diff options
author | Thomas Gleixner <tglx@linutronix.de> | 2007-03-25 16:31:17 +0400 |
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committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-03-26 01:57:34 +0400 |
commit | 9501b6cf5541f0d576d566a463f1e7d3eaaab4eb (patch) | |
tree | 7983c4cc3c82e465cfe88a7fd67e39dbed72e1e0 /kernel/timer.c | |
parent | 317ec6cd00f25d05d153a780bc178c5335f320ee (diff) | |
download | linux-9501b6cf5541f0d576d566a463f1e7d3eaaab4eb.tar.xz |
[PATCH] dynticks: fix hrtimer rounding error in next_timer_interrupt
The rework of next_timer_interrupt() fixed the timer wheel bugs, but
invented a rounding error versus the next hrtimer event. This is caused
by the conversion of the hrtimer internal representation to relative
jiffies.
This causes bug #8100:
http://bugzilla.kernel.org/show_bug.cgi?id=8100
next_timer_interrupt() returns "now" in such a case and causes the code
in tick_nohz_stop_sched_tick() to trigger the timer softirq, which is
bogus as no timer is due for expiry. This results in an endless context
switching between idle and ksoftirqd until a timer is due for expiry.
Modify the hrtimer evaluation so that, it returns now + 1, when the
conversion results in a delta < 1 jiffie.
It's confirmed to resolve bug #8100
Reported-by: Emil Karlson <jkarlson@cc.hut.fi>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/timer.c')
-rw-r--r-- | kernel/timer.c | 19 |
1 files changed, 16 insertions, 3 deletions
diff --git a/kernel/timer.c b/kernel/timer.c index 797cccb86431..440048acaea1 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -695,15 +695,28 @@ static unsigned long cmp_next_hrtimer_event(unsigned long now, { ktime_t hr_delta = hrtimer_get_next_event(); struct timespec tsdelta; + unsigned long delta; if (hr_delta.tv64 == KTIME_MAX) return expires; - if (hr_delta.tv64 <= TICK_NSEC) - return now; + /* + * Expired timer available, let it expire in the next tick + */ + if (hr_delta.tv64 <= 0) + return now + 1; tsdelta = ktime_to_timespec(hr_delta); - now += timespec_to_jiffies(&tsdelta); + delta = timespec_to_jiffies(&tsdelta); + /* + * Take rounding errors in to account and make sure, that it + * expires in the next tick. Otherwise we go into an endless + * ping pong due to tick_nohz_stop_sched_tick() retriggering + * the timer softirq + */ + if (delta < 1) + delta = 1; + now += delta; if (time_before(now, expires)) return now; return expires; |