[erlang-bugs] Erlang 18.0-rc1 is behaving slower than 17.4 (and 17.5)

[Michael Truog]

On 04/07/2015 03:44 PM, José Valim wrote:
> I have first noticed this issue when compiling Elixir's grammar. Compiling yrl -> erl -> beam is about 20% slower in Erlang 18.0-rc1. The results are shown below:
>
> https://gist.github.com/josevalim/ab08341512ba875fb4a7
>
> To further verify the performance issues, I have decided to run Elixir's test suite with 18.0 and 17.4. Elixir test suite defines a lot of modules dynamically when loading so that would be a good test. The results are here:
>
> https://gist.github.com/josevalim/895e2365d5ae517b1c8a
>
> It is interesting that the load/compile times are indeed higher in 18.0 but the test suite is also taking *longer*. This may imply it is not the compiler that is slower but Erlang itself. I have run the test suite of other projects in different Erlang versions (same Elixir version though) and seen similar slow down. About a 20% slow down on Erlang 18.0-rc1 overall.
>
> Unfortunately, I don't have any idea why this is happening. I have asked others to compile the same .yrl file and they have seen similar performance hit. It is easy to reproduce it. Download the elixir_parser.yrl file:
>
> https://github.com/elixir-lang/elixir/blob/v1.0/lib/elixir/src/elixir_parser.yrl
>
> And run both commands:
>
>     $ time erlc +time elixir_parser.yrl
>     $ time erlc +time elixir_parser.erl
>
> I hope by posting this report others can be alert to similar issues in their projects.
>
> Thoughts?
>
> *José Valim*
> www.plataformatec.com.br <http://www.plataformatec.com.br/>
> Skype: jv.ptec
> Founder and Lead Developer
>
>
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I have used rebar2 (using the tag "2.1.0-pre") to compile CloudI with 18.0-rc1 and have had a few builds go extremely slow, to the point I needed to kill the build and restart it (slow only during the rebar2 usage).  This problem appears to be transient and I haven't been able to reproduce it consistently, but I assume it is related to how escript is running.  I have other escripts that use "-mode(compile)." which don't have this problem.

I haven't done enough runtime usage of 18.0-rc1 to really determine that this is or isn't related to the Erlang compilation, but it makes more sense to me that it is a transient slowness with the Erlang VM itself, for reasons unknown.
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