lkml.org 
[lkml]   [2006]   [Oct]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[patch 01/21] GTOD: exponential update_wall_time
From: John Stultz <johnstul@us.ibm.com>

Accumulate time in update_wall_time() exponentially. This avoids long
running loops seen with the dynticks patch as well as the problematic
hang seen on systems with broken clocksources.

NOTE: this only has relevance on dyntick kernels, so the quality of
NTP updates on jiffies-tick systems is unaffected. (non-dyntick
kernels call update_wall_time() in every timer tick)

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
--

kernel/timer.c | 28 ++++++++++++++++++++--------
1 file changed, 20 insertions(+), 8 deletions(-)
Index: linux-2.6.18-mm2/kernel/timer.c
===================================================================
--- linux-2.6.18-mm2.orig/kernel/timer.c 2006-10-02 00:55:50.000000000 +0200
+++ linux-2.6.18-mm2/kernel/timer.c 2006-10-02 00:55:50.000000000 +0200
@@ -907,6 +907,7 @@ static void clocksource_adjust(struct cl
static void update_wall_time(void)
{
cycle_t offset;
+ int shift = 0;

/* Make sure we're fully resumed: */
if (unlikely(timekeeping_suspended))
@@ -919,28 +920,39 @@ static void update_wall_time(void)
#endif
clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift;

+ while (offset > clock->cycle_interval << (shift + 1))
+ shift++;
+
/* normally this loop will run just once, however in the
* case of lost or late ticks, it will accumulate correctly.
*/
while (offset >= clock->cycle_interval) {
+ if (offset < (clock->cycle_interval << shift)) {
+ shift--;
+ continue;
+ }
+
/* accumulate one interval */
- clock->xtime_nsec += clock->xtime_interval;
- clock->cycle_last += clock->cycle_interval;
- offset -= clock->cycle_interval;
+ clock->xtime_nsec += clock->xtime_interval << shift;
+ clock->cycle_last += clock->cycle_interval << shift;
+ offset -= clock->cycle_interval << shift;

- if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
+ while (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
xtime.tv_sec++;
second_overflow();
}

/* interpolator bits */
- time_interpolator_update(clock->xtime_interval
- >> clock->shift);
+ time_interpolator_update((clock->xtime_interval
+ >> clock->shift)<<shift);

/* accumulate error between NTP and clock interval */
- clock->error += current_tick_length();
- clock->error -= clock->xtime_interval << (TICK_LENGTH_SHIFT - clock->shift);
+ clock->error += current_tick_length() << shift;
+ clock->error -= (clock->xtime_interval
+ << (TICK_LENGTH_SHIFT - clock->shift))<<shift;
+
+ shift--;
}

/* correct the clock when NTP error is too big */
--

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-10-02 01:09    [W:1.280 / U:0.552 seconds]
©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site