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| author |   cheloha <cheloha@openbsd.org> | 2018-07-12 01:23:38 +0000 |
|---|---|---|
| committer | cheloha <cheloha@openbsd.org> | 2018-07-12 01:23:38 +0000 |
| commit | c71ddef4e977e565d25356bbc54b3876cbf432d2 (patch) | |
| tree | b490dcb814f23972da3ddb68d992362aa1c16ddf /lib/libc/gen/sysconf.c | |
| parent | Explicitly call "/etc/rc.d/vmd stop". This issues graceful shutdown commands (diff) | |
| download | wireguard-openbsd-c71ddef4e977e565d25356bbc54b3876cbf432d2.tar.xz wireguard-openbsd-c71ddef4e977e565d25356bbc54b3876cbf432d2.zip | |
Add hw.ncpuonline to count the number of online CPUs.
The introduction of hw.smt means that logical CPUs can be disabled
after boot and prior to suspend/resume. If hw.smt=0 (the default),
there needs to be a way to count the number of hardware threads
available on the system at any given time.
So, import HW_NCPUONLINE/hw.ncpuonline from NetBSD and document it.
hw.ncpu becomes equal to the number of CPUs given to sched_init_cpu()
during boot, while hw.ncpuonline is equal to the number of CPUs available
to the scheduler in the cpuset "sched_all_cpus". Set_SC_NPROCESSORS_ONLN
equal to this new sysctl and keep _SC_NPROCESSORS_CONF equal to hw.ncpu.
This is preferable to adding a new sysctl to count the number of
configured CPUs and keeping hw.ncpu equal to the number of online
CPUs because such a change would break software in the ecosystem
that relies on HW_NCPU/hw.ncpu to measure CPU usage and the like.
Such software in base includes top(1), systat(1), and snmpd(8),
and perhaps others.
We don't need additional locking to count the cardinality of a cpuset
in this case because the only interfaces that can modify said cardinality
are sysctl(2) and ioctl(2), both of which are under the KERNEL_LOCK.
Software using HW_NCPU/hw.ncpu to determine optimal parallism will need
to be updated to use HW_NCPUONLINE/hw.ncpuonline. Until then, such software
may perform suboptimally. However, most changes will be similar to the
change included here for libcxx's std::thread:hardware_concurrency():
using HW_NCPUONLINE in lieu of HW_NCPU should be sufficient for determining
optimal parallelism for most software if the change to _SC_NPROCESSORS_ONLN
is insufficient.
Prompted by deraadt. Discussed at length with kettenis, deraadt, and sthen.
Lots of patch tweaks from kettenis.
ok kettenis, "proceed" deraadt
Diffstat (limited to 'lib/libc/gen/sysconf.c')
| -rw-r--r-- | lib/libc/gen/sysconf.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/lib/libc/gen/sysconf.c b/lib/libc/gen/sysconf.c index e73bc437dab..1bcc2a7bc90 100644 --- a/lib/libc/gen/sysconf.c +++ b/lib/libc/gen/sysconf.c @@ -1,4 +1,4 @@ -/* $OpenBSD: sysconf.c,v 1.25 2017/09/10 18:20:00 guenther Exp $ */ +/* $OpenBSD: sysconf.c,v 1.26 2018/07/12 01:23:38 cheloha Exp $ */ /*- * Copyright (c) 1993 * The Regents of the University of California. All rights reserved. @@ -461,7 +461,7 @@ sysconf(int name) break; case _SC_NPROCESSORS_ONLN: mib[0] = CTL_HW; - mib[1] = HW_NCPU; + mib[1] = HW_NCPUONLINE; break; default: |