Re: luaffi/luaffi question: Calling c function ptr possible?

[Javier Guerra Giraldez <javier@...>]

On Fri, Jul 10, 2015 at 12:07 PM, Tom N Harris <whoopdedo@whoopdedo.org> wrote:
> FFI isn't just an extra dependency for you to carry, it's also very, very slow
> unless you're using LuaJIT.


a very rough speed ranking of Lua->C interfacing methods, from fastest
to slowest:

1.- LuaJIT, fully compiled FFI
2.- LuaJIT, Lua C API
3.- PUC Lua, Lua C API
4.- LuaJIT, intepreted FFI
5.- any Lua, luaffi module

notes:

- even better than 1: don't use C.  it's faster to do tight loops in
fully compiled Lua code than to call C code for small things.

- big (several orders of magnitude) difference from 1 to 2

- 2 and 3 are roughly similar.  an interesting data point is the Redis
server. It can use LuaJIT, but there's very small performance
advantage (the author cites around 10%)

- very perceptible difference from 3 to 4 (that's why under LuaJIT you
shouldn't use the FFI in tight loops if you're not sure this inner
code is compiled)

- i haven't personally benchmarked the luaffi module (case 5), but
it's a pretty heavy wrapping on top of the Lua C API, so it's
noticeably slower than 3.  the 4 case does much of the same, but in
the core of the LuaJIT interpreter (which is quite fast, in fact)
instead of the C API, so it has a significant advantage over 5.  my
feeling is that the difference from 4 to 5 is similar to the one from
3 to 4.

-- 
Javier