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From: "quanhua.liu at noaa dot gov" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug fortran/106565] Using a transposed matrix in matmul
 (GCC-10.3.0) is very slow
Date: Tue, 09 Aug 2022 17:17:57 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106565

--- Comment #5 from Quanhua Liu <quanhua.liu at noaa dot gov> ---
Hi Richard,

Using -fexternal-blas for gfortran v10.3.0 is much slower than
the method 2:
 =C2=A0 BB =3D transpose(B)
 =C2=A0 C =3D matmul(A, BB)

How about on your machine?

Thanks,

Quanhua Liu
On 8/9/2022 11:07 AM, kargl at gcc dot gnu.org wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106565
>
> kargl at gcc dot gnu.org changed:
>
>             What    |Removed                     |Added
> -------------------------------------------------------------------------=
---
>                   CC|                            |kargl at gcc dot gnu.org
>
> --- Comment #3 from kargl at gcc dot gnu.org ---
>
>>        INTEGER, PARAMETER :: m =3D 200, n =3D 300, nn =3D 150
>>        REAL :: A(m,n), B(nn,n), C(m,nn), BB(n,nn)
>>        INTEGER :: i, j, k, L
>
> If you are doing a problem of this size or larger, you want to use the
> -fexternal-blas option and link in OpenBLAS.
>
> I added timing code and replicated the loop to both in one go.
>
> % gfcx -o z -O3 -march=3Dnative a.f90 && ./z
>     1.16500998       1615.08594
>     5.32258606       1615.08020
> % gfcx -o z -O3 -march=3Dnative a.f90 -fexternal-blas -lopenblas && ./z
>     2.44668889       1615.08301
>     1.99379802       1615.08301
>=