Tokio's AsyncWrite trait once again has support for vectored writes in
Tokio 0.3.4 (see tokio-rs/tokio#3149.
This branch re-enables vectored writes in h2.
This change doesn't make all that big of a performance improvement in
Hyper's HTTP/2 benchmarks, but they use a BytesMut as the buffer.
With a buffer that turns into more IO vectors in bytes_vectored, there
might be a more noticeable performance improvement.
I spent a bit trying to refactor the flush logic to coalesce into fewer
writev calls with more buffers, but the current implementation seems
like about the best we're going to get without a bigger refactor. It's
basically the same as what h2 did previously, so it's probably fine.
We've adopted `tracing` for diagnostics, but currently, it is just being
used as a drop-in replacement for the `log` crate. Ideally, we would
want to start emitting more structured diagnostics, using `tracing`'s
`Span`s and structured key-value fields.
A lot of the logging in `h2` is already written in a style that imitates
the formatting of structured key-value logs, but as textual log
messages. Migrating the logs to structured `tracing` events therefore is
pretty easy to do. I've also started adding spans, mostly in the read
path.
Finally, I've updated the tests to use `tracing` rather than
`env_logger`. The tracing setup happens in a macro, so that a span for
each test with the test's name can be generated and entered. This will
make the test output easier to read if multiple tests are run
concurrently with `--nocapture`.
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
