Hi, With direct connect having been hacked in (err, I mean, "implemented"), it is (a lot) easier to do meaningful performance tests. h2load is a drop in replacement of ab that uses HTTP/2, and it allowed doing some easy profiling.
The good news is that the code seems to be well optimized already with few visible problems. The only issue is a very heavy sync contention on the socket wrapper object in Http2UpgradeHandler.writeHeaders and Http2UpgradeHandler.writeBody. The reason for that is when you do: h2load -c 1 -n 100 http://127.0.0.1:8080/tomcat.gif It ends up being translated in Tomcat into: process one hundred concurrent streams over one connection. Although h2load is not real world use, that's something that would need to be solved as a client can use of a lot of threads. There are two main issues in HTTP/2 that could be improved: 1) Ideally, there should be a way to limit stream concurrency to some extent and queue. But then there's a risk to stall a useful stream (that's where stream priority comes in of course). Not easy. 2) All reads/writes are blocking mid frame. It's not too bad in practice, but it's a useless risk, that's where async IO can provide an "easy" solution using a dedicated NIO2 implementation. Comments ? Rémy
