On 9/3/24 15:07, Jan Hubicka wrote:
Hi,
We disable gathers for zen4. It seems that gather has improved a bit compared
to zen4 and Zen5 optimization manual suggests "Avoid GATHER instructions when
the indices are known ahead of time. Vector loads followed by shuffles result
in a higher load bandwidth." however the situation seems to be more
complicated.
A small bit of "real world" experience (but for zen3):
Recently I switched to gfortran 14.2 for my weather forecasting.
A year ago I had changed "-march=native -mtune=native" (on my zen3
system) to "-march=native -mtune=znver2" while using gfortran 13 - it
had only a small effect (but positive).
Last Monday I switched back to "-march=native -mtune=native", but that
consistently made a 12 hour computation around 6 minutes slower (i.e.,
about 1/120th, or 0.8 %). The most computational intensive part of the
code needs gather (either instructions or inline expansions of them).
Hope this helps,
--
Toon Moene - e-mail: t...@moene.org - phone: +31 346 214290
Saturnushof 14, 3738 XG Maartensdijk, The Netherlands
