On 5/7/24 20:44, Toon Moene wrote:
On 5/7/24 20:35, Andrew Pinski wrote:
On Tue, May 7, 2024 at 11:31 AM Toon Moene <t...@moene.org> wrote:
On 5/7/24 00:02, Toon Moene wrote:
OK, perhaps on the aarch64 I need the following option to make the
comparison fair:
‘rdma’
Enable Round Double Multiply Accumulate instructions. This is
on by
default for -march=armv8.1-a.
I.e., -mno-rdma
(I hope that's correct - I'll will try that when the Sun rises again
and
I have some power to run the AArch64 machine ...).
Well, I did two independent runs with gfortran-13.2 and the following
options:
-O3 -march=armv8.1-a+rdma
and
-O3 -march=armv8.1-a+nordma
No difference in the number of error runs exceeding the prescribed
thresholds.
So, unless I made a mistake in the option specification (or the compiler
silently ignored them because they were not applicable to my machine -
ugh), the cause of the problem lies elsewhere.
AARCH64 armv8-a has FMA as part of its base ISA.
So you want to try with `-ffp-contract=off` instead.
RDMA turns on/off instructions which are not used by the
auto-vectorizer (yet) and used by intrinsics for them (If I read the
code correctly).
Ah, thanks - I'll try that tomorrow.
Yep, that did it:
--> LAPACK TESTING SUMMARY <--
Processing LAPACK Testing output found in the TESTING directory
SUMMARY nb test run numerical error other error
================ =========== ================= ================
REAL 1327023 0 (0.000%) 0
(0.000%)
DOUBLE PRECISION 1327845 0 (0.000%) 0
(0.000%)
COMPLEX 786775 0 (0.000%) 0
(0.000%)
COMPLEX16 787842 0 (0.000%) 0
(0.000%)
--> ALL PRECISIONS 4229485 0 (0.000%) 0 (0.000%)
So, obviously, the threshold values for these tests were derived on a
machine without fused-multiply-add, or without using them if present.
This is perhaps not surprising, as the default build-and-test setup
(make.inc.example) of the LAPACK package as distributed from netlib.org
lists as the compiler choice:
FC = gfortran
FFLAGS = -O2 -frecursive
FFLAGS_DRV = $(FFLAGS)
FFLAGS_NOOPT = -O0 -frecursive
which means that the choice of architecture on x86-64 would be "generic"
and wouldn't include FMA instructions. If the authors had used that
setup in deriving the thresholds, it is not surprising that you need
-ffp-contract=off on architectures that include FMA instructions by default.
Thanks for helping me out with this !
--
Toon Moene - e-mail: t...@moene.org - phone: +31 346 214290
Saturnushof 14, 3738 XG Maartensdijk, The Netherlands
