Re: [PATCH] core-count: A new program to count the number of cpucores

[Gilles Espinasse]

----- Original Message ----- 
From: "Giuseppe Scrivano" <address@hidden>
To: "Bruno Haible" <address@hidden>
Cc: <address@hidden>; <address@hidden>; "Jim Meyering"
<address@hidden>
Sent: Monday, October 26, 2009 12:45 AM
Subject: Re: [PATCH] core-count: A new program to count the number of
cpucores


...
> > 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].
>
> Probably it is better to add an option, making a difference between the
> number of "real" and "effective" cores.  Where it is not possible to
> know correctly the latter, they'll coincide.
>
>
> >   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]
>
> What about leave to the user the decisione to use less threads/processes
> than core-count reports?
>
> For example, assuming that `sort' will soon get the --threads option and
> an user decides to use all cores except one to sort a file, then it can
> be done as:
>
> sort --threads="$(($(core-count) - 1))" huge_file
>
>
> Cheers,
> Giuseppe
>
>
that assume --threads is able to handle negative count or 0
Would not be more efficient to handle the count in core-count?
That mean core-count should always report a minimum of 1 and discount from
total the number passed as an option.

Probably the first usage of core-count will be to feed make -j

Gilles