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[common] remove presumed 'hot path' for QPC of 10MHz on SteadyClock::Now() (#4162)

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while this may be true, it isn't required to have this quick path for this function because:
a) arm64
b) counter/freq and counter%freq is a single idiv
c) 2 muls, 2 div isnt that insanely expensive
d) `static_assert(period::den % TenMHz == 0)`

Signed-off-by: lizzie <lizzie@eden-emu.dev>

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4162
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>
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lizzie 2026-07-07 20:03:27 +02:00 • committed by crueter
parent 9677522e6c
commit 94e9c2bd74
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1 changed files with 4 additions and 16 deletions
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20
src/common/steady_clock.cpp
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@ -1,4 +1,4 @@
// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project // SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
// SPDX-License-Identifier: GPL-3.0-or-later // SPDX-License-Identifier: GPL-3.0-or-later
// SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project // SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
@ -48,22 +48,10 @@ static s64 GetSystemTimeNS() {
SteadyClock::time_point SteadyClock::Now() noexcept { SteadyClock::time_point SteadyClock::Now() noexcept {
#if defined(_WIN32) #if defined(_WIN32)
static const auto freq = WindowsQueryPerformanceFrequency(); static const auto timer_freq = WindowsQueryPerformanceFrequency();
const auto counter = WindowsQueryPerformanceCounter(); const auto counter = WindowsQueryPerformanceCounter();
const auto whole = (counter / timer_freq) * period::den;
// 10 MHz is a very common QPC frequency on modern PCs. const auto part = (counter % timer_freq) * period::den / timer_freq;
// Optimizing for this specific frequency can double the performance of
// this function by avoiding the expensive frequency conversion path.
static constexpr s64 TenMHz = 10'000'000;
if (freq == TenMHz) [[likely]] {
static_assert(period::den % TenMHz == 0);
static constexpr s64 Multiplier = period::den / TenMHz;
return time_point{duration{counter * Multiplier}};
}
const auto whole = (counter / freq) * period::den;
const auto part = (counter % freq) * period::den / freq;
return time_point{duration{whole + part}}; return time_point{duration{whole + part}};
#elif defined(__APPLE__) #elif defined(__APPLE__)
return time_point{duration{clock_gettime_nsec_np(CLOCK_MONOTONIC_RAW)}}; return time_point{duration{clock_gettime_nsec_np(CLOCK_MONOTONIC_RAW)}};