Re: forcing local build from a package definition

[Federico Beffa <beffa@ieee.org>]

On Fri, Oct 24, 2014 at 8:57 PM, Eric Bavier <ericbavier@gmail.com> wrote:
> ATLAS frequently pulls its tuning configuration information from a table
> of known values at configuration time.  I think there is also a way to
> tell it which architecture it should be built for.

Let me try to better explain the problem: ATLAS needs to know the
exact type of CPU on which it is running for best performance. This is
because it tries to make best use of all available features:
Say, you have a recent CPU with 8 cores and instructions set including
SSE1 SSE2 SSE3.  If you specify this type of CPU, ATLAS will build a
library with procedures which make use of 8 parallel threads and try
to exploit all available instructions at best. However, the library
will not run on an older CPU, say, with no SSE3. And perform poorly on
a two cores CPU.

To avoid this type of problem you may specify the simplest type of CPU
that you want to support at configure time (and this is the approach
of most distributions which are only delivering binary). However, if
you then install the "low" spec generic library on your brand new CPU
with 8 cores it will perform poorly.

If we force the library to be built on the machine on which it will be
used, then everyone will get the most out of the library.  That is the
reason for asking if there is a way to force a local build from within
a package definition.

Hope this better explains the reason for my question.
Regards,
Fede