Build doesn't fail when no backends cannot be built

[scaljeri]

I tried to run lc0 inside a docker container. I followed the instructions for Ubuntu 18.04.

$> CC=clang-6.0 CXX=clang++-6.0 INSTALL_PREFIX=~/.local ./build.sh

Downloaded a weight file from here Now when I try to run

$> ./lc0 -w LD2.pb.gz
       _
|   _ | |
|_ |_ |_| v0.22.0-dev built Jun 23 2019
go
Loading weights file from: /LD2.pb.gz
Creating backend [check]... 
Working backend set to opencl.
Reference backend set to blas.
Creating backend [opencl]...
error Unknown backend: opencl

I cannot find much about backend, but I noticed that when I use a backend which doesn't exist it will list the available backends:

 ./lc0 -w /LD2.pb.gz -b xyz
         _
 |   _ | |
 |_ |_ |_| v0.22.0-dev built Jun 23 2019
 terminate called after throwing an instance of 'lczero::Exception'
  what():  Flag '--backend' must be one of the following values: check random roundrobin 
 multiplexing demux.
 Aborted

So, I've tried all of them and only random seems to work, but I would like it to play a good game against, for example, stockfish. Now. I'm using an old mac book (2013) so I guess I can only use some kinds of CPU backend

Is this possible and is this somewhere documented (Lc0 inside docker and backends)

Found an article that states:

And BLAS is for running Lc0 not with a GPU, but with a CPU. That is MUCH slower

But how can I define a BLAS backend? Or is there a better alternative for my docker on my macbook?

[mooskagh]

It wasn't able to build any sensible (not random-playing) backend, probably because required libraries were not installed in the system. What's broken though (other than "check" backend having higher priority than "random", I've just sent #900 for that) is that it was built successfully, it was supposed to fail the build explaining what's going on.

[scaljeri]

Ok, so thats the reason, thnx. I just installed Blas and it works like a charm :)

[borg323]

The BLAS backend should be buildable with Eigen out of the box (and mey be faster than openblas since it is customized for the build machine). Try adding -Dblas=true -Deigen=true at the end of the build command.

[DanielUranga]

If you have a GPU that supports CUDA the best approach would be to use this Docker image: danieluranga/leela_chess_zero-lc0_ubuntu_builder and Nvidia Docker.

[scaljeri]

Thanks a lot, this is all I needed. If all is working find, CUDA will be the next step!

[mooskagh]

I've re-purposed this issue to build-should-fail one. (originally introduced in this commit: https://github.com/LeelaChessZero/lc0/commit/d9f1652744998954a20d341da495902cd7046645, not sure when stopped working).

[borg323]

This is very weird. Reviewing meson.build everything seems like it should be, and trying to build on a fresh windows 10 VM (with no cuda/opencl/blas) the build did indeed fail. @scaljeri do you still have the log from the lc0 build reported in the first post?

Edit: The only scenario I can come up with, it that there was an earlier build with -Dbuild_backends=false. The options from previous builds are cached and should be explicitly reversed.

[scaljeri]

I don't have the old images/containers anymore and I cannot reproduce it :( It just works now as expected. Super weird.

[Naphthalin]

@mooskagh if I understand you correctly, the issue described here should now fail successfully?

[borg323]

We never figured out what the problem was, the build does fails correctly for me (I did test it a few days ago coincidentally) but it should have failed back then as well.