[erlang-questions] erlc speed (or lack thereof), Make and emake

[Dmitry Kolesnikov]

Hello,

I had a following construction in Makefiles

%.beam : %.erl
        $(AM_V_ERL)$(ERLC) $(ERL_CFLAGS) -I ./include -b beam \$<

define rules_ERLAPP
$(1)_BEAM=$(subst .in,,$(addprefix ebin/, $(notdir $($(1)_SRC:.erl=.beam))))
nobase_pkgliberl_SCRIPTS += $$($(1)_BEAM)
...
endef

It build only touched file… there was no issue with slow compile. 
But I've swapped to rebar just to stream line my workflow and still no issues :-)

- Dmitry

On Jan 25, 2013, at 12:04 AM, Matthias Lang <matthias@REDACTED> wrote:

> On Thursday, January 24, Tim Watson wrote:
> 
>> Take a look at the Rabbit Makefile - it doesn't recompile all the
>> time *and* it works with -J and is generally really fast.
> 
> That Makefile is nice and tidy, but it's compiling the .erl files in
> the simplest---and slowest---way possible. It calls 'erlc' about 370
> times, i.e. once per file. I.e. exactly as per "Bad Idea #1" in my OP.
> 
> Quick measurements on building 3.0.1 from source:
> 
>  plain 'make': 220s wall time
>   'make -j 2': 112s
> 
> I wanted to get an idea of how much of a speedup was possible, so I
> broke out all the calls to 'erlc' from the build process and put
> them in a shell script. There are about 370.
> 
> Running the script so it does one call to 'erlc' at a time takes 183s.
> 
> Changing the script so that each call to 'erlc' compiles many files
> drops the time to 40s.
> 
> Further changing the script to use multiple (unix) processes gets me to 26s.
> 
> That's pretty encouraging. It suggests that a 3x or 4x speedup is
> possible for the Erlang part of the Rabbit build process.
> 
> Matt
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