Messages in this thread Patch in this message | | | Date | Thu, 18 Nov 2021 16:20:17 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH -next 1/1] sched/rt: Try to restart rt period timer when rt runtime exceeded |
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On Mon, Nov 15, 2021 at 01:46:28AM +0000, Li Hua wrote: > When rt_runtime is modified from -1 to a valid control value, it may > cause the task to be throttled all the time. Operations like the following > will trigger the bug. E.g: > 1. echo -1 > /proc/sys/kernel/sched_rt_runtime_us > 2. Run a FIFO task named A that executes while(1) > 3. echo 950000 > /proc/sys/kernel/sched_rt_runtime_us > > When rt_runtime is -1, The rt period timer will not be activated when task A > enqueued. And then the task will be throttled after setting rt_runtime to > 950,000. The task will always be throttled because the rt period timer is not > activated. > > Reported-by: Hulk Robot <hulkci@huawei.com> > Signed-off-by: Li Hua <hucool.lihua@huawei.com> > --- > kernel/sched/rt.c | 26 +++++++++++++++++++++++++- > 1 file changed, 25 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index bb945f8faeca..630f2cbe37d0 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -947,6 +947,23 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se) > return rt_task_of(rt_se)->prio; > } > > +static inline void try_start_rt_bandwidth(struct rt_bandwidth *rt_b) > +{ > + raw_spin_lock(&rt_b->rt_runtime_lock); > + if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF) { > + raw_spin_unlock(&rt_b->rt_runtime_lock); > + return; > + } > + > + if (!rt_b->rt_period_active) { > + rt_b->rt_period_active = 1; > + hrtimer_forward_now(&rt_b->rt_period_timer, rt_b->rt_period); > + hrtimer_start_expires(&rt_b->rt_period_timer, > + HRTIMER_MODE_ABS_PINNED_HARD); > + } > + raw_spin_unlock(&rt_b->rt_runtime_lock); > +}
This is almost a verbatim copy of start_rt_bandwidth() surely we can do better.
> + > static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq) > { > u64 runtime = sched_rt_runtime(rt_rq); > @@ -1027,11 +1044,16 @@ static void update_curr_rt(struct rq *rq) > struct rt_rq *rt_rq = rt_rq_of_se(rt_se); > > if (sched_rt_runtime(rt_rq) != RUNTIME_INF) { > + int exceeded; > + > raw_spin_lock(&rt_rq->rt_runtime_lock); > rt_rq->rt_time += delta_exec; > - if (sched_rt_runtime_exceeded(rt_rq)) > + exceeded = sched_rt_runtime_exceeded(rt_rq); > + if (exceeded) > resched_curr(rq); > raw_spin_unlock(&rt_rq->rt_runtime_lock); > + if (exceeded) > + try_start_rt_bandwidth(sched_rt_bandwidth(rt_rq)); > } > } > } > @@ -2905,8 +2927,10 @@ static int sched_rt_global_validate(void) > > static void sched_rt_do_global(void) > { > + raw_spin_lock(&def_rt_bandwidth.rt_runtime_lock); > def_rt_bandwidth.rt_runtime = global_rt_runtime(); > def_rt_bandwidth.rt_period = ns_to_ktime(global_rt_period()); > + raw_spin_unlock(&def_rt_bandwidth.rt_runtime_lock);
And that's just wrong I think; did you test this with lockdep enabled? IIRC this lock is irq-safe, it has to be if you're using it form a timer context.
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