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Windows: use EcoQoS for ThreadPriority::Background #148797

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Merged
merged 6 commits into from
Jul 29, 2025
Merged

Windows: use EcoQoS for ThreadPriority::Background #148797

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5c586bf
Windows: use EcoQoS for ThreadPriority::Background
timblechmann Jul 15, 2025
00e16ce
clang-format
aganea Jul 23, 2025
8130f41
Ensure we load the system kernel32.dll and not another injected lib
aganea Jul 23, 2025
670a81a
Use global functions
aganea Jul 23, 2025
c37d94c
Force wchar_t string; move function to WindowsSupport.h
aganea Jul 27, 2025
1975f77
Merge branch 'main' into feature/EcoQoS
aganea Jul 29, 2025
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29 changes: 29 additions & 0 deletions llvm/lib/Support/Windows/Threading.inc
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Original file line number Diff line number Diff line change
Expand Up @@ -107,6 +107,35 @@ void llvm::get_thread_name(SmallVectorImpl<char> &Name) {
}

SetThreadPriorityResult llvm::set_thread_priority(ThreadPriority Priority) {

// SetThreadInformation is only available on Windows 8 and later. Since we still
// support compilation on Windows 7, we load the function dynamically.
typedef BOOL(WINAPI * SetThreadInformation_t)(
HANDLE hThread, THREAD_INFORMATION_CLASS ThreadInformationClass,
_In_reads_bytes_(ThreadInformationSize) PVOID ThreadInformation,
ULONG ThreadInformationSize);
static const auto pfnSetThreadInformation =
(SetThreadInformation_t)GetProcAddress(
GetModuleHandle(TEXT("kernel32.dll")), "SetThreadInformation");

if (pfnSetThreadInformation) {
auto setThreadInformation = [](ULONG ControlMaskAndStateMask) {
THREAD_POWER_THROTTLING_STATE state{};
state.Version = THREAD_POWER_THROTTLING_CURRENT_VERSION;
state.ControlMask = ControlMaskAndStateMask;
state.StateMask = ControlMaskAndStateMask;
return pfnSetThreadInformation(GetCurrentThread(), ThreadPowerThrottling,
&state, sizeof(state));
};

// Use EcoQoS for ThreadPriority::Background available (running on most
// efficent cores at the most efficient cpu frequency):
// https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-setthreadinformation
// https://learn.microsoft.com/en-us/windows/win32/procthread/quality-of-service
setThreadInformation(Priority == ThreadPriority::Background ? THREAD_POWER_THROTTLING_EXECUTION_SPEED
: 0);
}

// https://docs.microsoft.com/en-us/windows/desktop/api/processthreadsapi/nf-processthreadsapi-setthreadpriority
// Begin background processing mode. The system lowers the resource scheduling
// priorities of the thread so that it can perform background work without
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