GNU bug report logs - #51536
openblas builds not reproducible on different x86_64 machines

Previous Next

Full log

View this message in rfc822 format

From: Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
To: Efraim Flashner <efraim <at> flashner.co.il>
Cc: 51536 <at> debbugs.gnu.org
Subject: bug#51536: openblas builds not reproducible on different x86_64 machines
Date: Fri, 05 Nov 2021 12:38:00 -0400

Hi Efraim!

Efraim Flashner <efraim <at> flashner.co.il> writes:

[...]

> I compared our build flags with Debian's¹ (which is also what I often do
> when working on other architectures) and it looks like they have
> DYNAMIC_OLDER=1 and TARGET=GENERIC. From looking through Makefile.system
> it looks like TARGET=GENERIC makes it more portable, and DYNAMIC_OLDER=1
> adds support for some of the older x86_64 sub-architectures.

DYNAMIC_OLDER is probably a good idea (it'll inflate the binary size a
bit), but I doubt it's the culprit here, as my problematic CPU is a
Q6700 from the CORE2 family, already supposed to be covered by
DYNAMIC_ARCH=1 on x86 (c.f. Makefile.system):

--8<---------------cut here---------------start------------->8---
ifeq ($(DYNAMIC_ARCH), 1)
ifeq ($(ARCH), x86)
DYNAMIC_CORE = KATMAI COPPERMINE NORTHWOOD PRESCOTT BANIAS \
	       CORE2 PENRYN DUNNINGTON NEHALEM ATHLON OPTERON OPTERON_SSE3 BARCELONA BOBCAT ATOM NANO
endif
--8<---------------cut here---------------end--------------->8---

From that same Makefile, TARGET=GENERIC seems to only do:

--8<---------------cut here---------------start------------->8---
ifdef TARGET
GETARCH_FLAGS := -DFORCE_$(TARGET)
GETARCH_FLAGS += -DUSER_TARGET
ifeq ($(TARGET), GENERIC)
ifeq ($(DYNAMIC_ARCH), 1)
override NO_EXPRECISION=1
export NO_EXPRECiSION
endif
endif
endif
--8<---------------cut here---------------end--------------->8---

I.e. it sets NO_EXPRECISION to 1 and exports it (with a typo!).  Perhaps
good to fix that typo and try it!

> If it weren't for the 2k+ packages which depend on openblas I think it'd
> be obvious to add the extra flags now. I wonder if we could
> unconditionally set DYNAMIC_ARCH=1 TARGET=GENERIC and then override it
> on some architectures, rather than now where each architecture needs its
> own flags.

I've rebuilt core-updates-frozen-batched-changes so many times now I'm
not too afraid of it anymore ;-).

> I also wonder if it's worth it to add a minimal openblas-native for an
> easy transform option of --with-graft=openblas=openblas-native, where
> openblas-native just adds -march=native and turns off substitutability.

Seems this could be done easily by someone already rewriting their Guix
packages graph.

To be continued...

Maxim

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.