Bug#898941: caffe-cpu: Very different results for gpu and cpu calculations due to possibly problematic BLAS dependency

[Sébastien Villemot]

On Sat, May 19, 2018 at 12:15:21PM +0000, Lumin wrote:

> Thank you for this bug report. I'll take a look into it.
> 
> Sébastien, I found no code in caffe that is specific to any BLAS
> implementation. Do you have any idea about the reported result variation
> between netlib blas and openblas? Or do they have different level of
> numerical stability assurance?

I don’t have any specific idea about the cause of the problem. But I wouldn’t
be surprised if the different BLAS implementations had different numerical
stability properties is some corner cases, because they do not implement the
algorithms in the same way.

Best,

> > Package: caffe-cpu
> > Severity: important
> > 
> > Dear Maintainer,
> > 
> > I'm getting very different results in cpu mode compared to gpu mode, when using the libblas3 (version 3.7.0-2) package. 
> > After installing the libopenblas-base package (version 0.2.19-3) the problems disappeared. I don't know whether
> > this is a dependency problem of the package or it is a known problem in libblas3. I was able to uninstall and install
> > libopenblas-base while libblas3 was still being installed, which is a little bit confusing to me.
> > 
> > Note that I reported the bug initially here: https://github.com/twhui/MSG-Net/issues/2
> > 
> > Note also that this bug has been found with a recompiled package with matlab support enabled. I used this howto
> > https://github.com/BVLC/caffe/blob/master/docs/install_apt_debian.md, and changed only the matlab options. However, 
> > I don't think that the behaviour is visible in matlab only, though I didn't try this.
> > 
> > Kind Regards
> > Christoph
> > 
> > -- System Information:
> > Debian Release: 9.4
> >   APT prefers stable
> >   APT policy: (1000, 'stable'), (900, 'stable'), (500, 'stable-updates')
> > Architecture: amd64 (x86_64)
> > Foreign Architectures: i386
> > 
> > Kernel: Linux 4.9.0-6-amd64 (SMP w/8 CPU cores)
> > Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en (charmap=UTF-8)
> > Shell: /bin/sh linked to /bin/dash
> > Init: systemd (via /run/systemd/system)
> > 
> > Versions of packages caffe-cpu depends on:
> > pn  caffe-tools-cpu                  <none>
> > ii  libblas3 [libblas.so.3]          3.7.0-2
> > pn  libcaffe-cpu1                    <none>
> > ii  libopenblas-base [libblas.so.3]  0.2.19-3
> > pn  python3-caffe-cpu                <none>
> > 
> > caffe-cpu recommends no packages.
> > 
> > Versions of packages caffe-cpu suggests:
> > pn  caffe-doc         <none>
> > pn  libcaffe-cpu-dev  <none>
> > 

-- 
⢀⣴⠾⠻⢶⣦⠀  Sébastien Villemot
⣾⠁⢠⠒⠀⣿⡁  Debian Developer
⢿⡄⠘⠷⠚⠋⠀  http://sebastien.villemot.name
⠈⠳⣄⠀⠀⠀⠀  http://www.debian.org
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