On 2019/3/13 22:49, luca abeni wrote:
Hi, After looking at the patch a little bit more and running some tests, I suspect this solution might be racy: when the timer is already active, (and hrtimer_start() fails), it relies on its handler to decrease the running bw (by setting dl_non_contending to 1)... But inactive_task_timer() might have already checked dl_non_contending, finding it equal to 0 (so, it ends up doing nothing and the running bw is not decreased). So, I would prefer a different solution. I think this patch should work: diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 6a73e41a2016..43901fa3f269 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -252,7 +252,6 @@ static void task_non_contending(struct task_struct *p) if (dl_entity_is_special(dl_se)) return;- WARN_ON(hrtimer_active(&dl_se->inactive_timer));WARN_ON(dl_se->dl_non_contending);zerolag_time = dl_se->deadline -@@ -269,7 +268,7 @@ static void task_non_contending(struct task_struct *p) * If the "0-lag time" already passed, decrease the active * utilization now, instead of starting a timer */ - if (zerolag_time < 0) { + if ((zerolag_time < 0) || hrtimer_active(&dl_se->inactive_timer)) { if (dl_task(p)) sub_running_bw(dl_se, dl_rq); if (!dl_task(p) || p->state == TASK_DEAD) { The idea is that if the timer is active, we leave dl_non_contending set to 0 (so that the timer handler does nothing), and we immediately decrease the running bw. I think this is OK, because this situation can happen only if the task blocks, wakes up while the timer handler is running, and then immediately blocks again - while the timer handler is still running. So, the "zero lag time" cannot be too much in the future. Thanks, Luca .
Yeah, it looks good. I can do some experiments with it , Do you have some testcases to help me with the test ? Thanks, Cheng Jian.
