Greetings,
I've broken down my throttling tree into 6 patches, which I'll send as
replies to this start-point.
Patch 1/6
Ignore timewarps caused by SMP timestamp rounding. Also, don't stamp a
task with a computed timestamp, stamp with the already called clock.
Signed-off-by: Mike Galbraith <[email protected]>
--- linux-2.6.16-mm1/kernel/sched.c.org 2006-03-23 15:01:41.000000000 +0100
+++ linux-2.6.16-mm1/kernel/sched.c 2006-03-23 15:02:25.000000000 +0100
@@ -805,6 +805,16 @@
unsigned long long __sleep_time = now - p->timestamp;
unsigned long sleep_time;
+ /*
+ * On SMP systems, a task can go to sleep on one CPU and
+ * wake up on another. When this happens, the timestamp
+ * is rounded to the nearest tick, which can lead to now
+ * being less than p->timestamp for short sleeps. Ignore
+ * these, they're insignificant.
+ */
+ if (unlikely(now < p->timestamp))
+ __sleep_time = 0ULL;
+
if (batch_task(p))
sleep_time = 0;
else {
@@ -871,20 +881,20 @@
*/
static void activate_task(task_t *p, runqueue_t *rq, int local)
{
- unsigned long long now;
+ unsigned long long now, comp;
- now = sched_clock();
+ now = comp = sched_clock();
#ifdef CONFIG_SMP
if (!local) {
/* Compensate for drifting sched_clock */
runqueue_t *this_rq = this_rq();
- now = (now - this_rq->timestamp_last_tick)
+ comp = (now - this_rq->timestamp_last_tick)
+ rq->timestamp_last_tick;
}
#endif
if (!rt_task(p))
- p->prio = recalc_task_prio(p, now);
+ p->prio = recalc_task_prio(p, comp);
/*
* This checks to make sure it's not an uninterruptible task
-
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