Re: [PATCH] support for accessing CPU/core count (processor-count)

[Omar Polo]

Campbell Barton <ideasman42@gmail.com> writes:

> Hi, this patch adds support for accessing the number of CPU's / cores
> on a system, matching CPython's multiprocessing.cpu_count() [0].
>
> I've only tested this for Linux, this includes code that should work
> on other platforms, although that would need to be double-checked of
> course.
> For reference I checked CPython / Blender & Stack-overflow [1]

I can confirm it works on OpenBSD too, but needs tweaking.  Some
comments inline and attaching an updated patch

> Accessing this information can be useful to automatically detect the
> number of jobs to run.
>
>
> [0]:
> https://docs.python.org/3/library/multiprocessing.html#multiprocessing.cpu_count
> [1]: https://stackoverflow.com/a/3006416/432509
>
> commit 7be53f10f3df3c3183cc97d6bbadb78ebb61e8d2
> Author: Campbell Barton <ideasman42@gmail.com>
> Date:   Sun Oct 10 10:16:47 2021 +1100
> 
>     Support accessing the number of CPU's.
> 
>     Add (processor-count) for accessing the number of cores/CPU's.
> 
> diff --git a/src/emacs.c b/src/emacs.c
> index 866e43fda9..26e2f6b1f2 100644
> --- a/src/emacs.c
> +++ b/src/emacs.c
> @@ -3156,6 +3156,38 @@ DEFUN ("daemon-initialized", Fdaemon_initialized, 
> Sdaemon_initialized, 0, 0, 0,
>    return Qt;
>  }
> 
> +DEFUN ("processor-count", Fprocessor_count, Sprocessor_count, 0, 0, 0,
> +       doc: /* Return the number of CPUs in the system.
> +
> +The value will always be above zero, 1 for unsupported systems.  */)
> +  (void)
> +{
> +  int nproc = -1;
> +#ifdef WINDOWSNT
> +  SYSTEM_INFO info;
> +  GetSystemInfo(&info);
> +  nproc = (int)info.dwNumberOfProcessors;
> +#elif defined (__APPLE__) || \
> +      defined (__OpenBSD__) || \
> +      defined (__FreeBSD__) || \
> +      defined (__NetBSD__) || \
> +      defined (__DragonFly__)
> +  int mib[2];
> +  size_t len;
> +
> +  mib[0] = CTL_HW;

the #include <sys/sysctl.h> is missing.

> +  mib[1] = HW_NCPU;

at least on OpenBSD this should be HW_NCPUONLINE.

OpenBSD disables hyperthreading by default so HW_NCPU is (almost) always
misleading.  For example, on my machine

        % uname -a
        OpenBSD venera 7.0 GENERIC.MP#221 amd64
        % sysctl hw.ncpu
        hw.ncpu=8
        % sysctl hw.ncpuonline
        hw.ncpuonline=4

and this has been the case for a while already (I mean, a couple of
years if not more.)

I don't have access to other BSDs other than OpenBSD, but judging from
the manpages online.

 - NetBSD has hw.ncpuonline
 - DragonFly and FreeBSD have only hw.ncpu
 - apple I don't know how to check.  man.apple.com doesn't seem to
   exists ^^"

> +  len = sizeof(nproc);
> +  sysctl(mib, 2, &nproc, &len, nullptr, 0);
                                  ^^^^^^^
shouldn't this be NULL?

> +#elif defined (__hpux)
> +  nproc = mpctl(MPC_GETNUMSPUS, NULL, NULL);
> +#elif defined (_SC_NPROCESSORS_ONLN)
> +  nproc = (int)sysconf(_SC_NPROCESSORS_ONLN);
> +#endif
> +
> +  return make_fixnum (MAX(nproc, 1));

emacs.c:3188:23: warning: implicit declaration of function 'MAX' is invalid in 
C99 [-Wimplicit-function-declaration]

I'm attaching an updated patch.  Note that I'm not sure if including
sys/types.h and sys/sysctl.h breaks the build on some OS.

if someone knows how to reduce the number of #ifdefs I'll be glad :)

> +}
> +

Cheers,

Omar Polo

>From 5fe26a73abc60eae7dd2528e3854f2f379bcb4c7 Mon Sep 17 00:00:00 2001
From: Campbell Barton <ideasman42@gmail.com>
Date: Sun, 10 Oct 2021 08:21:01 +0000
Subject: [PATCH] add function to access the number of CPU

* emacs.c (Fprocessor_count): add processor-count function to access
  the number of CPU
---
 src/emacs.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/src/emacs.c b/src/emacs.c
index 866e43fda9..5bd10a7586 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -25,6 +25,8 @@ along with GNU Emacs.  If not, see 
<https://www.gnu.org/licenses/>.  */
 #include <fcntl.h>
 #include <stdlib.h>
 
+#include <sys/types.h>
+#include <sys/sysctl.h>
 #include <sys/file.h>
 #include <sys/stat.h>
 #include <unistd.h>
@@ -3156,6 +3158,38 @@ from the parent process and its tty file descriptors.  
*/)
   return Qt;
 }
 
+DEFUN ("processor-count", Fprocessor_count, Sprocessor_count, 0, 0, 0,
+       doc: /* Return the number of CPUs in the system.
+
+The value will always be above zero, 1 for unsupported systems.  */)
+  (void)
+{
+  int nproc = -1;
+#ifdef WINDOWSNT
+  SYSTEM_INFO info;
+  GetSystemInfo(&info);
+  nproc = (int)info.dwNumberOfProcessors;
+#elif defined (HW_NCPU) || defined (HW_NCPUONLINE)
+  int mib[2];
+  size_t len;
+
+  mib[0] = CTL_HW;
+#ifdef HW_NCPUONLINE
+  mib[1] = HW_NCPUONLINE;
+#else
+  mib[1] = HW_NCPU;
+#endif
+  len = sizeof(nproc);
+  sysctl(mib, 2, &nproc, &len, NULL, 0);
+#elif defined (__hpux)
+  nproc = mpctl(MPC_GETNUMSPUS, NULL, NULL);
+#elif defined (_SC_NPROCESSORS_ONLN)
+  nproc = (int)sysconf(_SC_NPROCESSORS_ONLN);
+#endif
+
+  return make_fixnum (nproc > 1 ? nproc : 1);
+}
+
 void
 syms_of_emacs (void)
 {
@@ -3176,6 +3210,7 @@ syms_of_emacs (void)
   defsubr (&Sinvocation_directory);
   defsubr (&Sdaemonp);
   defsubr (&Sdaemon_initialized);
+  defsubr (&Sprocessor_count);
 
   DEFVAR_LISP ("command-line-args", Vcommand_line_args,
               doc: /* Args passed by shell to Emacs, as a list of strings.
-- 
2.33.0