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Profiler: Implement QPCClock to get better precision on Win32

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MSVC 2013 (at least) doesn't use QueryPerformanceCounter to implement
std::chrono::high_resolution_clock, so it has bad precision. Manually
implementing our own clock type using it works around this for now.
This commit is contained in:
Yuri Kunde Schlesner 2015-02-15 15:49:27 -02:00
parent cd1fbfcf1b
commit dc8a3f8bc8
2 changed files with 42 additions and 1 deletions
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23
src/common/profiler.cpp
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@ -6,6 +6,12 @@
#include "common/profiler_reporting.h"
#include "common/assert.h"
#if defined(_MSC_VER) && _MSC_VER <= 1800 // MSVC 2013.
#define NOMINMAX
#define WIN32_LEAN_AND_MEAN
#include <Windows.h> // For QueryPerformanceCounter/Frequency
#endif
namespace Common {
namespace Profiling {
@ -13,6 +19,23 @@ namespace Profiling {
thread_local Timer* Timer::current_timer = nullptr;
#endif
#if defined(_MSC_VER) && _MSC_VER <= 1800 // MSVC 2013
QPCClock::time_point QPCClock::now() {
static LARGE_INTEGER freq;
// Use this dummy local static to ensure this gets initialized once.
static BOOL dummy = QueryPerformanceFrequency(&freq);
LARGE_INTEGER ticks;
QueryPerformanceCounter(&ticks);
// This is prone to overflow when multiplying, which is why I'm using micro instead of nano. The
// correct way to approach this would be to just return ticks as a time_point and then subtract
// and do this conversion when creating a duration from two time_points, however, as far as I
// could tell the C++ requirements for these types are incompatible with this approach.
return time_point(duration(ticks.QuadPart * std::micro::den / freq.QuadPart));
}
#endif
TimingCategory::TimingCategory(const char* name, TimingCategory* parent)
: accumulated_duration(0) {

20
src/common/profiler.h
View file

@ -18,8 +18,26 @@ namespace Profiling {
#define ENABLE_PROFILING 1
#endif
using Duration = std::chrono::nanoseconds;
#if defined(_MSC_VER) && _MSC_VER <= 1800 // MSVC 2013
// MSVC up to 2013 doesn't use QueryPerformanceCounter for high_resolution_clock, so it has bad
// precision. We manually implement a clock based on QPC to get good results.
struct QPCClock {
using duration = std::chrono::microseconds;
using time_point = std::chrono::time_point<QPCClock>;
using rep = duration::rep;
using period = duration::period;
static const bool is_steady = false;
static time_point now();
};
using Clock = QPCClock;
#else
using Clock = std::chrono::high_resolution_clock;
#endif
using Duration = Clock::duration;
/**
* Represents a timing category that measured time can be accounted towards. Should be declared as a