Reviewers: ,
Message:
Use clock_gettime(CLOCK_MONOTONIC_COARSE) if available, saves the overhead
of a
system call on older and virtualized systems.
Description:
linux: use CLOCK_MONOTONIC_COARSE
Please review this at https://codereview.chromium.org/51333007/
Affected files (+34, -1 lines):
M src/platform/time.cc
Index: src/platform/time.cc
diff --git a/src/platform/time.cc b/src/platform/time.cc
index
de0ca16473f6b5106485508653cfe797f6632c37..a6c426f62db48c4e71f18b4b5789744baf1c597a
100644
--- a/src/platform/time.cc
+++ b/src/platform/time.cc
@@ -28,6 +28,7 @@
#include "platform/time.h"
#if V8_OS_POSIX
+#include <errno.h>
#include <sys/time.h>
#endif
#if V8_OS_MACOSX
@@ -270,6 +271,8 @@ FILETIME Time::ToFiletime() const {
#elif V8_OS_POSIX
+// OS X doesn't support POSIX high-res timers and Solaris uses gethrtime().
+#if V8_OS_MACOSX || V8_OS_SOLARIS
Time Time::Now() {
struct timeval tv;
int result = gettimeofday(&tv, NULL);
@@ -277,6 +280,36 @@ Time Time::Now() {
USE(result);
return FromTimeval(tv);
}
+#else
+inline int GetBestMonotonicClock(struct timespec* ts) {
+#if V8_OS_LINUX
+ // Prefer CLOCK_MONOTONIC_COARSE. It's a high-res clock that's
available as
+ // of 2.6.32. It can be fully serviced from the vDSO, even on
virtualized
+ // systems, which saves the overhead of a system call. The coarseness
is not
+ // an issue for us because it still has sub-microsecond resolution.
+ static bool no_clock_monotonic_coarse;
+ if (no_clock_monotonic_coarse == false) {
+ if (clock_gettime(6 /* CLOCK_MONOTONIC_COARSE */, ts) == 0) {
+ return 0;
+ }
+ if (errno != EINVAL) {
+ return -1;
+ }
+ no_clock_monotonic_coarse = true;
+ }
+#endif // V8_OS_LINUX
+ return clock_gettime(CLOCK_MONOTONIC, ts);
+}
+
+
+Time Time::Now() {
+ struct timespec ts;
+ int result = GetBestMonotonicClock(&ts);
+ ASSERT_EQ(0, result);
+ USE(result);
+ return FromTimespec(ts);
+}
+#endif // V8_OS_MACOSX || V8_OS_SOLARIS
Time Time::NowFromSystemTime() {
@@ -570,7 +603,7 @@ TimeTicks TimeTicks::HighResolutionNow() {
ticks = (tv.tv_sec * Time::kMicrosecondsPerSecond + tv.tv_usec);
#elif V8_OS_POSIX
struct timespec ts;
- int result = clock_gettime(CLOCK_MONOTONIC, &ts);
+ int result = GetBestMonotonicClock(&ts);
ASSERT_EQ(0, result);
USE(result);
ticks = (ts.tv_sec * Time::kMicrosecondsPerSecond +
--
--
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