From 5ce2b45bb3498767402f16cb4975399da9527690 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Matthias=20A=C3=9Fhauer?= Date: Sat, 21 Feb 2026 12:11:02 +0100 Subject: [PATCH] win32: thread-utils: handle multi-socket systems MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit While the currently used way to detect the number of CPU cores on Windows is nice and straight-forward, GetSystemInfo() only gives us access to the number of processors within the current group. [1] While that is usually fine for systems with a single physical CPU, separate physical sockets are typically separate groups. Switch to using GetLogicalProcessorInformationEx() to handle multi-socket systems better. [1] https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/ns-sysinfoapi-system_info#members This fixes https://github.com/git-for-windows/git/issues/4766 Co-Authored-by: Herman Semenov Signed-off-by: Matthias Aßhauer --- thread-utils.c | 27 ++++++++++++++++++++++----- 1 file changed, 22 insertions(+), 5 deletions(-) diff --git a/thread-utils.c b/thread-utils.c index 374890e6b0..00e7e9192b 100644 --- a/thread-utils.c +++ b/thread-utils.c @@ -28,11 +28,28 @@ int online_cpus(void) #endif #ifdef GIT_WINDOWS_NATIVE - SYSTEM_INFO info; - GetSystemInfo(&info); - - if ((int)info.dwNumberOfProcessors > 0) - return (int)info.dwNumberOfProcessors; + DWORD len = 0; + if (!GetLogicalProcessorInformationEx(RelationProcessorCore, NULL, &len) && GetLastError() == ERROR_INSUFFICIENT_BUFFER) { + uint8_t *buf = malloc(len); + if (buf) { + if (GetLogicalProcessorInformationEx(RelationProcessorCore, (PSYSTEM_LOGICAL_PROCESSOR_INFORMATION_EX) buf, &len)) { + DWORD offset = 0; + int n_cores = 0; + while (offset < len) { + PSYSTEM_LOGICAL_PROCESSOR_INFORMATION_EX info = (PSYSTEM_LOGICAL_PROCESSOR_INFORMATION_EX) (buf + offset); + offset += info->Size; + /* The threads within a core always share a single group. We need to count the bits in the mask to get a thread count. */ + for (KAFFINITY mask = info->Processor.GroupMask[0].Mask; mask; mask >>= 1) + n_cores += mask &1; + } + if (n_cores) { + free(buf); + return n_cores; + } + } + free(buf); + } + } #elif defined(hpux) || defined(__hpux) || defined(_hpux) struct pst_dynamic psd;