Skip to content

add specialization for 24MHz QueryPerformanceFrequency #3832

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
Stephan T. Lavavej (StephanTLavavej) merged 9 commits into from
Jul 14, 2023
Merged

add specialization for 24MHz QueryPerformanceFrequency #3832

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
9 commits
Select commit Hold shift + click to select a range
f7479ab
add specialization for 24MHz QueryPerformanceFrequency
fsb4000 Jun 25, 2023
2877870
remove likely and unlikely
fsb4000 Jun 25, 2023
b4557d4
restore likely/unlikely logic
fsb4000 Jun 25, 2023
9b32bef
code review suggestions
fsb4000 Jun 28, 2023
5b995f0
remove _STL_ prefix
fsb4000 Jun 28, 2023
0829dfa
typo
fsb4000 Jun 28, 2023
d4e3b49
refactor
fsb4000 Jun 28, 2023
92d37c7
Code review feedback.
StephanTLavavej Jul 6, 2023
d9d5de1
Restore emulation comment.
StephanTLavavej Jul 7, 2023
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
32 changes: 27 additions & 5 deletions stl/inc/__msvc_chrono.hpp
View file
Open in desktop

@strega-nil-ms nicole mazzuca (strega-nil-ms) Jul 7, 2023

Copy link
Copy Markdown
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Do we need to do the push_macro/undef/pop_macro magic incantation here for likely and unlikely?

@StephanTLavavej Stephan T. Lavavej (StephanTLavavej) Jul 7, 2023

Copy link
Copy Markdown
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

likely and unlikely are commonly defined as function-like macros, but not object-like macros. <xkeycheck.h> avoids rejecting them for that reason.

Unlike msvc etc., users are technically not supposed to macroize likely and unlikely, so we technically don't need to defend against them. We could but I don't think it's necessary at the moment.

Original file line number Diff line number Diff line change
Expand Up @@ -666,18 +666,37 @@ namespace chrono {
using time_point = _CHRONO time_point<steady_clock>;
static constexpr bool is_steady = true;

#if defined(_M_ARM) || defined(_M_ARM64) // vvv ARM or ARM64 arch vvv
#define _LIKELY_ARM_ARM64 _LIKELY
#define _LIKELY_X86_X64
#elif defined(_M_IX86) || defined(_M_X64) // ^^^ ARM or ARM64 arch / x86 or x64 arch vvv
#define _LIKELY_ARM_ARM64
#define _LIKELY_X86_X64 _LIKELY
#else // ^^^ x86 or x64 arch / other arch vvv
#define _LIKELY_ARM_ARM64
#define _LIKELY_X86_X64
#endif // ^^^ other arch ^^^
_NODISCARD static time_point now() noexcept { // get current time
const long long _Freq = _Query_perf_frequency(); // doesn't change after system boot
const long long _Ctr = _Query_perf_counter();
static_assert(period::num == 1, "This assumes period::num == 1.");
// 10 MHz is a very common QPC frequency on modern PCs. Optimizing for
// this specific frequency can double the performance of this function by
// avoiding the expensive frequency conversion path.
constexpr long long _TenMHz = 10'000'000;
if (_Freq == _TenMHz) {
// The compiler recognizes the constants for frequency and time period and uses shifts and
Comment thread
StephanTLavavej marked this conversation as resolved.
// multiplies instead of divides to calculate the nanosecond value.
constexpr long long _TenMHz = 10'000'000;
constexpr long long _TwentyFourMHz = 24'000'000;
// clang-format off
if (_Freq == _TenMHz) _LIKELY_X86_X64 {
// 10 MHz is a very common QPC frequency on modern x86/x64 PCs. Optimizing for
// this specific frequency can double the performance of this function by
// avoiding the expensive frequency conversion path.
static_assert(period::den % _TenMHz == 0, "It should never fail.");
constexpr long long _Multiplier = period::den / _TenMHz;
return time_point(duration(_Ctr * _Multiplier));
} else if (_Freq == _TwentyFourMHz) _LIKELY_ARM_ARM64 {
// 24 MHz is a common frequency on ARM/ARM64, including cases where it emulates x86/x64.
const long long _Whole = (_Ctr / _TwentyFourMHz) * period::den;
const long long _Part = (_Ctr % _TwentyFourMHz) * period::den / _TwentyFourMHz;
return time_point(duration(_Whole + _Part));
} else {
// Instead of just having "(_Ctr * period::den) / _Freq",
// the algorithm below prevents overflow when _Ctr is sufficiently large.
Expand All @@ -688,7 +707,10 @@ namespace chrono {
const long long _Part = (_Ctr % _Freq) * period::den / _Freq;
return time_point(duration(_Whole + _Part));
}
// clang-format on
}
#undef _LIKELY_ARM_ARM64
#undef _LIKELY_X86_X64
};

_EXPORT_STD using high_resolution_clock = steady_clock;
Expand Down
14 changes: 14 additions & 0 deletions stl/inc/yvals_core.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -525,6 +525,20 @@
#define _FALLTHROUGH
#endif

#ifndef __has_cpp_attribute // vvv no attributes vvv
#define _LIKELY
#define _UNLIKELY
#elif __has_cpp_attribute(likely) >= 201803L && __has_cpp_attribute(unlikely) >= 201803L // ^^^ no attr / C++20 attr vvv
#define _LIKELY [[likely]]
#define _UNLIKELY [[unlikely]]
#elif defined(__clang__) // ^^^ C++20 attributes / clang attributes and C++17 or C++14 vvv
#define _LIKELY [[__likely__]]
#define _UNLIKELY [[__unlikely__]]
#else // ^^^ clang attributes and C++17 or C++14 / C1XX attributes and C++17 or C++14 vvv
#define _LIKELY
#define _UNLIKELY
#endif // ^^^ C1XX attributes and C++17 or C++14 ^^^

// _HAS_NODISCARD (in vcruntime.h) controls:
// [[nodiscard]] attributes on STL functions

Expand Down