[Rd] About FlexiBLAS in the R-admin docs

[Iñaki Ucar]

On Tue, 24 Oct 2023 at 12:53, Tomas Kalibera <tomas.kalibera using gmail.com> wrote:
>
> The output of session info is based on that flexiblas is used and on
> what flexiblas tells R is the backend it uses. R does not attempt to
> check that optimized LAPACK functions from the backend really end up
> called via flexiblas, and I don't think it could be realistically checked.
>
> But I've checked one case manually in Fedora 38 using Linux perf tool.
> The following code:
>
> S <- toeplitz((10:1)/10)
> repeat { R <- rWishart(10, 20, S) }
>
> uses dpotrf from LAPACK, which is optimized in OpenBLAS and ATLAS and
> the corresponding optimized implementations really appeared on the
> sampling profile for me from the backend libraries.
>
> The comment from R Admin has been removed now and if anyone runs into
> the problem (that an optimized LAPACK function is not called from a
> backend that provides it), it would be best to report it with sufficient
> detail to flexiblas.

Thanks, Tomas. Yes, if an expected redirection to an optimized
function does not happen, that would be a bug in FlexiBLAS and should
be reported upstream.

Related to this, a small detail... I noticed that the R configure
script reports "BLAS(FlexiBlas)" correctly as an external library, but
then "LAPACK(generic)". This should be FlexiBLAS too instead of
"generic". It doesn't make any difference, since the LAPACK symbols in
FlexiBLAS are called anyway, but it's misleading.

Best,
-- 
Iñaki Úcar