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Detect number of cores better on multi-socket systems (#6108)

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While the currently used way to detect the number of CPU cores ond
Windows is nice and straight-forward, GetSystemInfo() only [gives us
access to the number of processors within the current
group.](https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/ns-sysinfoapi-system_info#members)

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.

I've tested this on a physical single-socket x86-64 and a physical
dual-socket x86-64 system, and on a virtual single-socket ARM64 system.
Physical [multi-socket ARM64 systems seem to
exist](https://cloudbase.it/ampere-altra-industry-leading-arm64-server/),
but I don't have access to such hardware and the hypervisor I use
apparently can't emulate that either.
This commit is contained in:
Johannes Schindelin
2026-04-06 12:25:16 +02:00
committed by GitHub
parent d14b57281c 5ce2b45bb3
commit 7c2288da5c
1 changed files with 22 additions and 5 deletions
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27
thread-utils.c
View File

@@ -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;