Re: [PATCH] thread-utils.c: detect online CPU count on OpenBSD / NetBSD
From: Patrick Steinhardt <hidden>
Date: 2025-05-09 08:36:46
On Fri, May 09, 2025 at 02:13:13AM -0400, Brad Smith wrote:
quoted hunk ↗ jump to hunk
OpenBSD / NetBSD use HW_NCPUONLINE to detect the online CPU count. OpenBSD ships with SMT disabled on X86 systems so HW_NCPU would provide double the number of CPUs as opposed to the proper online count. Signed-off-by: Brad Smith <redacted> --- thread-utils.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)diff --git a/thread-utils.c b/thread-utils.c index 1f89ffab4c..374890e6b0 100644 --- a/thread-utils.c +++ b/thread-utils.c@@ -46,11 +46,11 @@ int online_cpus(void) mib[0] = CTL_HW; # ifdef HW_AVAILCPU mib[1] = HW_AVAILCPU; - len = sizeof(cpucount); - if (!sysctl(mib, 2, &cpucount, &len, NULL, 0)) - return cpucount; -# endif /* HW_AVAILCPU */ +# elif defined(HW_NCPUONLINE) + mib[1] = HW_NCPUONLINE; +# else mib[1] = HW_NCPU; +# endif /* HW_AVAILCPU */ len = sizeof(cpucount); if (!sysctl(mib, 2, &cpucount, &len, NULL, 0)) return cpucount;
This change looks sensible to me and matches the documentation at [1]. Using the number of online CPUs instead of existing CPUs certainly matches the expectation of what this function should reutrn. Thanks! Patrick [1]: https://man.openbsd.org/sysctl.2#HW_NCPUONLINE~2