# [PATCH] thread-utils.c: detect online CPU count on OpenBSD / NetBSD 4 messages from 2025-05-09 to 2025-06-01. Participants: Brad Smith, Patrick Steinhardt, Collin Funk. Thread: https://gitlist.dev/t/63426 ## Brad Smith, 2025-05-09 06:13 Subject: [PATCH] thread-utils.c: detect online CPU count on OpenBSD / NetBSD Message-ID: URL: https://gitlist.dev/e/aB2c-W0V83aVDpZr%40humpty.home.comstyle.com ``` 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 --- 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; -- 2.49.0 ``` ## Patrick Steinhardt, 2025-05-09 08:36 Subject: Re: [PATCH] thread-utils.c: detect online CPU count on OpenBSD / NetBSD Message-ID: URL: https://gitlist.dev/e/aB2-lwKPOnj3EH0b%40pks.im In-Reply-To: ``` On Fri, May 09, 2025 at 02:13:13AM -0400, Brad Smith wrote: > 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 > --- > 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 ``` ## Brad Smith, 2025-05-31 20:18 Subject: Re: [PATCH] thread-utils.c: detect online CPU count on OpenBSD / NetBSD Message-ID: URL: https://gitlist.dev/e/f929a4b5-1011-42dd-ad86-bb654d170db2%40comstyle.com In-Reply-To: ``` ping. On 2025-05-09 2:13 a.m., Brad Smith wrote: > 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 > --- > 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; ``` ## Collin Funk, 2025-06-01 02:14 Subject: Re: [PATCH] thread-utils.c: detect online CPU count on OpenBSD / NetBSD Message-ID: <87msas5ht5.fsf@gmail.com> URL: https://gitlist.dev/e/87msas5ht5.fsf%40gmail.com In-Reply-To: ``` Hi Brad, You wrote: > 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 > --- > thread-utils.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) Looks good to me. I tested the patch on OpenBSD 7.7 and NetBSD 10.0. Reviewed-by: Collin Funk Collin ```