Messages in this thread Patch in this message | | | From | Dietmar Eggemann <> | Subject | [PATCH v2 1/3] sched/deadline: Fix double accounting of rq/running bw in push & pull | Date | Fri, 2 Aug 2019 15:59:43 +0100 |
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[push/pull]_dl_task() always call deactivate_task() with flags=0 which sets p->on_rq=TASK_ON_RQ_MIGRATING.
[push/pull]_dl_task()->deactivate_task()->dequeue_task()-> dequeue_task_dl() calls sub_[running/rq]_bw() since p->on_rq=TASK_ON_RQ_MIGRATING. So sub_[running/rq]_bw() in [push/pull]_dl_task() is double-accounting for that task.
The same goes for add_[rq/running]_bw() and activate_task().
[push/pull]_dl_task()->activate_task()->enqueue_task()-> enqueue_task_dl() calls add_[rq/running]_bw() again since p->on_rq is still set to TASK_ON_RQ_MIGRATING. So the add_[rq/running]_bw() in enqueue_task_dl() is double-accounting for that task.
Fix it by removing rq/running bw accounting in [push/pull]_dl_task().
Trace (CONFIG_SCHED_DEBUG=y) before the fix on a 6 CPUs system with 6 DL (12000/100000/100000) tasks showing the issue:
[ 48.147868] dl_rq->running_bw > old [ 48.147886] WARNING: CPU: 1 PID: 0 at kernel/sched/deadline.c:98 ... [ 48.274832] inactive_task_timer+0x468/0x4e8 [ 48.279057] __hrtimer_run_queues+0x10c/0x3b8 [ 48.283364] hrtimer_interrupt+0xd4/0x250 [ 48.287330] tick_handle_oneshot_broadcast+0x198/0x1d0 ... [ 48.360057] dl_rq->running_bw > dl_rq->this_bw [ 48.360065] WARNING: CPU: 1 PID: 0 at kernel/sched/deadline.c:86 ... [ 48.488294] task_contending+0x1a0/0x208 [ 48.492172] enqueue_task_dl+0x3b8/0x970 [ 48.496050] activate_task+0x70/0xd0 [ 48.499584] ttwu_do_activate+0x50/0x78 [ 48.503375] try_to_wake_up+0x270/0x7a0 [ 48.507167] wake_up_process+0x14/0x20 [ 48.510873] hrtimer_wakeup+0x1c/0x30 ... [ 50.062867] dl_rq->this_bw > old [ 50.062885] WARNING: CPU: 1 PID: 2048 at kernel/sched/deadline.c:122 ... [ 50.190520] dequeue_task_dl+0x1e4/0x1f8 [ 50.194400] __sched_setscheduler+0x1d0/0x860 [ 50.198707] _sched_setscheduler+0x74/0x98 [ 50.202757] do_sched_setscheduler+0xa8/0x110 [ 50.207065] __arm64_sys_sched_setscheduler+0x1c/0x30
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Fixes: 7dd778841164 ("sched/core: Unify p->on_rq updates") --- kernel/sched/deadline.c | 8 -------- 1 file changed, 8 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 039dde2b1dac..6dafaabde1d6 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -2121,17 +2121,13 @@ static int push_dl_task(struct rq *rq) } deactivate_task(rq, next_task, 0); - sub_running_bw(&next_task->dl, &rq->dl); - sub_rq_bw(&next_task->dl, &rq->dl); set_task_cpu(next_task, later_rq->cpu); - add_rq_bw(&next_task->dl, &later_rq->dl); /* * Update the later_rq clock here, because the clock is used * by the cpufreq_update_util() inside __add_running_bw(). */ update_rq_clock(later_rq); - add_running_bw(&next_task->dl, &later_rq->dl); activate_task(later_rq, next_task, ENQUEUE_NOCLOCK); ret = 1; @@ -2219,11 +2215,7 @@ static void pull_dl_task(struct rq *this_rq) resched = true; deactivate_task(src_rq, p, 0); - sub_running_bw(&p->dl, &src_rq->dl); - sub_rq_bw(&p->dl, &src_rq->dl); set_task_cpu(p, this_cpu); - add_rq_bw(&p->dl, &this_rq->dl); - add_running_bw(&p->dl, &this_rq->dl); activate_task(this_rq, p, 0); dmin = p->dl.deadline; -- 2.17.1
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