diff options
authorLuca Abeni <luca.abeni@unitn.it>2014-12-17 11:50:32 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-01-16 06:59:33 -0800
commitcae817ad60ef1a615dcdb0dd7dc505aefe63c88c (patch)
parent678c8bb7aa75fb956b311b42ad4b7262bcc24b5e (diff)
sched/deadline: Avoid double-accounting in case of missed deadlines
commit 269ad8015a6b2bb1cf9e684da4921eb6fa0a0c88 upstream. The dl_runtime_exceeded() function is supposed to ckeck if a SCHED_DEADLINE task must be throttled, by checking if its current runtime is <= 0. However, it also checks if the scheduling deadline has been missed (the current time is larger than the current scheduling deadline), further decreasing the runtime if this happens. This "double accounting" is wrong: - In case of partitioned scheduling (or single CPU), this happens if task_tick_dl() has been called later than expected (due to small HZ values). In this case, the current runtime is also negative, and replenish_dl_entity() can take care of the deadline miss by recharging the current runtime to a value smaller than dl_runtime - In case of global scheduling on multiple CPUs, scheduling deadlines can be missed even if the task did not consume more runtime than expected, hence penalizing the task is wrong This patch fix this problem by throttling a SCHED_DEADLINE task only when its runtime becomes negative, and not modifying the runtime Signed-off-by: Luca Abeni <luca.abeni@unitn.it> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Juri Lelli <juri.lelli@gmail.com> Cc: Dario Faggioli <raistlin@linux.it> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1418813432-20797-3-git-send-email-luca.abeni@unitn.it Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 1 insertions, 18 deletions
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index b3228b9647f0..8d3c5ddfdfdd 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -550,24 +550,7 @@ void init_dl_task_timer(struct sched_dl_entity *dl_se)
int dl_runtime_exceeded(struct rq *rq, struct sched_dl_entity *dl_se)
- int dmiss = dl_time_before(dl_se->deadline, rq_clock(rq));
- int rorun = dl_se->runtime <= 0;
- if (!rorun && !dmiss)
- return 0;
- /*
- * If we are beyond our current deadline and we are still
- * executing, then we have already used some of the runtime of
- * the next instance. Thus, if we do not account that, we are
- * stealing bandwidth from the system at each deadline miss!
- */
- if (dmiss) {
- dl_se->runtime = rorun ? dl_se->runtime : 0;
- dl_se->runtime -= rq_clock(rq) - dl_se->deadline;
- }
- return 1;
+ return (dl_se->runtime <= 0);
extern bool sched_rt_bandwidth_account(struct rt_rq *rt_rq);