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Retrieve the number of online CPUs on OpenBSD and NetBSD #1916

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Retrieve the number of online CPUs on OpenBSD and NetBSD #1916

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14 changes: 10 additions & 4 deletions src/sysinfo.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -153,11 +153,11 @@ ValueUnion GetSysctlImp(std::string const& name) {
int mib[2];

mib[0] = CTL_HW;
if ((name == "hw.ncpu") || (name == "hw.cpuspeed")) {
if ((name == "hw.ncpuonline") || (name == "hw.cpuspeed")) {
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not ncpufound?

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The sysctl name is hw.ncpuonline.

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https://man.openbsd.org/sysctl.2 includes ncpufound which seems to be more predictable in some cases (from brief reading i did). i'm not an expert but i want to make sure that we're picking the right one.

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@brad0 brad0 Feb 6, 2025 •
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ncpufound is the same as ncpu. On OpenBSD X86 systems have SMT disabled by default so the number of CPUs would be double what is actually online and available. This is functionally equivalent to what is used on other OS's with sysconf(_SC_NPROCESSORS_ONLN) instead of _SC_NPROCESSORS_CONF.

ValueUnion buff(sizeof(int));

if (name == "hw.ncpu") {
mib[1] = HW_NCPU;
if (name == "hw.ncpuonline") {
mib[1] = HW_NCPUONLINE;
} else {
mib[1] = HW_CPUSPEED;
}
Expand Down Expand Up @@ -482,7 +482,13 @@ std::string GetSystemName() {
int GetNumCPUsImpl() {
#ifdef BENCHMARK_HAS_SYSCTL
int num_cpu = -1;
if (GetSysctl("hw.ncpu", &num_cpu)) return num_cpu;
constexpr auto* hwncpu =
#ifdef HW_NCPUONLINE
"hw.ncpuonline";
#else
"hw.ncpu";
#endif
if (GetSysctl(hwncpu, &num_cpu)) return num_cpu;
PrintErrorAndDie("Err: ", strerror(errno));
#elif defined(BENCHMARK_OS_WINDOWS)
SYSTEM_INFO sysinfo;
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