[erlang-questions] UDP client/server performance

Kenneth Lundin <>
Wed Aug 15 12:22:06 CEST 2012

Hi Ronny,

I think you are a little bit fast in drawing the conclusion that you
must look at other solutions
than just using the standard gen_udp module.

If you have found some real bottle neck in performance we should of
course try to find out why the difference between C and Erlang is so
big, I don't think it should be that big.

In case there is something unnecessarily inefficient going on when
using gen_udp we should
try to address that instead of looking at more complex and not so
general alternatives

A deeper analysis of what your test is doing would be good, is it
comparable with the C case?
Can the difference be explained etc.

I am not convinced that you will get better speed the alternative ways
you have been recommended. The socket code is written in C even when
you use gen_udp so I don't
really see the big difference. I also suppose you in reality want to
do something with the
data on the Erlang side and that would probably change the
characteristics. Another thing is if there is multiple cores involved

Kenneth , Erlang/OTP Ericsson

On 8/14/12, Ronny Meeus <> wrote:
> Is there any code available that implements a NIF to have access to UDP
> sockets?
> I have found the procket implementation but it looks like it is using
> a separate process to communicate with the socket. This sounds like
> overkill to me for this test.
> Ronny
> On Mon, Aug 13, 2012 at 10:29 PM, Ronny Meeus <>
> wrote:
>> Hello
>> I did a quick check.
>> - The values between 2 machines are comparable for Erlang.
>> - For the C code there is a difference: the async version drops from
>> 700Kpks/sec to 400Kpks/sec while the sync version drops from
>> 86Kpkts/sec to 10Kpkts/sec.
>> On Mon, Aug 13, 2012 at 9:42 PM, JD Bothma <> wrote:
>>> I'm curious:
>>> What are the numbers like (c versus erlang) when it's between two
>>> physical machines? Or between two (vmware or virtualbox, not xen)
>>> virtual machines?
>>> Or said otherwise: does the fact that it's the same machine, network
>>> stack and loopback interface affect the comparison between c and
>>> erlang?
>>> JD
>>> On 13 August 2012 21:11, Ronny Meeus <> wrote:
>>>> Hello
>>>> I have created a simple UDP based client/server application.
>>>> The code is available on bitbucket
>>>> (https://bitbucket.org/meeusr/erl-examples) in the networking
>>>> directory.
>>>> The server is just an echo server running in 1 process.
>>>> The client can behave like a sync client (sending 1 message and
>>>> waiting for the reply) or like an async client (sending X messages
>>>> before waiting for all the replies).
>>>> I see that my PC (Intel(R) Quad code i7 CPU 860  @ 2.80GHz) is able to
>>>> process something like 7K - 10K messages per second. Both the sync and
>>>> the async are in the same order of magnitude. Please note that I use
>>>> the loopback interface.
>>>> $ erl +sbt db
>>>> Erlang R15B01 (erts-5.9.1) [source] [64-bit] [smp:4:4]
>>>> [async-threads:0] [hipe] [kernel-poll:false]
>>>> Eshell V5.9.1  (abort with ^G)
>>>> 1> c(gen_udp_test).
>>>> gen_udp_test.erl:47: Warning: variable 'Data' is unused
>>>> gen_udp_test.erl:47: Warning: variable 'Msg' is unused
>>>> gen_udp_test.erl:62: Warning: variable 'Data' is unused
>>>> gen_udp_test.erl:62: Warning: variable 'Msg' is unused
>>>> {ok,gen_udp_test}
>>>> 2> gen_udp_test:start_server().
>>>> true
>>>> ...
>>>> 12> gen_udp_test:client_async(5000).
>>>> stop : 841482
>>>> ok
>>>> 13> gen_udp_test:client_async(6000).
>>>> stop : 1082679
>>>> ok
>>>> The timings are the number of usec for the processing of the X number
>>>> of messages (round-trip).
>>>> If I implement the same application in C (client and server are 2
>>>> applications), I see that the application performs an order of
>>>> magnitude better for the sync solution (86Kpkts/sec) and 100 times
>>>> better (700Kpkts/sec) for the async version.
>>>> The code for this is also available in the repo on bitbucket.
>>>> I know there this test is only looking to a part of the application
>>>> (transport of the data), but I find the difference rather big.
>>>> Is this normal or is there something wrong in my Erlang code?
>>>> Thanks.
>>>> Regards,
>>>> Ronny
>>>> _______________________________________________
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>>>> http://erlang.org/mailman/listinfo/erlang-questions
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