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-rw-r--r--kernel/timer.c17
1 files changed, 13 insertions, 4 deletions
diff --git a/kernel/timer.c b/kernel/timer.c
index 1433d87f46b..13e2b513be0 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1429,7 +1429,7 @@ static inline u64 time_interpolator_get_cycles(unsigned int src)
}
}
-static inline u64 time_interpolator_get_counter(void)
+static inline u64 time_interpolator_get_counter(int writelock)
{
unsigned int src = time_interpolator->source;
@@ -1443,6 +1443,15 @@ static inline u64 time_interpolator_get_counter(void)
now = time_interpolator_get_cycles(src);
if (lcycle && time_after(lcycle, now))
return lcycle;
+
+ /* When holding the xtime write lock, there's no need
+ * to add the overhead of the cmpxchg. Readers are
+ * force to retry until the write lock is released.
+ */
+ if (writelock) {
+ time_interpolator->last_cycle = now;
+ return now;
+ }
/* Keep track of the last timer value returned. The use of cmpxchg here
* will cause contention in an SMP environment.
*/
@@ -1456,7 +1465,7 @@ static inline u64 time_interpolator_get_counter(void)
void time_interpolator_reset(void)
{
time_interpolator->offset = 0;
- time_interpolator->last_counter = time_interpolator_get_counter();
+ time_interpolator->last_counter = time_interpolator_get_counter(1);
}
#define GET_TI_NSECS(count,i) (((((count) - i->last_counter) & (i)->mask) * (i)->nsec_per_cyc) >> (i)->shift)
@@ -1468,7 +1477,7 @@ unsigned long time_interpolator_get_offset(void)
return 0;
return time_interpolator->offset +
- GET_TI_NSECS(time_interpolator_get_counter(), time_interpolator);
+ GET_TI_NSECS(time_interpolator_get_counter(0), time_interpolator);
}
#define INTERPOLATOR_ADJUST 65536
@@ -1491,7 +1500,7 @@ static void time_interpolator_update(long delta_nsec)
* and the tuning logic insures that.
*/
- counter = time_interpolator_get_counter();
+ counter = time_interpolator_get_counter(1);
offset = time_interpolator->offset + GET_TI_NSECS(counter, time_interpolator);
if (delta_nsec < 0 || (unsigned long) delta_nsec < offset)