Question: Why TCP echo benchmark so much faster than UDP echo benchmark? about cppserver

[chronoxor]

Yes, but in those time for us TCP/SSL sessions were more important, so I add analogical UDP benchmark just for brief comparison.
I'll think it over, maybe in near future we'll create benchmarking tests special for UDP.

[ne0phyte70]

Yes. I have also found this to be very surprising. Can the developer please comment? TIA

[chronoxor]

In TCP a stream buffer is used to put all outgoing messages together and send them in a batch with full IP packet. Batch mode is more effective.

In UDP a small datagram is send each time in a new IP packet which is not full.

It's just a kind of scenario. In other scenarios UDP could be more effective (e.g. broadcasting).

[ne0phyte70]

Thx for your reply. Wouldn't this be an apples to oranges comparison then?  Shouldn't the stream buffer be used (or not used) in both cases to get a fair comparison?  Thx. Sent from Yahoo Mail on Android On Sat, 9 Jan 2021 at 0:37, Ivan Shynkarenka<[email protected]> wrote: In TCP a stream buffer is used to put all outgoing messages together and send them in a batch with full IP packet. Batch mode is more effective. In UDP a small datagram is send each time in a new IP package which is not full. It's just a kind of scenario. In other scenarios UDP could be more effective (e.g. broadcasting). — You are receiving this because you commented. Reply to this email directly, view it on GitHub, or unsubscribe.

[ne0phyte70]

Thx for yr clarification. Sent from Yahoo Mail on Android On Sat, 9 Jan 2021 at 1:08, Ivan Shynkarenka<[email protected]> wrote: Yes, but in those time for us TCP/SSL sessions were more important, so I add analogical UDP benchmark just for brief comparison. I'll think it over, maybe in near future we'll create benchmarking tests special for UDP. — You are receiving this because you commented. Reply to this email directly, view it on GitHub, or unsubscribe.

[nicodemuz-zz]

With UDP packets fairly large, and with the benefit of a smaller header, the free´d capacity for more "packets" in batch mode doesn't explain a factor 100 in performance difference unless we go really close to 0 in packet size (payload size), or unless it is CPU limited and not throughput limited.

For 1 Gbps throughput limit, which should not be limit with test in same PC, a UDP packet totalling ~120 bytes including IP and UDP header should result in 1 million packets per second as each is ~1000 bits in size. But I am not getting close to those figures with UDP.

So is it a CPU constraint from CPU overhead at each packet transmission? I never did check the CPU usage...

By the way:
Appropriate send and receive buffer sizes on TCP could even things out, and disabling Nagle algorithm would also adress the stream vs datagram issues making UDP and TCP implementation more comparable.