[erlang-questions] zlib driver in erlang seems very slow

[Sergej Jurečko]

If you care about compression speed zlib is a terrible choice anyway. Also in your NIF you seem to be doing the entire compression on a scheduler thread all in one go. This is very bad. NIF calls should not take more than ~1ms.

Sergej

> On 09 Mar 2016, at 11:54, Caragea Silviu <silviu.cpp@REDACTED> wrote:
> 
> Hello guys,
> 
> While investigating some benchmarks with zlib on erlang I suspected that the elrang driver might be too slow. 
> Initially I wrote a small c++ app linking with zlib doing almost the same stuff like my erlang testing script and I found a big gap in performance between them.
> Initial thought was that the difference might come from the overhead added by erlang itself. (converting from elrang terms into c++ data and vice versa)
> 
> Then I started creating my own nif library for zlib and I found that comparing with erlang driver it's around 30 % faster for doing the same job.
> After other investigations on zlib I found some interesting articles regarding intel and cloudflare patches and also zlibng that performs much better than 
> the original zlib. After I linked my NIF with this zlib libraries I got a gain of around 69 % compared with erlang driver. 
> 
> The testing script is here: https://github.com/silviucpp/ezlib/blob/master/testing/benchmark.erl <https://github.com/silviucpp/ezlib/blob/master/testing/benchmark.erl>
> 
> Basically reads a file line by line and compress it N times.
> 
> For example: 
> 
>     benchmark:run(ezlib,"file path here", 200, 6, 10, 1). 
>     benchmark:run(erlang,"file path here", 200, 6, 10, 1).
> 
> This is compressing the file 200 times with a compression level of 6 window size 10 and memory level 1. First one using my library second one using erlang driver.
> 
> Some benchmark results you can see on the https://github.com/silviucpp/ezlib <https://github.com/silviucpp/ezlib>
> 
> I can understand that the erlang driver api is generic and allows you to customize a lot if things and mine it's not and it's built 
> around my need to use it with ejabberd but still I'm almost sure if I change the interface the performance difference will be the same. 
> 
> Maybe my benchmark is not realistic or I'm missing something. 
> Feedback it's welcome.
> 
> Silviu
>  
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