[ENet-discuss] enet is dropping packets

[Soren Dreijer]

Hi there,

I've recently run into an issue with my enet-powered server. When the server
gets under heavy load, I'm starting to see unsuccessful connection attempts
to the server. I've used tcpdump on the box and I see the enet connection
packets coming in, but they're never processed by the server and the
connection is never established.

Looking at /proc/net/udp, I see a large number of dropped packets (>1000)
and I'm guessing that's the issue. That is, I'm thinking enet isn't reading
the packets from the UDP receive buffer fast enough and the kernel ends up
dropping the new packets.

One thing I can do is to increase ENET_HOST_RECEIVE_BUFFER_SIZE, of course,
but I'm more worried why the server is already bogged down with only about
124 clients connected.

That leads me to enet_host_service(). I'm running the enet event loop in a
dedicated thread and I specify a timeout of 1ms whenever I call
enet_host_service() to avoid the event loop thread spinning 100% CPU in case
there's nothing to read. I assume that means I will only read one event per
1ms, right? 

Is there a way to improve that, i.e. have enet_host_service() wait _up to_
1ms, but otherwise return as soon as there is data to process? It seems a
little backwards to me that the timeout value isn't just an upper bound on
the wait time in case nothing is received.

Cheers,
Soren