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Merge pull request #10935 from Morph1984/mwaitx

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x64: Make use of monitorx instructions for power efficient sleeps (AMD)
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liamwhite 2023-06-29 10:01:26 -04:00 committed by GitHub
commit 5e70db0d43
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4 changed files with 41 additions and 14 deletions
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1
src/common/telemetry.cpp
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@ -93,6 +93,7 @@ void AppendCPUInfo(FieldCollection& fc) {
add_field("CPU_Extension_x64_GFNI", caps.gfni);
add_field("CPU_Extension_x64_INVARIANT_TSC", caps.invariant_tsc);
add_field("CPU_Extension_x64_LZCNT", caps.lzcnt);
add_field("CPU_Extension_x64_MONITORX", caps.monitorx);
add_field("CPU_Extension_x64_MOVBE", caps.movbe);
add_field("CPU_Extension_x64_PCLMULQDQ", caps.pclmulqdq);
add_field("CPU_Extension_x64_POPCNT", caps.popcnt);

1
src/common/x64/cpu_detect.cpp
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@ -168,6 +168,7 @@ static CPUCaps Detect() {
__cpuid(cpu_id, 0x80000001);
caps.lzcnt = Common::Bit<5>(cpu_id[2]);
caps.fma4 = Common::Bit<16>(cpu_id[2]);
caps.monitorx = Common::Bit<29>(cpu_id[2]);
}
if (max_ex_fn >= 0x80000007) {

1
src/common/x64/cpu_detect.h
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@ -63,6 +63,7 @@ struct CPUCaps {
bool gfni : 1;
bool invariant_tsc : 1;
bool lzcnt : 1;
bool monitorx : 1;
bool movbe : 1;
bool pclmulqdq : 1;
bool popcnt : 1;

52
src/common/x64/cpu_wait.cpp
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@ -13,36 +13,60 @@
namespace Common::X64 {
namespace {
// 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
constexpr auto PauseCycles = 100'000U;
} // Anonymous namespace
#ifdef _MSC_VER
__forceinline static void TPAUSE() {
// 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
static constexpr auto PauseCycles = 100'000;
_tpause(0, FencedRDTSC() + PauseCycles);
static constexpr auto RequestC02State = 0U;
_tpause(RequestC02State, FencedRDTSC() + PauseCycles);
}
__forceinline static void MWAITX() {
static constexpr auto EnableWaitTimeFlag = 1U << 1;
static constexpr auto RequestC1State = 0U;
// monitor_var should be aligned to a cache line.
alignas(64) u64 monitor_var{};
_mm_monitorx(&monitor_var, 0, 0);
_mm_mwaitx(EnableWaitTimeFlag, RequestC1State, PauseCycles);
}
#else
static void TPAUSE() {
// 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
static constexpr auto PauseCycles = 100'000;
static constexpr auto RequestC02State = 0U;
const auto tsc = FencedRDTSC() + PauseCycles;
const auto eax = static_cast<u32>(tsc & 0xFFFFFFFF);
const auto edx = static_cast<u32>(tsc >> 32);
asm volatile("tpause %0" : : "r"(0), "d"(edx), "a"(eax));
asm volatile("tpause %0" : : "r"(RequestC02State), "d"(edx), "a"(eax));
}
static void MWAITX() {
static constexpr auto EnableWaitTimeFlag = 1U << 1;
static constexpr auto RequestC1State = 0U;
// monitor_var should be aligned to a cache line.
alignas(64) u64 monitor_var{};
asm volatile("monitorx" : : "a"(&monitor_var), "c"(0), "d"(0));
asm volatile("mwaitx" : : "a"(RequestC1State), "b"(PauseCycles), "c"(EnableWaitTimeFlag));
}
#endif
void MicroSleep() {
static const bool has_waitpkg = GetCPUCaps().waitpkg;
static const bool has_monitorx = GetCPUCaps().monitorx;
if (has_waitpkg) {
TPAUSE();
} else if (has_monitorx) {
MWAITX();
} else {
std::this_thread::yield();
}