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Date: Mon, 18 Dec 2017 16:48:15 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Daniel Bristot de Oliveira <bristot@...hat.com>, "Peter Zijlstra (Intel)" <peterz@...radead.org>, Luca Abeni <luca.abeni@...tannapisa.it>, "Steven Rostedt (VMware)" <rostedt@...dmis.org>, Juri Lelli <juri.lelli@....com>, Linus Torvalds <torvalds@...ux-foundation.org>, Mike Galbraith <efault@....de>, Romulo Silva de Oliveira <romulo.deoliveira@...c.br>, Thomas Gleixner <tglx@...utronix.de>, Tommaso Cucinotta <tommaso.cucinotta@...up.it>, Ingo Molnar <mingo@...nel.org>, Sasha Levin <alexander.levin@...izon.com> Subject: [PATCH 4.9 072/177] sched/deadline: Make sure the replenishment timer fires in the next period 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Daniel Bristot de Oliveira <bristot@...hat.com> [ Upstream commit 5ac69d37784b237707a7b15d199cdb6c6fdb6780 ] 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: 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@...hat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org> Reviewed-by: Luca Abeni <luca.abeni@...tannapisa.it> Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org> Reviewed-by: Juri Lelli <juri.lelli@....com> Cc: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Mike Galbraith <efault@....de> Cc: Peter Zijlstra <peterz@...radead.org> Cc: Romulo Silva de Oliveira <romulo.deoliveira@...c.br> Cc: Steven Rostedt <rostedt@...dmis.org> Cc: Thomas Gleixner <tglx@...utronix.de> Cc: Tommaso Cucinotta <tommaso.cucinotta@...up.it> Link: http://lkml.kernel.org/r/ac50d89887c25285b47465638354b63362f8adff.1488392936.git.bristot@redhat.com Signed-off-by: Ingo Molnar <mingo@...nel.org> Signed-off-by: Sasha Levin <alexander.levin@...izon.com> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- kernel/sched/deadline.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -505,10 +505,15 @@ static void update_dl_entity(struct sche } } +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_st * 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);
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