BUG/MEDIUM: mux-h2: split the stream's and connection's window sizes
The SETTINGS frame parser updates all streams' window for each
INITIAL_WINDOW_SIZE setting received on the connection (like h2spec
does in test 6.5.3), which can start to be expensive if repeated when
there are many streams (up to 100 by default). A quick test shows that
it's possible to parse only 35000 settings per second on a 3 GHz core
for 100 streams, which is rather small.
Given that window sizes are relative and may be negative, there's no
point in pre-initializing them for each stream and update them from
the settings. Instead, let's make them relative to the connection's
initial window size so that any change immediately affects all streams.
The only thing that remains needed is to wake up the streams that were
unblocked by the update, which is now done once at the end of
h2_process_demux() instead of once per setting. This now results in
5.7 million settings being processed per second, which is way better.
In order to keep the change small, the h2s' mws field was renamed to
"sws" for "stream window size", and an h2s_mws() function was added
to add it to the connection's initial window setting and determine the
window size to use when muxing. The h2c_update_all_ws() function was
renamed to h2c_unblock_sfctl() since it's now only used to unblock
previously blocked streams.
This needs to be backported to all versions till 1.8.
1 file changed