Messages in this thread | | | From | Wanpeng Li <> | Date | Tue, 7 Mar 2017 15:51:24 +0800 | Subject | Re: [PATCH V4 1/3] sched/deadline: Replenishment timer should fire in the next period |
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2017-03-02 22:10 GMT+08:00 Daniel Bristot de Oliveira <bristot@redhat.com>: > Currently, the replenishment timer is set to fire at the deadline > of a task. Although that works for implicit deadline tasks because the > deadline is equals to the begin of the next period, that is not correct > for constrained deadline tasks (deadline < period). > > For instance: > > f.c: > --------------- %< --------------- > int main (void) > { > for(;;); > } > --------------- >% --------------- > > # gcc -o f f.c > > # trace-cmd record -e sched:sched_switch \ > -e syscalls:sys_exit_sched_setattr \ > chrt -d --sched-runtime 490000000 \ > --sched-deadline 500000000 \ > --sched-period 1000000000 0 ./f > > # trace-cmd report | grep "{pid of ./f}" > > After setting parameters, the task is replenished and continue running > until being throttled. > f-11295 [003] 13322.113776: sys_exit_sched_setattr: 0x0 > > The task is throttled after running 492318 ms, as expected.
This should be us.
Otherwise,
Reviewed-by: Wanpeng Li <wanpeng.li@hotmail.com>
> f-11295 [003] 13322.606094: sched_switch: f:11295 [-1] R ==> \ > watchdog/3:32 [0] > > But then, the task is replenished 500719 ms after the first > replenishment: > <idle>-0 [003] 13322.614495: sched_switch: swapper/3:0 [120] R \ > ==> f:11295 [-1] > > Running for 490277 ms: > f-11295 [003] 13323.104772: sched_switch: f:11295 [-1] R ==> \ > swapper/3:0 [120] > > Hence, in the first period, the task runs 2 * runtime, and that is a bug. > > During the first replenishment, the next deadline is set one period away. > So the runtime / period starts to be respected. However, as the second > replenishment took place in the wrong instant, the next replenishment > will also be held in a wrong instant of time. Rather than occurring in > the nth period away from the first activation, it is taking place > in the (nth period - relative deadline). > > Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com> > Reviewed-by: Luca Abeni <luca.abeni@santannapisa.it> > Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org> > Reviewed-by: Juri Lelli <juri.lelli@arm.com> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Juri Lelli <juri.lelli@arm.com> > Cc: Tommaso Cucinotta <tommaso.cucinotta@sssup.it> > Cc: Luca Abeni <luca.abeni@santannapisa.it> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Mike Galbraith <efault@gmx.de> > Cc: Romulo Silva de Oliveira <romulo.deoliveira@ufsc.br> > Cc: Daniel Bristot de Oliveira <bristot@redhat.com> > Cc: linux-kernel@vger.kernel.org > --- > kernel/sched/deadline.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index 27737f3..3e3caae 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -505,10 +505,15 @@ static void update_dl_entity(struct sched_dl_entity *dl_se, > } > } > > +static inline u64 dl_next_period(struct sched_dl_entity *dl_se) > +{ > + return dl_se->deadline - dl_se->dl_deadline + dl_se->dl_period; > +} > + > /* > * If the entity depleted all its runtime, and if we want it to sleep > * while waiting for some new execution time to become available, we > - * set the bandwidth enforcement timer to the replenishment instant > + * set the bandwidth replenishment timer to the replenishment instant > * and try to activate it. > * > * Notice that it is important for the caller to know if the timer > @@ -530,7 +535,7 @@ static int start_dl_timer(struct task_struct *p) > * that it is actually coming from rq->clock and not from > * hrtimer's time base reading. > */ > - act = ns_to_ktime(dl_se->deadline); > + act = ns_to_ktime(dl_next_period(dl_se)); > now = hrtimer_cb_get_time(timer); > delta = ktime_to_ns(now) - rq_clock(rq); > act = ktime_add_ns(act, delta); > -- > 2.9.3 >
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