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updating the utilization when the rq starts running DL tasks, will not see a such change, leaving the avg_dl structure outdated.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.donnefo... 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); } }