Messages in this thread | | | Date | Fri, 26 Jul 2019 12:11:59 +0200 | From | luca abeni <> | Subject | Re: [PATCH 1/5] sched/deadline: Fix double accounting of rq/running bw in push_dl_task() |
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Hi Dietmar,
On Fri, 26 Jul 2019 09:27:52 +0100 Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
> push_dl_task() always calls deactivate_task() with flags=0 which sets > p->on_rq=TASK_ON_RQ_MIGRATING.
Uhm... This is a recent change in the deactivate_task() behaviour, right? Because I tested SCHED_DEADLINE a lot, but I've never seen this issue :)
Anyway, looking at the current code the change looks OK. Thanks for fixing this issue!
Luca
> push_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_dl_task() is double-accounting for > that task. > > The same is true for add_[rq/running]_bw() and activate_task() on the > destination (later) CPU. > push_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 this by removing the rq/running bw accounting in push_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> > --- > kernel/sched/deadline.c | 4 ---- > 1 file changed, 4 deletions(-) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index de2bd006fe93..d1aeada374e1 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; >
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