[llvm-dev] Benchmark LNT weird thread behaviour

Chris Matthews via llvm-dev llvm-dev at lists.llvm.org
Tue Sep 20 17:33:03 PDT 2016

I think every job should define those or use the LNT default of 1,1.  The validity of compile time and exec time metrics is in question if the job is loaded incorrectly, so it makes sense to me to not allow that -j to get passed through.

On September 20, 2016 at 4:30:04 AM, Renato Golin via llvm-dev (llvm-dev at lists.llvm.org) wrote:

On 20 September 2016 at 01:17, Chris Matthews <chris.matthews at apple.com> wrote:
> There seems to be three interesting flags in your LNT invocations:
> -j2 --threads=1 --build-threads=4
> Since -j and --threads are the same flag, I think that is the problem. The
> first -j flag is at the start of the LNT command, perhaps that is coming
> from a different part of zorg?

-j2 is from "jobs=2" in the builder's argument list, to compile Clang.
This also gets passed to LNT, since nt_flags is not required, and you
do want to use all cores if nothing is specified.

Of course, when --threads is specified, you have the conflict, but
since this argument is not required, I wouldn't want to omit the -j2
from LNT at all.

I could "fix" this in our builder to not pass -jN into LNT and always
use nt_flags, but I don't think that is a good fix, since other users
will have odd behaviour on their side. Unless that's the kind of
behaviour we *want* to encode, of course.

What do you think?

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