Re: [PATCH V3 1/3] sched/deadline: Replenishment timer should fire in the next period

[Wanpeng Li]

2017-02-28 18:07 GMT+08:00 Daniel Bristot de Oliveira :
> 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  49000   \
>--sched-deadline 5   \
>--sched-period  10 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 

>  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:
> -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 
> Reviewed-by: Luca Abeni 
> Reviewed-by: Steven Rostedt (VMware) 
> Reviewed-by: Juri Lelli 
> Cc: Ingo Molnar 
> Cc: Peter Zijlstra 
> Cc: Juri Lelli 
> Cc: Tommaso Cucinotta 
> Cc: Luca Abeni 
> Cc: Steven Rostedt 
> Cc: Mike Galbraith 
> Cc: Romulo Silva de Oliveira 
> Cc: Daniel Bristot de Oliveira 
> 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 70ef2b1..3c94d85 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
>

Re: [PATCH V3 1/3] sched/deadline: Replenishment timer should fire in the next period

[Wanpeng Li]

2017-02-28 18:07 GMT+08:00 Daniel Bristot de Oliveira :
> 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  49000   \
>--sched-deadline 5   \
>--sched-period  10 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 

>  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:
> -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 
> Reviewed-by: Luca Abeni 
> Reviewed-by: Steven Rostedt (VMware) 
> Reviewed-by: Juri Lelli 
> Cc: Ingo Molnar 
> Cc: Peter Zijlstra 
> Cc: Juri Lelli 
> Cc: Tommaso Cucinotta 
> Cc: Luca Abeni 
> Cc: Steven Rostedt 
> Cc: Mike Galbraith 
> Cc: Romulo Silva de Oliveira 
> Cc: Daniel Bristot de Oliveira 
> 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 70ef2b1..3c94d85 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
>

[PATCH V3 1/3] sched/deadline: Replenishment timer should fire in the next period

[Daniel Bristot de Oliveira]

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  49000   \
   --sched-deadline 5   \
   --sched-period  10 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.
 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:
-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 
Reviewed-by: Luca Abeni 
Reviewed-by: Steven Rostedt (VMware) 
Reviewed-by: Juri Lelli 
Cc: Ingo Molnar 
Cc: Peter Zijlstra 
Cc: Juri Lelli 
Cc: Tommaso Cucinotta 
Cc: Luca Abeni 
Cc: Steven Rostedt 
Cc: Mike Galbraith 
Cc: Romulo Silva de Oliveira 
Cc: Daniel Bristot de Oliveira 
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 70ef2b1..3c94d85 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

[PATCH V3 1/3] sched/deadline: Replenishment timer should fire in the next period

[Daniel Bristot de Oliveira]

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  49000   \
   --sched-deadline 5   \
   --sched-period  10 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.
 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:
-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 
Reviewed-by: Luca Abeni 
Reviewed-by: Steven Rostedt (VMware) 
Reviewed-by: Juri Lelli 
Cc: Ingo Molnar 
Cc: Peter Zijlstra 
Cc: Juri Lelli 
Cc: Tommaso Cucinotta 
Cc: Luca Abeni 
Cc: Steven Rostedt 
Cc: Mike Galbraith 
Cc: Romulo Silva de Oliveira 
Cc: Daniel Bristot de Oliveira 
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 70ef2b1..3c94d85 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