sched: SCHED_FIFO/SCHED_RR watchdog timer

Introduce a new rlimit that allows the user to set a runtime timeout on
real-time tasks their slice. Once this limit is exceeded the task will receive
SIGXCPU.

So it measures runtime since the last sleep.

Input and ideas by Thomas Gleixner and Lennart Poettering.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Lennart Poettering <mzxreary@0pointer.de>
CC: Michael Kerrisk <mtk.manpages@googlemail.com>
CC: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 30 insertions, 0 deletions

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 29963af..f350f7b 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -116,6 +116,9 @@ static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)
 	inc_cpu_load(rq, p->se.load.weight);
 
 	inc_rt_tasks(p, rq);
+
+	if (wakeup)
+		p->rt.timeout = 0;
 }
 
 /*
@@ -834,11 +837,38 @@ static void prio_changed_rt(struct rq *rq, struct task_struct *p,
 	}
 }
 
+static void watchdog(struct rq *rq, struct task_struct *p)
+{
+	unsigned long soft, hard;
+
+	if (!p->signal)
+		return;
+
+	soft = p->signal->rlim[RLIMIT_RTTIME].rlim_cur;
+	hard = p->signal->rlim[RLIMIT_RTTIME].rlim_max;
+
+	if (soft != RLIM_INFINITY) {
+		unsigned long next;
+
+		p->rt.timeout++;
+		next = DIV_ROUND_UP(min(soft, hard), USEC_PER_SEC/HZ);
+		if (next > p->rt.timeout) {
+			u64 next_time = p->se.sum_exec_runtime;
+
+			next_time += next * (NSEC_PER_SEC/HZ);
+			if (p->it_sched_expires > next_time)
+				p->it_sched_expires = next_time;
+		} else
+			p->it_sched_expires = p->se.sum_exec_runtime;
+	}
+}
 
 static void task_tick_rt(struct rq *rq, struct task_struct *p)
 {
 	update_curr_rt(rq);
 
+	watchdog(rq, p);
+
 	/*
 	 * RR tasks need a special form of timeslice management.
 	 * FIFO tasks have no timeslices.