Hi Nikita, > From: Nikita Ermakov <a...@altlinux.org> > > - Update comments to correspond closed glibc bug #21542. > > - In case of failed _SC_NPROCESSORS_CONF use the maximum between > nprocs_current and nprocs to meet the requirements of > num_processors (NPROC_ALL) >= num_processors (NPROC_CURRENT).
Thanks for the report. To summarize, sysconf (_SC_NPROCESSORS_CONF) may now return 2 instead of 1, in situations where the number of processors cannot be determined because /proc and /sys are not mounted. The rationale given in <https://sourceware.org/bugzilla/show_bug.cgi?id=21542> is that there are "applications which use the return value to recognize uniprocessor systems and apply optimizations based on that". > diff --git a/lib/nproc.c b/lib/nproc.c > index 77b876027..a550711b4 100644 > --- a/lib/nproc.c > +++ b/lib/nproc.c > @@ -217,17 +217,14 @@ num_processors_ignoring_omp (enum nproc_query query) > the /sys and /proc file systems (see > glibc/sysdeps/unix/sysv/linux/getsysstats.c). > In some situations these file systems are not mounted, and the sysconf > - call returns 1, which does not reflect the reality. */ > + call returns 1 or 2, which does not reflect the reality. */ > + unsigned long nprocs_current = num_processors_via_affinity_mask (); > > if (query == NPROC_CURRENT) > { > /* Try the modern affinity mask system call. */ > - { > - unsigned long nprocs = num_processors_via_affinity_mask (); > - > - if (nprocs > 0) > - return nprocs; > - } > + if (nprocs_current > 0) > + return nprocs_current; > > #if defined _SC_NPROCESSORS_ONLN > { /* This works on glibc, Mac OS X 10.5, FreeBSD, AIX, OSF/1, Solaris, > @@ -249,15 +246,10 @@ num_processors_ignoring_omp (enum nproc_query query) > /* On Linux systems with glibc, this information comes from the /sys > and > /proc file systems (see > glibc/sysdeps/unix/sysv/linux/getsysstats.c). > In some situations these file systems are not mounted, and the > - sysconf call returns 1. But we wish to guarantee that > + sysconf call returns 1 or 2. But we wish to guarantee that > num_processors (NPROC_ALL) >= num_processors (NPROC_CURRENT). */ > - if (nprocs == 1) > - { > - unsigned long nprocs_current = num_processors_via_affinity_mask > (); > - > - if (nprocs_current > 0) > - nprocs = nprocs_current; > - } > + if (nprocs_current > nprocs) > + nprocs = nprocs_current; > # endif > > if (nprocs > 0) Your patch goes in the right direction. But it causes additional, unnecessary calls to num_processors_via_affinity_mask () in two situations: - on systems other than glibc/Linux systems, - on glibc/Linux systems on which sysconf (_SC_NPROCESSORS_CONF) returned a value > 2. I'm therefore applying this slightly different patch: 2019-06-10 Bruno Haible <br...@clisp.org> nproc: Ensure nproc(NPROC_ALL) ≥ nproc(NPROC_CURRENT) with glibc ≥ 2.26. Reported by Nikita Ermakov <a...@altlinux.org> in <https://lists.gnu.org/archive/html/bug-gnulib/2019-06/msg00003.html>. * lib/nproc.c (num_processors_ignoring_omp): Treat a return value of sysconf (_SC_NPROCESSORS_CONF) == 2 like a return value == 1. diff --git a/lib/nproc.c b/lib/nproc.c index 77b8760..b11690b 100644 --- a/lib/nproc.c +++ b/lib/nproc.c @@ -216,8 +216,9 @@ num_processors_ignoring_omp (enum nproc_query query) Note! On Linux systems with glibc, the first and second number come from the /sys and /proc file systems (see glibc/sysdeps/unix/sysv/linux/getsysstats.c). - In some situations these file systems are not mounted, and the sysconf - call returns 1, which does not reflect the reality. */ + In some situations these file systems are not mounted, and the sysconf call + returns 1 or 2 (<https://sourceware.org/bugzilla/show_bug.cgi?id=21542>), + which does not reflect the reality. */ if (query == NPROC_CURRENT) { @@ -249,13 +250,13 @@ num_processors_ignoring_omp (enum nproc_query query) /* On Linux systems with glibc, this information comes from the /sys and /proc file systems (see glibc/sysdeps/unix/sysv/linux/getsysstats.c). In some situations these file systems are not mounted, and the - sysconf call returns 1. But we wish to guarantee that + sysconf call returns 1 or 2. But we wish to guarantee that num_processors (NPROC_ALL) >= num_processors (NPROC_CURRENT). */ - if (nprocs == 1) + if (nprocs == 1 || nprocs == 2) { unsigned long nprocs_current = num_processors_via_affinity_mask (); - if (nprocs_current > 0) + if (/* nprocs_current > 0 && */ nprocs_current > nprocs) nprocs = nprocs_current; } # endif
