[Icecast-dev] icecast performance on many concurrent low-bitrate streams

[Klaas Jan Wierenga]

Hi all,

I'm running an Icecast-2.2 server with at peak times some 50 sources and 500 concurrent listeners all using low-bitrate 16kpbs streams. I'm experiencing some connection losses at these peak times ("Client connection died" message in error.log).

The machine running Icecast has a 100Mbit connection to the internet. It is a Celeron 2.4Ghz machine with 1Gbyte of main memory. The CPU load at these peak times is normal at 0.4 (40%), the load is relatively high, averaging out at 0.4 with occasional peaks to 5.0.

I've analysed the ethernet packets on some of the listeners connections and found that Icecast sends many small packets (200-300) bytes. This led me to look at the interrupt rate during peak times. At these times the interrupt rate reaches 10000 interrupts per second.

Investigating a bit further I discovered that Icecast is turning off the Nagle algorithm by setting TCP_NODELAY option on the client sockets. This results in many small packets because a packet is sent as soon as possible without combining packets into larger packets. Would it be safe to turn on the Nagle algorithm (by removing the sock_set_nodelay() calls in appropriate places) to try to reduce the interrupt rate for many concurrent low-bitrate streams?

I would appreciate your response.

Regards,
Klaas Jan Wierenga