| From 10d626cd70e9e51b7fd154d73fb9cf8633455f23 Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Mon, 21 Jun 2021 11:37:52 +0100 |
| Subject: sched/rt: Fix Deadline utilization tracking during policy change |
| |
| From: Vincent Donnefort <vincent.donnefort@arm.com> |
| |
| [ Upstream commit d7d607096ae6d378b4e92d49946d22739c047d4c ] |
| |
| DL keeps track of the utilization on a per-rq basis with the structure |
| avg_dl. This utilization is updated during task_tick_dl(), |
| put_prev_task_dl() and set_next_task_dl(). However, when the current |
| running task changes its policy, set_next_task_dl() which would usually |
| take care of updating the utilization when the rq starts running DL |
| tasks, will not see a such change, leaving the avg_dl structure outdated. |
| When that very same task will be dequeued later, put_prev_task_dl() will |
| then update the utilization, based on a wrong last_update_time, leading to |
| a huge spike in the DL utilization signal. |
| |
| The signal would eventually recover from this issue after few ms. Even |
| if no DL tasks are run, avg_dl is also updated in |
| __update_blocked_others(). But as the CPU capacity depends partly on the |
| avg_dl, 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 DL. |
| |
| Fixes: 3727e0e ("sched/dl: Add dl_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/1624271872-211872-3-git-send-email-vincent.donnefort@arm.com |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| kernel/sched/deadline.c | 2 ++ |
| 1 file changed, 2 insertions(+) |
| |
| diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c |
| index 8d06d1f4e2f7..6b98c1fe6e7f 100644 |
| --- a/kernel/sched/deadline.c |
| +++ b/kernel/sched/deadline.c |
| @@ -2470,6 +2470,8 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p) |
| check_preempt_curr_dl(rq, p, 0); |
| else |
| resched_curr(rq); |
| + } else { |
| + update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 0); |
| } |
| } |
| |
| -- |
| 2.30.2 |
| |