tree 0868c1a11daf4020cd3082a5a2c2a4a694b4118e
parent 60f62682b1efc4483f86525a63b8af3cc84f87ef
author Willy Tarreau <w@1wt.eu> 1558858108 +0200
committer Willy Tarreau <w@1wt.eu> 1558863199 +0200
encoding latin1

MAJOR: mux-h2: switch to next mux buffer on buffer full condition.

Now when we fail to send because the mux buffer is full, before giving
up and marking MFULL, we try to allocate another buffer in the mux's
ring to try again. Thanks to this (and provided there are enough buffers
allocated to the mux's ring), a single stream picked in the send_list
cannot steal all the mux's room at once. For this, we expand the ring
size to 31 buffers as it seems to be optimal on benchmarks since it
divides the number of context switches by 3. It will inflate each H2
conn's memory by 1 kB.

The bandwidth is now much more stable. Prior to this, it a test on
h2->h1 with very large objects (1 GB), a few tens of connections and
a few tens of streams per connection would show a varying performance
between 34 and 95 Gbps on 2 cores/4 threads, with h2_snd_buf() stopped
on a buffer full condition between 300000 and 600000 times per second.
Now the performance is constantly between 88 and 96 Gbps. Measures show
that buffer full conditions are met around only 159 times per second
in this case, or rougly 2000 to 4000 times less often.