Messages in this thread Patch in this message | | | Date | Sat, 12 Jan 2008 01:03:53 +0100 | From | Guillaume Chazarain <> | Subject | Re: CONFIG_NO_HZ breaks blktrace timestamps |
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Guillaume Chazarain <guichaz@yahoo.fr> 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@elte.hu> 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@elte.hu> Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
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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