Typical Throughput on 10Gbps LAN?

[mechaniputer]

Hi everyone,

I have written a simple round trip FastDDS app which communicates between two machines which are directly connected to each other (no router or switch) via 10Gbps ethernet.

I based it on the example described in [1]. I am using FastDDS 2.14.0. I know it is old, but I just want to understand the performance of what I currently have before changing things too much.

Things I already tried to improve performance:
I am using the RELIABLE_RELIABILITY_QOS. I am specifically interested in the performance of this setting, and I already know that other settings can improve throughput.

I tried the following with the default 1 second heartbeat period for all writers, and then I tried it with a 500 ns period as described in [2]. In both cases the results were similar. It is possible that there is a sweet spot and that I just need to do more tuning, but these results seem worse than I expected either way.

I also tried increasing the max reader+writer socket sizes, also as described in [2]. It likewise had no measurable effect.

Finally, I tried increasing the txqueuelen to 10000 as described in [2], again with no measurable effect.

Here is what my code is doing:
On the first machine, my "driver" app publishes a single sample of some configured size to topic A, and immediately calls DataReader::wait_for_unread_message() on topic B to wait for a response from the server. Once it receives this response, it takes the sample with DataReader::take_next_sample() and then loops again, sending another sample.

I also use std::chrono::steady_clock_now() before sending a sample and after receiving the response, in order to measure the round trip latency.

On the other machine, the "server" app calls DataReader::wait_for_unread_message() on topic A, takes the sample with DataReader::take_next_sample(), immediately sends the same received data back on topic B and re-loops.

What I am wondering:
What kind of throughput should I reasonably expect for various message sizes? At large sizes it appears remarkably slower than I expected. It runs at around 1 sample per second at a size of ~80 kilobytes. Beyond this size, it appears that packet loss becomes too extreme for meaningful results. What am I doing wrong? I'm wondering if my usage of the API is sub-optimal in some way.

Thanks in advance for any tips.

References:
[1] https://fast-dds.docs.eprosima.com/en/latest/fastddsgen/pubsub_app/pubsub_app.html#fastddsgen-pubsub-app
[2] https://fast-dds.docs.eprosima.com/en/latest/fastdds/use_cases/large_data/large_data.html

[MiguelCompany]

@mechaniputer

If the data type you are using is plain (i.e. POD), the first thing I would try is using take instead of take_next_sample (see here for reference).

The take_next_sample method makes a copy of the data. The take method returns a pointer to the internal Fast DDS memory (in case of plain types).

After changing the reading side, you could also do a similar change in the writer side. See documentation here

[MiguelCompany]

@mechaniputer Could you share the QoS of the DataWriter?

[mechaniputer]

Sure. Here is the code where I set it up:

DataWriterQos driver_qos;
driver_qos.reliable_writer_qos().times.heartbeatPeriod.seconds = 0;
driver_qos.reliable_writer_qos().times.heartbeatPeriod.nanosec = 500;
writer_ = publisher_->create_datawriter(topic_, driver_qos, &listener_);

[mechaniputer]

Is there anything wrong with the above QoS? What else might be the problem?

[mechaniputer]

Please, any advice would be appreciated. Please tell me if the QoS above is missing something that could be causing this or if it's something else. I am not an expert on using DDS. However my application is vary basic and should not be performing strangely. At times the duration of the pauses is 3 full seconds, on a single 64 byte sample write() invocation. I urgently need to collect realistic performance data and obviously something is wrong.

Edit: Here is the source repo for my code. Note that it is closely based on the HelloWorld example app. https://github.com/mechaniputer/LatencyBench-FastDDS

[MiguelCompany]

@mechaniputer Thanks for sharing the reproducer. We'll try to reproduce and send you some feedback