[erlang-questions] UDP receive performance

[Michael Stellar]

Looks good, does these patch already being committed upstream?

On Thu, Jun 21, 2018 at 8:56 PM Danil Zagoskin <z@REDACTED> wrote:

> 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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