[PATCH 1/2] GetTimeInMillis: Use CLOCK_MONOTONIC_COARSE where available

[Daniel Stone]

On some systems, using CLOCK_MONOTONIC forces a readback of HPET or some
similarly expensive timer.  CLOCK_MONOTONIC_COARSE can alleviate this,
at the cost of negligibly-reduced resolution, so prefer that where we
can.

Signed-off-by: Daniel Stone <daniel at fooishbar.org>
---
 os/utils.c |   16 +++++++++++++++-
 1 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/os/utils.c b/os/utils.c
index afdff0c..18fd911 100644
--- a/os/utils.c
+++ b/os/utils.c
@@ -427,7 +427,21 @@ GetTimeInMillis(void)
 
 #ifdef MONOTONIC_CLOCK
     struct timespec tp;
-    if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0)
+    static clockid_t clockid;
+    if (!clockid) {
+#ifdef CLOCK_MONOTONIC_COARSE
+        if (clock_getres(CLOCK_MONOTONIC_COARSE, &tp) == 0 &&
+            (tp.tv_nsec / 1000) <= 1000 &&
+            clock_gettime(CLOCK_MONOTONIC_COARSE, &tp) == 0)
+            clockid = CLOCK_MONOTONIC_COARSE;
+        else
+#endif
+        if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0)
+            clockid = CLOCK_MONOTONIC;
+        else
+            clockid = ~0L;
+    }
+    if (clockid != ~0L && clock_gettime(clockid, &tp) == 0)
         return (tp.tv_sec * 1000) + (tp.tv_nsec / 1000000L);
 #endif
 
-- 
1.7.2.3