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Windows: use EcoQoS for ThreadPriority::Background#148797
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llvmbot commentedJul 15, 2025 • edited
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@llvm/pr-subscribers-platform-windows @llvm/pr-subscribers-llvm-support Author: Tim Blechmann (timblechmann) ChangesThe SetThreadInformation API allows threads to be scheduled on the most efficient cores on the most efficient frequency. Full diff:https://github.com/llvm/llvm-project/pull/148797.diff 1 Files Affected:
diff --git a/llvm/lib/Support/Windows/Threading.inc b/llvm/lib/Support/Windows/Threading.incindex d862dbd7f71c9..b52c6dff4e5f4 100644--- a/llvm/lib/Support/Windows/Threading.inc+++ b/llvm/lib/Support/Windows/Threading.inc@@ -107,6 +107,31 @@ void llvm::get_thread_name(SmallVectorImpl<char> &Name) { } SetThreadPriorityResult llvm::set_thread_priority(ThreadPriority Priority) {++ 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) {+ if (Priority == ThreadPriority::Background) {+ // 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+ THREAD_POWER_THROTTLING_STATE state;+ memset(&state, 0, sizeof(state));+ state.Version = THREAD_POWER_THROTTLING_CURRENT_VERSION;+ state.ControlMask = THREAD_POWER_THROTTLING_EXECUTION_SPEED;+ state.StateMask = THREAD_POWER_THROTTLING_EXECUTION_SPEED;+ pfnSetThreadInformation(GetCurrentThread(), ThreadPowerThrottling, &state,+ sizeof(state));+ }+ }+ // 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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The SetThreadInformation API allows threads to be scheduled on the mostefficient cores on the most efficient frequency.Using this API for ThreadPriority::Background should make clangd-basedIDEs a little less CPU hungry.
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Thanks for the changes. Just some more minor nits:
| @@ -107,6 +107,39 @@ void llvm::get_thread_name(SmallVectorImpl<char> &Name) { | |||
| } | |||
| SetThreadPriorityResultllvm::set_thread_priority(ThreadPriority Priority) { | |||
| // SetThreadInformation is only available on Windows 8 and later. so we load | |||
| // it at run-time | |||
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Can you please mention explicitely that we want to keep compatibility with Windows 7?
| // 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 | ||
| if (Priority == ThreadPriority::Background) { | ||
| setThreadInformation(THREAD_POWER_THROTTLING_EXECUTION_SPEED, |
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For the current requirements, we don't need to be that verbose here, just one value would suffice here (and use it for both control mask and state mask above).
The SetThreadInformation API allows threads to be scheduled on the most efficient cores on the most efficient frequency.
Using this API for ThreadPriority::Background should make clangd-based IDEs a little less CPU hungry.