Re: [sc-users] Re: TCP default?

[Glen Fraser <holaglen@xxxxxxxxx>]

Hmm, not sure why the test results didn’t show up in my mail (they do appear in the Nabble forum)… For the record, they should have read:

./tcp_lat 100 10000
message size: 100 octets
roundtrip count: 10000
average latency: 17770 ns
./udp_lat 100 10000
message size: 100 octets
roundtrip count: 10000
average latency: 17528 ns

On 20 Dec 2016, at 15:07, Glen Fraser <holaglen@xxxxxxxxx> wrote:

Julian Rohrhuber-3 wrote

good point. Careful benchmarking really might be necessary to decide this,
see e.g.
http://stackoverflow.com/questions/47903/udp-vs-tcp-how-much-faster-is-it

For fun, I looked for some latency benchmarking tests.  I came across  this
<https://github.com/rigtorp/ipc-bench>  .  He includes no UDP test, so I
added one (submitted as a pull request to his repo; in the meantime you can
see my forked version  here <https://github.com/totalgee/ipc-bench>  ).  A
quick test of the TCP and (now) UDP latency tests, give results (on my
MacBook Air) such as:



On my machine, the UDP/TCP latencies tend to be very similar, for a given
message size and iteration count.

Note that for the above test, the UNIX pipe latency was a mere 5400 ns
whereas UNIX domain sockets achieved about 7300 ns, about 2-3 times faster
than using localhost (TCP or UDP) network sockets.  Still, 18 microseconds
isn't too bad either...

Also note that it would be useful to look at the min and max latencies, not
just average.  If you only send one small packet, you'll see that the
latency can be quite large, around a couple of hundred microseconds.  The
average latencies go up when you do fewer roundtrips in a burst (i.e. this
test is not exactly representative of how SC would be sending data).

Still, it might be useful, especially to see that (on my machine at least)
the results look quite similar for TCP and UDP.

Glen.



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