Reviewers: Benedikt Meurer, Sven Panne,
Message:
Use CLOCK_REALTIME_COARSE and CLOCK_MONOTONIC_COARSE when available for
reasons
of being faster than the traditional gettimeofday() and
clock_gettime(CLOCK_MONOTONIC) system calls.
As mentioned in CR 51333007, I can change the guard logic to `#if
defined(CLOCK_REALTIME_COARSE)` and `#if defined(CLOCK_MONOTONIC_COARSE)` so
Android gets it for free if/when they add support for it.
Description:
linux: use CLOCK_{REALTIME,MONOTONIC}_COARSE
Please review this at https://codereview.chromium.org/68203004/
Affected files (+41, -0 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..e3dae354203f12a591301a7e17770b1b2e684ec5
100644
--- a/src/platform/time.cc
+++ b/src/platform/time.cc
@@ -43,6 +43,15 @@
#include "win32-headers.h"
#endif
+#if V8_OS_LINUX && !V8_OS_ANDROID
+#if !defined(CLOCK_REALTIME_COARSE)
+#define CLOCK_REALTIME_COARSE 5 // 2.6.32 and up.
+#endif // !defined(CLOCK_REALTIME_COARSE)
+#if !defined(CLOCK_MONOTONIC_COARSE)
+#define CLOCK_MONOTONIC_COARSE 6 // 2.6.32 and up.
+#endif // !defined(CLOCK_MONOTONIC_COARSE)
+#endif // V8_OS_LINUX && !V8_OS_ANDROID
+
namespace v8 {
namespace internal {
@@ -271,11 +280,29 @@ FILETIME Time::ToFiletime() const {
#elif V8_OS_POSIX
Time Time::Now() {
+#if V8_OS_LINUX && !V8_OS_ANDROID
+ // Use CLOCK_REALTIME_COARSE if it's available and has a precision of 1
ms
+ // or higher. It's serviced from the vDSO with no system call overhead.
+ static clock_t clock_id = -1;
+ struct timespec ts;
+ if (clock_id == -1) {
+ if (clock_getres(CLOCK_REALTIME_COARSE, &ts) || ts.tv_nsec > 1000 *
1000) {
+ clock_id = CLOCK_REALTIME;
+ } else {
+ clock_id = CLOCK_REALTIME_COARSE;
+ }
+ }
+ int result = clock_gettime(clock_id, &ts);
+ ASSERT_EQ(0, result);
+ USE(result);
+ return FromTimespec(ts);
+#else // V8_OS_LINUX && !V8_OS_ANDROID
struct timeval tv;
int result = gettimeofday(&tv, NULL);
ASSERT_EQ(0, result);
USE(result);
return FromTimeval(tv);
+#endif // V8_OS_LINUX && !V8_OS_ANDROID
}
@@ -570,7 +597,21 @@ TimeTicks TimeTicks::HighResolutionNow() {
ticks = (tv.tv_sec * Time::kMicrosecondsPerSecond + tv.tv_usec);
#elif V8_OS_POSIX
struct timespec ts;
+#if V8_OS_LINUX && !V8_OS_ANDROID
+ // Use CLOCK_MONOTONIC_COARSE if it's available and has a precision of 1
ms
+ // or higher. It's serviced from the vDSO with no system call overhead.
+ static clock_t clock_id = -1;
+ if (clock_id == -1) {
+ if (clock_getres(CLOCK_MONOTONIC_COARSE, &ts) || ts.tv_nsec > 1000 *
1000) {
+ clock_id = CLOCK_MONOTONIC;
+ } else {
+ clock_id = CLOCK_MONOTONIC_COARSE;
+ }
+ }
+ int result = clock_gettime(clock_id, &ts);
+#else // V8_OS_LINUX && !V8_OS_ANDROID
int result = clock_gettime(CLOCK_MONOTONIC, &ts);
+#endif // V8_OS_LINUX && !V8_OS_ANDROID
ASSERT_EQ(0, result);
USE(result);
ticks = (ts.tv_sec * Time::kMicrosecondsPerSecond +
--
--
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