Guillaume Chazarain <guichaz@xxxxxxxx> wrote:
> FYI, I'm currently trying to track down where rq->clock started to
> overflow with nohz=off, and it seems to be before 2.6.23, so my patches
> are not at fault ;-) Or maybe I am dreaming and it was always
> overflowing. Investigating ...
And the winner is:
commit 529c77261bccd9d37f110f58b0753d95beaa9fa2
Author: Ingo Molnar <mingo@xxxxxxx>
Date: Fri Aug 10 23:05:11 2007 +0200
sched: improve rq-clock overflow logic
improve the rq-clock overflow logic: limit the absolute rq->clock
delta since the last scheduler tick, instead of limiting the delta
itself.
tested by Arjan van de Ven - whole laptop was misbehaving due to
an incorrectly calibrated cpu_khz confusing sched_clock().
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
diff --git a/kernel/sched.c b/kernel/sched.c
index b0afd8d..6247e4a 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -263,6 +263,7 @@ struct rq {
unsigned int clock_warps, clock_overflows;
unsigned int clock_unstable_events;
+ u64 tick_timestamp;
atomic_t nr_iowait;
@@ -341,8 +342,11 @@ static void __update_rq_clock(struct rq *rq)
/*
* Catch too large forward jumps too:
*/
- if (unlikely(delta > 2*TICK_NSEC)) {
- clock++;
+ if (unlikely(clock + delta > rq->tick_timestamp + TICK_NSEC)) {
+ if (clock < rq->tick_timestamp + TICK_NSEC)
+ clock = rq->tick_timestamp + TICK_NSEC;
+ else
+ clock++;
rq->clock_overflows++;
} else {
if (unlikely(delta > rq->clock_max_delta))
@@ -3308,9 +3312,16 @@ void scheduler_tick(void)
int cpu = smp_processor_id();
struct rq *rq = cpu_rq(cpu);
struct task_struct *curr = rq->curr;
+ u64 next_tick = rq->tick_timestamp + TICK_NSEC;
spin_lock(&rq->lock);
__update_rq_clock(rq);
+ /*
+ * Let rq->clock advance by at least TICK_NSEC:
+ */
+ if (unlikely(rq->clock < next_tick))
+ rq->clock = next_tick;
+ rq->tick_timestamp = rq->clock;
update_cpu_load(rq);
if (curr != rq->idle) /* FIXME: needed? */
curr->sched_class->task_tick(rq, curr);
Seems like I originally was not the only one seeing 2 jiffies jumps ;-)
I'll adapt my patches.
--
Guillaume
-
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