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authorcheloha <cheloha@cvs.openbsd.org>2018-07-12 01:23:39 +0000
committercheloha <cheloha@cvs.openbsd.org>2018-07-12 01:23:39 +0000
commit002672cb62f0ac2d4943a71f9ffdf5e1ec38e10d (patch)
tree1f01707e432a7f62f55ac7c1fa4880b4b059b9b5 /lib/libcxx
parent83a7dd06f8186000336c23fb99f58ba067be43b8 (diff)
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/libcxx')
-rw-r--r--lib/libcxx/src/thread.cpp4
1 files changed, 2 insertions, 2 deletions
diff --git a/lib/libcxx/src/thread.cpp b/lib/libcxx/src/thread.cpp
index 467402b6b42..d4977cd9a73 100644
--- a/lib/libcxx/src/thread.cpp
+++ b/lib/libcxx/src/thread.cpp
@@ -78,9 +78,9 @@ thread::detach()
unsigned
thread::hardware_concurrency() _NOEXCEPT
{
-#if defined(CTL_HW) && defined(HW_NCPU)
+#if defined(CTL_HW) && defined(HW_NCPUONLINE)
unsigned n;
- int mib[2] = {CTL_HW, HW_NCPU};
+ int mib[2] = {CTL_HW, HW_NCPUONLINE};
std::size_t s = sizeof(n);
sysctl(mib, 2, &n, &s, 0, 0);
return n;