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Bug 784859 - Part 1: Use QueryPerformanceCounter directly if the machine has a stable TSC; r=bbondy

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This commit is contained in:
Ehsan Akhgari 2012-09-06 11:01:06 -04:00
parent d12e45081e
commit cdd36264b3
1 changed files with 26 additions and 0 deletions
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26
xpcom/ds/TimeStamp_windows.cpp
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@ -24,6 +24,25 @@
#include "prlog.h"
#include <stdio.h>
#include <intrin.h>
static bool
HasStableTSC()
{
int regs[4];
// detect if the Advanced Power Management feature is supported
__cpuid(regs, 0x80000000);
if (regs[0] < 0x80000007)
return false;
__cpuid(regs, 0x80000007);
// if bit 8 is set than TSC will run at a constant rate
// in all ACPI P-state, C-states and T-states
return regs[3] & (1 << 8);
}
#if defined(PR_LOGGING)
// Log module for mozilla::TimeStamp for Windows logging...
//
@ -47,6 +66,8 @@ static const double kNsPerSecd = 1000000000.0;
static const LONGLONG kNsPerSec = 1000000000;
static const LONGLONG kNsPerMillisec = 1000000;
static bool sHasStableTSC = false;
// ----------------------------------------------------------------------------
// Global constants
@ -600,6 +621,8 @@ TimeStamp::Startup()
InitThresholds();
InitResolution();
sHasStableTSC = HasStableTSC();
LOG(("TimeStamp: initial skew is %1.2fms", mt2ms_d(sSkew)));
return NS_OK;
@ -614,6 +637,9 @@ TimeStamp::Shutdown()
TimeStamp
TimeStamp::Now()
{
if (sHasStableTSC) {
return TimeStamp(uint64_t(PerformanceCounter()));
}
return TimeStamp(uint64_t(CalibratedPerformanceCounter()));
}