[Octave-bug-tracker] [bug #62358] Performance of Matrix Multiplication significantly slower in 7.1.0 compared to 6.1.0

[Arun Giridhar]

Update of bug #62358 (project octave):

                  Status:                    None => Confirmed              

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Follow-up Comment #1:

I get similar trends for both single and double. Roughly 6% slower for newer
versions even using the same OpenBLAS.

Octave 8.0.0 dev:

octave:1> bench_mmult
N = 1000
Method 2: MEAN GFLOPS single: 439.98066
Method 2: MAX GFLOPS single: 444.30221


Octave 7.1.0:

octave:4> bench_mmult
N = 1000
Method 2: MEAN GFLOPS single: 434.11718
Method 2: MAX GFLOPS single: 444.75095


Octave 5.2.0:

octave:3> bench_mmult
N =  1000
Method 2: MEAN GFLOPS single: 464.80058
Method 2: MAX GFLOPS single: 470.33189
octave:4> 


The mtimes function (same as the * operator) in data.cc has been unchanged for
the versions tested above, and only calls binary_assoc_op_defun_body in
data.cc, which too has been unchanged for the three versions and calls
binary_op in ov.cc.

Digging deeper in ov.h and ov.cc, the relevant change to binary_op appears to
be https://hg.savannah.gnu.org/hgweb/octave/rev/70cdf8de553d

changeset:   28631:70cdf8de553d
user:        John W. Eaton <jwe@octave.org>
date:        Thu Jul 30 16:16:04 2020 -0400
summary:     move non-member octave_value operator functions to octave
namespace

That change in July 2020 was after 5.2.0 was released (Jan 2020) but before
6.1.0 (Nov 2020). (See https://wiki.octave.org/Release_History for the version
number over time):

CCing jwe for his input. Is there a way to get the performance back?


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