Replace the usage of MACH monotonic function 'clock_get_time' with 'mach_absolute_time' in GetTickCount64.

Monotonic clock function 'clock_get_time' was causing perf regression in 'Environment.TickCount'. So replacing it with 'mach_absolute_time' which gives considerable performance gains. Here are the perf numbers
Using 'clock_get_time' (without caching host ports) - Average time 2.86 microseconds.
Using 'clock_get_time' (with caching host ports) - Average time 0.82 microseconds.
Using 'gettimeofday' (original implementation) - Average time 0.05 microseconds.
Using 'mach_absolute_time' - Average time 0.04 microseconds.

3 files changed, 23 insertions, 31 deletions

diff --git a/src/pal/src/config.h.in b/src/pal/src/config.h.in
index c267a39556..354f455bf4 100644
--- a/src/pal/src/config.h.in
+++ b/src/pal/src/config.h.in
@@ -85,7 +85,7 @@
 #cmakedefine01 HAVE_WORKING_GETTIMEOFDAY
 #cmakedefine01 HAVE_WORKING_CLOCK_GETTIME
 #cmakedefine01 HAVE_CLOCK_MONOTONIC
-#cmakedefine01 HAVE_MACH_CLOCK_MONOTONIC
+#cmakedefine01 HAVE_MACH_ABSOLUTE_TIME
 #cmakedefine01 STATVFS64_PROTOTYPE_BROKEN
 #cmakedefine01 HAVE_MMAP_DEV_ZERO
 #cmakedefine01 MMAP_IGNORES_HINT
diff --git a/src/pal/src/configure.cmake b/src/pal/src/configure.cmake
index dce3ef4c44..bc3d0c83b9 100644
--- a/src/pal/src/configure.cmake
+++ b/src/pal/src/configure.cmake
@@ -328,18 +328,16 @@ int main()
 }" HAVE_CLOCK_MONOTONIC)
 check_cxx_source_runs("
 #include <stdlib.h>
-#include <mach/mach.h>
-#include <mach/clock.h>
+#include <mach/mach_time.h>
 
 int main()
 {
   int ret;
-  clock_serv_t clock;
-  mach_timespec_t mts;
-  host_get_clock_service(mach_host_self(), SYSTEM_CLOCK, &clock);
-  ret = clock_get_time(clock, &mts);
+  mach_timebase_info_data_t timebaseInfo;
+  ret = mach_timebase_info(&timebaseInfo);
+  mach_absolute_time();
   exit(ret);
-}" HAVE_MACH_CLOCK_MONOTONIC)
+}" HAVE_MACH_ABSOLUTE_TIME)
 check_cxx_source_runs("
 #include <stdlib.h>
 #include <sys/types.h>
diff --git a/src/pal/src/misc/time.cpp b/src/pal/src/misc/time.cpp
index d5065dbd37..be875a4487 100644
--- a/src/pal/src/misc/time.cpp
+++ b/src/pal/src/misc/time.cpp
@@ -28,13 +28,16 @@ Abstract:
 #include <errno.h>
 #include <string.h>
 
-#if HAVE_MACH_CLOCK_MONOTONIC
-#include <mach/mach.h>
-#include <mach/clock.h>
+#if HAVE_MACH_ABSOLUTE_TIME
+#include <mach/mach_time.h>
+static mach_timebase_info_data_t s_TimebaseInfo;
 #endif
 
 SET_DEFAULT_DEBUG_CHANNEL(MISC);
 
+
+
+
 /*++
 Function:
   GetSystemTime
@@ -275,28 +278,19 @@ GetTickCount64()
         }
         retval = (ts.tv_sec * tccSecondsToMillieSeconds)+(ts.tv_nsec / tccMillieSecondsToNanoSeconds);
     }
-#elif HAVE_MACH_CLOCK_MONOTONIC
+#elif HAVE_MACH_ABSOLUTE_TIME
     {
-        kern_return_t machRet;
-        clock_serv_t clock;
-        mach_timespec_t mts;
-        host_t host = mach_host_self();
-
-        if((machRet = host_get_clock_service(host, SYSTEM_CLOCK, &clock)) != KERN_SUCCESS)
-        {
-            ASSERT("host_get_clock_service() failed: %s\n", mach_error_string(machRet));
-            goto EXIT;
-        }
-        machRet = clock_get_time(clock, &mts);
-        mach_port_deallocate(mach_task_self(), host);
-        mach_port_deallocate(mach_task_self(), clock);
-
-        if(machRet != KERN_SUCCESS)
+        // use denom == 0 to indicate that s_TimebaseInfo is uninitialised.
+        if (s_TimebaseInfo.denom == 0)
         {
-            ASSERT("clock_get_time() failed: %s\n", mach_error_string(machRet));
-            goto EXIT;
+            kern_return_t machRet;
+            if((machRet = mach_timebase_info(&s_TimebaseInfo)) != KERN_SUCCESS)
+            {
+                ASSERT("mach_timebase_info() failed: %s\n", mach_error_string(machRet));
+                goto EXIT;
+            }
         }
-        retval = (mts.tv_sec * tccSecondsToMillieSeconds)+(mts.tv_nsec / tccMillieSecondsToNanoSeconds);
+        retval = (mach_absolute_time() * s_TimebaseInfo.numer / s_TimebaseInfo.denom) / tccMillieSecondsToNanoSeconds;
     }
 #elif HAVE_GETHRTIME
     {
@@ -326,4 +320,4 @@ GetTickCount64()
 #endif // HAVE_CLOCK_MONOTONIC 
 EXIT:    
     return retval;
-}
+}
\ No newline at end of file