| + update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 0); |
| + return; |
| + } |
| + |
| + /* |
| + * If we are not running we may need to preempt the current |
| + * running task. If that current running task is also an RT task |
| * then see if we can move to another run queue. |
| */ |
| - if (task_on_rq_queued(p) && rq->curr != p) { |
| + if (task_on_rq_queued(p)) { |
| #ifdef CONFIG_SMP |
| if (p->nr_cpus_allowed > 1 && rq->rt.overloaded) |
| rt_queue_push_tasks(rq); |
| -- |
| 2.30.2 |
| |