[erlang-questions] UDP receive performance

[Danil Zagoskin]

Hmm, seems like the value should be very close to expected size.
Setting buffer to 2048 did not change anything significantly.
The results in my previous message are with {buffer, 2048} option left from
earlier experiments.

On Wed, Jun 20, 2018 at 8:06 PM Lukas Larsson <lukas@REDACTED> wrote:

> On Wed, Jun 20, 2018 at 1:56 PM Jonas Falkevik <
> jonas.falkevik@REDACTED> wrote:
>
>>
>> Are you adding the multicast network to the loop back interface? Using
>> some other interface that does not allow multicast traffic?
>>
>>
> I though I had, but apparently not.... I managed to reproduce the test
> case now.
>
> I also spent some time staring at the code in the inet_driver and realized
> what the problem was in there. It would seem that a performance/feature fix
> for SCTP in R15B inadvertently introduced this behaviour for UDP :( I've
> pushed a bug fix to that problem in the inet_driver to the same branch. In
> my tests the scheduler utilization goes form 71% to about 4% with both
> patches. With the fix in the inet driver, my allocator patch does not
> really do any difference for this specific testcase, but I'll keep that fix
> anyways as it is a "good thing". I should probably also add a benchmark for
> this so that it does not happen again....
>
> I'd also like to add that changing the test-case to use a smaller
> user-space buffer also has the same effect. So if anyone is running a
> performance critical UDP server that has set the "recbuf" to a high value,
> I really recommend that you lower the "buffer" size to something close to
> the max expected packet size. In the example that Danil provided I applied
> the following patch:
>
> diff --git a/udptest.erl b/udptest.erl
> index 16a1798..4edeef0 100644
> --- a/udptest.erl
> +++ b/udptest.erl
> @@ -33,7 +33,9 @@ send_packet(ID, S, Addr, Port) ->
>
>  start_reader(Addr, Port) ->
>    GwIP = {0,0,0,0}, % {127,0,0,1},
> -  Common =
> [binary,{reuseaddr,true},{recbuf,2*1024*1024},inet,{read_packets,100},{active,500}],
> +  Common = [binary,{reuseaddr,true},
> +            {buffer,1500}, %% 1500 is just an example value, don't just
> copy this. You need to know what you max UDP packet size will be.
> +            {recbuf,2*1024*1024},inet,{read_packets,100},{active,500}],
>    Multicast =
> [{multicast_ttl,4},{multicast_loop,true},{ip,Addr},{add_membership,{Addr,GwIP}}],
>    Options = Common ++ Multicast,
>    spawn(fun() -> run_reader(Port, Options) end).
>
> and the scheduler utilization dropped to about 4% there as well.
>
> Lukas
>
>

-- 
Danil Zagoskin | z@REDACTED
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