From: Steve Kargl <sgk@troutmask.apl.washington.edu>
To: Thomas Koenig <tkoenig@netcologne.de>
Cc: Richard Biener <richard.guenther@gmail.com>,
Tobias Burnus <tobias@codesourcery.com>,
"fortran@gcc.gnu.org" <fortran@gcc.gnu.org>
Subject: Re: MATMUL broken with frontend optimization.
Date: Thu, 18 Mar 2021 13:22:39 -0700 [thread overview]
Message-ID: <20210318202239.GA25584@troutmask.apl.washington.edu> (raw)
In-Reply-To: <f549cd59-0e4f-bf3e-91f8-26c12816ce63@netcologne.de>
On Thu, Mar 18, 2021 at 07:24:21PM +0100, Thomas Koenig wrote:
> I didn't finish the previous mail before hitting "send", so here
> is the postscript...
>
> > OK, so I've had a bit of time to look at the actual test case. I
> > missed one very important detail before: This is a vector-matrix
> > operation.
> >
> > For this, we do not have a good library routine (Harald just
> > removed it because of a bug in buffering), and -fexternal-blas
> > does not work because we do not handle calls to anything but
> > *GEMM.
>
> A vector-matrix multiplicatin would be a call to *GEMV, a worthy
> goal, but out of scope so close to a release.
Agreed.
> > The idea is that, for a vector-matrix-multiplication, the
> > compiler should have enough information about the information
> about how to optimize for the relevant architecture, especially
> if the user compilers with the right flags.
>
> So, the current idea is that, if we optimize, we can inline.
>
> What would a better heuristic be?
>
Does _gfortran_matmul_r4 (and friends) work for vector-matrix
products? I haven't checked. If so, how about disabling
in-lining MATMUL for 11.1; then, for 11.2, this can be revisited
where a small N can be chosen for in-lining. With -fexternal-blas
and *gemm, the default cross-over is N = 30.
BTW, I cam across this in StackOverflow.
https://stackoverflow.com/questions/66682180/why-is-matmul-slower-with-gfortran-compiler-optimization-turned-on
--
Steve
next prev parent reply other threads:[~2021-03-18 20:22 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-18 7:48 Steve Kargl
2021-03-18 12:35 ` Richard Biener
2021-03-18 14:48 ` Tobias Burnus
2021-03-18 15:05 ` Richard Biener
2021-03-18 16:13 ` Steve Kargl
2021-03-18 18:16 ` Thomas Koenig
2021-03-18 18:24 ` Thomas Koenig
2021-03-18 20:22 ` Steve Kargl [this message]
2021-03-18 20:55 ` Thomas Koenig
2021-03-18 22:07 ` Steve Kargl
2021-03-19 6:19 ` Thomas Koenig
2021-03-19 6:36 ` Thomas Koenig
2021-03-19 19:12 ` Steve Kargl
2021-03-19 7:03 ` Steve Kargl
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