gRPC server has high latencies, but uses almost no CPU about tonic

[LucioFranco]

So a lot of the actual request handling is done by hyper. Tonic is merely just a wrapper around types. That said, there have been many upstream changes to both hyper and tokio that have yet to be fully published. So I am personally waiting for both to get to a state where we should really start looking at optimizing performance until then it doesn't make much sense. Remember tonic is still in an alpha state but we are getting closer.

For perf possibly flamegraph?

[dominiquelefevre]

Hmm. Here is some throughput and latency data for various http frameworks: https://www.techempower.com/benchmarks/#section=data-r18&hw=ph&test=plaintext

It claims that tokio-minihttp has 3.1msec latency for HTTP GETs that return a fixed string "hello world". I see approx. 20msec latency for gRPC requests.

The test of Techempower uses a version of tokio that is not yet async/await-enabled. The 20ms latency, can it be a bug in async/await support in tokio or rust? Who do I talk at tokio/hyper about this?

A flamegraph would be great. How do I generate one for a rust program, or a tokio-based server?

[LucioFranco]

@dominiquelefevre right, tokio 0.1 is a bit different from tokio 0.2. In fact the scheduler has even been completely rewritten! https://tokio.rs/blog/2019-10-scheduler/

You could use this https://github.com/ferrous-systems/flamegraph

[dominiquelefevre]

Fixing #119 actually resolves this one.