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Profiler: Implement QPCClock to get better precision on Win32
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.
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2 changed files with 42 additions and 1 deletions
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@ -6,6 +6,12 @@
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#include "common/profiler_reporting.h"
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#include "common/assert.h"
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#if defined(_MSC_VER) && _MSC_VER <= 1800 // MSVC 2013.
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#define NOMINMAX
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#define WIN32_LEAN_AND_MEAN
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#include <Windows.h> // For QueryPerformanceCounter/Frequency
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#endif
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namespace Common {
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namespace Profiling {
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@ -13,6 +19,23 @@ namespace Profiling {
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thread_local Timer* Timer::current_timer = nullptr;
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#endif
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#if defined(_MSC_VER) && _MSC_VER <= 1800 // MSVC 2013
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QPCClock::time_point QPCClock::now() {
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static LARGE_INTEGER freq;
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// Use this dummy local static to ensure this gets initialized once.
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static BOOL dummy = QueryPerformanceFrequency(&freq);
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LARGE_INTEGER ticks;
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QueryPerformanceCounter(&ticks);
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// This is prone to overflow when multiplying, which is why I'm using micro instead of nano. The
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// correct way to approach this would be to just return ticks as a time_point and then subtract
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// and do this conversion when creating a duration from two time_points, however, as far as I
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// could tell the C++ requirements for these types are incompatible with this approach.
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return time_point(duration(ticks.QuadPart * std::micro::den / freq.QuadPart));
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}
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#endif
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TimingCategory::TimingCategory(const char* name, TimingCategory* parent)
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: accumulated_duration(0) {
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@ -18,8 +18,26 @@ namespace Profiling {
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#define ENABLE_PROFILING 1
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#endif
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using Duration = std::chrono::nanoseconds;
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#if defined(_MSC_VER) && _MSC_VER <= 1800 // MSVC 2013
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// MSVC up to 2013 doesn't use QueryPerformanceCounter for high_resolution_clock, so it has bad
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// precision. We manually implement a clock based on QPC to get good results.
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struct QPCClock {
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using duration = std::chrono::microseconds;
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using time_point = std::chrono::time_point<QPCClock>;
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using rep = duration::rep;
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using period = duration::period;
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static const bool is_steady = false;
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static time_point now();
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};
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using Clock = QPCClock;
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#else
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using Clock = std::chrono::high_resolution_clock;
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#endif
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using Duration = Clock::duration;
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/**
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* Represents a timing category that measured time can be accounted towards. Should be declared as a
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