Re: getting processor numbers

Cliff Wickman
2007-04-04T14:53:11Z

On Wed, Apr 04, 2007 at 02:47:32AM -0400, Jakub Jelinek wrote:
> On Tue, Apr 03, 2007 at 07:04:58PM -0700, Paul Jackson wrote:
> > There are really at least four "number of CPUs" answers here, and we
> > should be aware of which we are providing. There are, in order of
> > decreasing size:
> > 1) the size of the kernels cpumask_t (NR_CPUS),
> > 2) the maximum number of CPUs that might ever be hotplugged into a
> > booted system,
> > 3) the current number of CPUs online in that system, and
> > 4) the number of CPUs that the current task is allowed to use.
>
> sysconf(_SC_NPROCESSORS_CONF) should IMHO return (2) (this currently
> scans /proc/cpuinfo on alpha and sparc{,64} for ((ncpus|CPUs) probed|cpus detected)
> and for the rest just returns sysconf(_SC_NPROCESSORS_ONLN)).
> Neither of the sysconf returned values should be affected by affinity.

I'm looking at an ia64 system, and when a cpu is hot-unplugged it is removed
from /proc/cpuinfo. Wouldn't /sys/devices/system/cpu/ be a better
source for 2) ?

--
Cliff Wickman
Silicon Graphics, Inc.
cpw@sgi.com
(651) 683-3824