tree 9a74729dd8167b96b0ada9353b214f8cbd269a2b
parent 06ae84a8ac58159ac1ac6168870821e71409ce09
author Willy Tarreau <w@1wt.eu> 1544594580 +0100
committer Willy Tarreau <w@1wt.eu> 1544611965 +0100
encoding latin1

MEDIUM: mux-h2: implement true zero-copy send of large HTX DATA blocks

This is similar to what was done for the H1 mux : when the mux's buffer
is empty and the htx area contains exactly one data block of the same
size as the requested count, and all window and frame size conditions are
satisfied, then it's possible to simply swap the caller's buffer with the
mux's output buffer and adjust offsets and length to match the entire
DATA HTX block in the middle. An H2 frame header has to be prepended
before the block but this always fits in an HTX frame header.

In this case we perform a true zero-copy operation from end-to-end. This
is the situation that happens all the time with large files. When using
HTX over H2 over TLS, this brings a 3% extra performance gain. TLS remains
a limiting factor here but the copy definitely has a cost. Also since
haproxy can now use H2 in clear, the savings can be higher.