Re: [External⚠] Re: Unbound DATA frames in HTTP/3 proposal

On Thu, Oct 9, 2025 at 11:09 AM Demi Marie Obenour <demiobenour@gmail.com>
wrote:

> I would like to see proper benchmarks, though.


This would certainly depend on the details and constraints of the
implementation stack.

Two contrasting examples on a TCP-to-HTTP/3 CONNECT proxy illustrate the
range:

When the proxy uses a well-integrated library or set of libraries that
stream data transparently through kernel sockets and library layers, with
64Kb TCP segmentation offload and large enough buffers, the impact of
HTTP/3 DATA framing is minimal. The savings are limited to a few bytes on
the wire every few dozen packets.

At the other extreme, when data is forwarded entirely in user space
performing zero-copy transfers from a correctly ordered TCP packet into
HTTP/3 CONNECT stream, the situation changes. If the implementation can
reuse the received TCP header buffer to encode UDP and QUIC headers, the
additional HTTP/3 DATA framing can determine whether a memory copy of the
data is required. Depending on destination connection id length and size of
varint encoded integers, the requirement to add HTTP/3 DATA framing could
push the size of combined UDP/QUIC/HTTP/3 overhead beyond the size of the
original TCP header, resulting in a memory copy of the proxied data.
Depending on various other factors this may reduce throughput by ~5-10%.
Some zero-copy architectures allow reserving per-packet headroom
to mitigate this, but some don't.

I'm sure a similar range exists with other applications encapsulating data
into HTTP/3 streams.


Best Regards,
Yaroslav

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