On 10/11/23 23:12, George Ostrouchov wrote:
I agree that the "R Installation and Administration" guide statement about
FlexiBLAS needs an update. Standard R in CentOS Stream 9, which is now downstream from
Fedora, gives the following result for Matrix products in sessionInfo():
sessionInfo()
R version 4.3.1 (2023-06-16)
Platform: x86_64-redhat-linux-gnu (64-bit)
Running under: CentOS Stream 9
Matrix products: default
BLAS/LAPACK: FlexiBLAS OPENBLAS-OPENMP; LAPACK version 3.9.0
…
So OpenBLAS compiled with OpenMP is the default. FlexiBLAS (via the flexiblas
package) is my favorite way to manage core use in multithreaded BLAS
computations. It is also the default in the EasyBuild foss compiler toolchain
for HPC clusters: https://docs.easybuild.io/common-toolchains/
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.
Best
Tomas
What would be a good way to suggest or construct an update?
Best regards,
George
Date: Wed, 27 Sep 2023 15:14:43 +0200
From: =?UTF-8?Q?I=C3=B1aki_Ucar?= <iu...@fedoraproject.org>
To: "r-devel@r-project.org" <R-devel@r-project.org>
Subject: [Rd] About FlexiBLAS in the R-admin docs
Message-ID:
<calexwq2x9gygnxt6s906bkqhd139cp783btdqc4wmem-uku...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi,
Not sure if this is the right place for this. The "R Installation and
Administration" guide states:
Apparently undocumented: FlexiBLAS on Fedora provides a complete LAPACK, but
not the enhanced routines from ATLAS or OpenBLAS.
I'm not sure what this means. FlexiBLAS does provide 100% of BLAS and
LAPACK, and if the active backend (say, OpenBLAS) implements an
enhanced LAPACK routine, then the call is redirected to the backend.
If the user switches to another backend and that routine is not
available there, then the original LAPACK routine is dispatched
instead.
Best,
--
Iñaki Úcar
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