1 files changed, 13 insertions, 4 deletions

diff --git a/kernel/timer.c b/kernel/timer.c
index 1433d87f46b3..13e2b513be01 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)