tree c4b70908e033bf496df8a6c44bea5de159894676
parent e5891ca6c14c46d5f3a2169ede75b7fbb225216f
author Willy Tarreau <w@1wt.eu> 1576837134 +0100
committer Willy Tarreau <w@1wt.eu> 1578460238 +0100
encoding latin1

MEDIUM: dns: implement synchronous send

In dns_send_query(), there's no point in first waking up the FD, to get
called back by the poller to send the request and sleep. Instead let's
simply send the request as soon as it's known and only subscribe to the
poller when the socket buffers are full and it's required to poll (i.e.
almost never).

This significantly reduces the number of calls to the poller. A large
config sees the number of epoll_ctl() calls reduced from 577 to 7 over
10 seconds, the number of recvfrom() from 1533 to 582 and the number of
sendto() from 369 to 162.

It also has the extra benefit of building each requests only once per
resolution and sending it to multiple resolvers instead of rebuilding
it for each and every resolver.

This will reduce the risk of seeing situations similar to bug #416 in
the future.