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Measure timer resolution

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Add code to measure timer resolution on POSIX systems

Change-Id: I980f7e416725effe1872f2c5e75805d753e3b0ae
Reviewed-on: https://chromium-review.googlesource.com/1086994
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53552}
This commit is contained in:
Ivica Bogosavljevic 2018-06-06 13:53:50 +02:00 committed by Commit Bot
parent 3c4d0316e4
commit 670c96d3b5
1 changed files with 30 additions and 1 deletions
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31
src/base/platform/time.cc
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@ -86,6 +86,26 @@ V8_INLINE int64_t ClockNow(clockid_t clk_id) {
return 0;
#endif
}
V8_INLINE bool IsHighResolutionTimer(clockid_t clk_id) {
// Limit duration of timer resolution measurement to 100 ms. If we cannot
// measure timer resoltuion within this time, we assume a low resolution
// timer.
int64_t end =
ClockNow(clk_id) + 100 * v8::base::Time::kMicrosecondsPerMillisecond;
int64_t start, delta;
do {
start = ClockNow(clk_id);
// Loop until we can detect that the clock has changed. Non-HighRes timers
// will increment in chunks, i.e. 15ms. By spinning until we see a clock
// change, we detect the minimum time between measurements.
do {
delta = ClockNow(clk_id) - start;
} while (delta == 0);
} while (delta > 1 && start < end);
return delta <= 1;
}
#elif V8_OS_WIN
V8_INLINE bool IsQPCReliable() {
v8::base::CPU cpu;
@ -735,7 +755,16 @@ TimeTicks TimeTicks::Now() {
}
// static
bool TimeTicks::IsHighResolution() { return true; }
bool TimeTicks::IsHighResolution() {
#if V8_OS_MACOSX
return true;
#elif V8_OS_POSIX
static bool is_high_resolution = IsHighResolutionTimer(CLOCK_MONOTONIC);
return is_high_resolution;
#else
return true;
#endif
}
#endif // V8_OS_WIN