On 11/1/23 13:29, Iñaki Ucar wrote:
On Wed, 1 Nov 2023 at 12:57, Tomas Kalibera <tomas.kalib...@gmail.com> wrote:
On 10/31/23 10:45, Iñaki Ucar wrote:
On Tue, 24 Oct 2023 at 12:53, Tomas Kalibera <tomas.kalib...@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.
This depends on how you configure R. On Fedora 38,
../trunk/configure --with-blas=flexiblas --with-lapack
reports "BLAS(FlexiBlas), LAPACK(in blas)" and from my reading of
R-admin, this is the recommended way of configuring with flexiblas.
Configuring via (is this what you had in mind?):
../trunk/configure --with-blas=flexiblas --with-lapack=flexiblas
reports "BLAS(FlexiBlas), LAPACK(generic)". The build would actually do
"-lflexiblas -lflexiblas", the former for LAPACK (from --with-lapack
value) and the latter for BLAS (from --with-blas value). The "generic"
here means not from BLAS, but from an extra standalone library. Compare
with the first (recommended) use when the build would only link
"-lflexiblas" once.
I see. I didn't understand that part then. I thought that a library
should be specified.
I read this from R-Admin re --with-lapack:
"In practice its main uses are without a value,
- with an `enhanced' BLAS such as ATLAS, FlexiBLAS, MKL or OpenBLAS which
contains a full LAPACK (to avoid possible conflicts), or
- on Debian/Ubuntu systems to select the system liblapack which can
be switched by the `alternatives' mechanism.
"
I've updated configure in R-devel to detect when the same library is
specified explicitly for blas and lapack, so that now even that is
handled and reported as LAPACK in Blas libs.
Best
Tomas
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
