Re: [PATCH] core-count: A new program to count the number of cpu cores (original) (raw)

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From: Bruno Haible
Subject: Re: [PATCH] core-count: A new program to count the number of cpu cores
Date: Sun, 25 Oct 2009 22:41:00 +0100
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Giuseppe Scrivano wrote:

I went for `core-count'. This is the first version of the new program, it is a simple wrapper around the gnulib nproc module

This program (and the underlying gnulib 'nproc' module) is IMO too simplistic.

First of all, is the program meant to be a hardware inspection tool (like "hwinfo --cpu")? Or is meant to be an auxiliary program for helping shell scripts that want to dispatch tasks onto a maximum number of processors?

If it is meant to be a hardware inspection tool, then it should IMO try to reflect current multiprocessing hardware architectures. I mean the fact that a computer's central unit can have several thread execution units, combined at three different levels:

If it is meant as a tool for helping the parallelization of tasks at the shell script level, then it needs to take into account

  1. the fact that the current process may be limited to a certain subset of the available CPUs. See the Linux/NetBSD function pthread_setaffinity_np [5][6] and the IRIX notion of a CPU that is available only to root processes [7].
  2. the wish of users to not use all processors at once. Users may want to save 1 CPU for their GUI interactions. This can most comfortably be done through an environment variable, such as OMP_NUM_THREADS. [8] An implementation that considers 1) and 2) can be found in OpenMP. So, why not simply use the function omp_set_num_threads() that is provided by GCC in its libgomp library (in a compiler agnostic way through the AC_OPENMP macro of Autoconf)?

Bruno

[1] http://en.wikipedia.org/wiki/Multiprocessing [2] http://en.wikipedia.org/wiki/Multi-chip_module [3] http://en.wikipedia.org/wiki/Multi-core_(computing) [4] http://en.wikipedia.org/wiki/Hyper-threading [5] http://www.kernel.org/doc/man-pages/online/pages/man3/pthread_setaffinity_np.3.html [6] http://www.daemon-systems.org/man/pthread_getaffinity_np.3.html [7] http://techpubs.sgi.com/library/tpl/cgi-bin/getdoc.cgi?cmd=getdoc&coll=0650&db=man&fname=2%20sysmp [8] http://gcc.gnu.org/onlinedocs/libgomp/OMP_005fNUM_005fTHREADS.html