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proper calcs for nanoseconds

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This commit is contained in:
lizzie 2026-05-23 09:50:29 +00:00
parent c9c858a614
commit d04b9da170
5 changed files with 43 additions and 44 deletions
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41
src/common/x64/cpu_wait.cpp
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@ -21,29 +21,24 @@ __attribute__((target("waitpkg,mwaitx")))
#pragma GCC target("waitpkg")
#pragma GCC target("mwaitx")
#endif
void MicroSleep(u64 rem) {
// 100,000 cycles is a reasonable amount of time to wait to save on CPU resources.
// For reference:
// At 1 GHz, 100K cycles is 100us
// At 2 GHz, 100K cycles is 50us
// At 4 GHz, 100K cycles is 25us
auto& caps = GetCPUCaps();
u32 cycles = caps.invariant_tsc
? rem * (caps.tsc_frequency / 1000000ULL)
: 1'000'000ULL;
if (caps.waitpkg) {
constexpr auto RequestC02State = 0U;
_tpause(RequestC02State, FencedRDTSC() + cycles);
} else if (caps.monitorx) {
constexpr auto EnableWaitTimeFlag = 1U << 1;
constexpr auto RequestC1State = 0U;
// monitor_var should be aligned to a cache line.
alignas(64) static const u64 monitor_var{};
_mm_monitorx(const_cast<u64*>(std::addressof(monitor_var)), 0, 0);
_mm_mwaitx(EnableWaitTimeFlag, RequestC1State, cycles);
} else {
std::this_thread::yield();
}
void MicroSleep(const CPUCaps& caps, u64 cycles) {
do {
u64 start = FencedRDTSC();
if (caps.waitpkg) {
constexpr auto RequestC02State = 0U;
_tpause(RequestC02State, start + cycles);
} else if (caps.monitorx) {
constexpr auto EnableWaitTimeFlag = 1U << 1;
constexpr auto RequestC1State = 0U;
// monitor_var should be aligned to a cache line.
alignas(64) static const u64 monitor_var{};
_mm_monitorx(const_cast<u64*>(std::addressof(monitor_var)), 0, 0);
_mm_mwaitx(EnableWaitTimeFlag, RequestC1State, cycles);
} else {
std::this_thread::yield();
}
cycles -= FencedRDTSC() - start;
} while (cycles > 0);
}
} // namespace Common::X64

3
src/common/x64/cpu_wait.h
View file

@ -4,9 +4,10 @@
#pragma once
#include "common/common_types.h"
#include "common/x64/cpu_detect.h"
namespace Common::X64 {
void MicroSleep(u64 rem);
void MicroSleep(const CPUCaps& caps, u64 cycles);
} // namespace Common::X64