DOC: quic: add note on performance issue with listener contention
Complete quic4/quic6 bind lines by a note on performance issues due to
receiver socket contention. Suggest to use sharding to improve the
situation.
This should be backported up to 2.6.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index c3d4ea5..d0ce0ab 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -4563,9 +4563,15 @@
to receive a FD over the unix socket and uses it as if it
was the FD of an accept(). Should be used carefully.
- 'quic4@' -> address is resolved as IPv4 and protocol UDP
- is used.
+ is used. Note that QUIC connections attached to a
+ listener will be multiplexed over the listener socket.
+ With a large traffic this has a noticeable impact on
+ performance and CPU consumption. To improve this, you
+ should duplicate QUIC listener instances over several
+ threads, for example using "shards" keyword.
- 'quic6@' -> address is resolved as IPv6 and protocol UDP
- is used.
+ is used. The performance note for QUIC over IPv4 applies
+ as well.
You may want to reference some environment variables in the
address parameter, see section 2.3 about environment