Tuning

This page is not directly related to VILLASnode. It describes several ways to optimize the host system for running real-time applications like VILLASnode.

Operating System and Kernel

For minimum latency several kernel and driver settings can be optimized. A PREEMPT_RT patched Linux kernel is recommended. Precompiled kernels for Fedora can be found here: http://ccrma.stanford.edu/planetccrma/software/

1. Tune overall system performance for real-time:
   1. Install a PREEMPT_RT patched Linux kernel.
   2. Use the tuned tool for improving general real-time performance.
      • Please adjust the setting isolated_cpucores according to your hardware.
      • Enable the following realtime tuned profile

$ dnf install tuned-profiles-realtime
$ echo "realtime" > /etc/tuned/active_profile
$ echo "isolated_cpucores=6-7" >> /etc/tuned/realtime-variables.conf
$ systemctl enable tuned && systemctl start tuned

1. Optimize the VILLASnode configuration.
   1. Map NIC IRQs (see setting affinity (integer)).
   2. Map Tasks (see global setting affinity (integer)).
   3. Increase priority of server task (nice(2)) (see global setting priority (integer)).
   4. Increase BSD socket priority (see global setting priority (integer) for node-type Sockets).
2. Configure NIC interrupt coalescence with ethtool: ethtool --coalesce eth0 adaptive-rx off adaptive-tx off
3. Configure NIC kernel driver in /etc/modprobe.d/e1000e.conf:

# More conservative interrupt throttling for better latency
# https://www.kernel.org/doc/Documentation/networking/e1000e.txt
option e1000e InterruptThrottleRate=

Hardware

This are some proposals for the selection of appropriate server hardware:

• Server-grade CPU: Intel Xeon
  • A multi-core system enables true paralell execution of multiple send / receive paths.
• Server-grade network cards: Intel PRO/1000
  • These allow offloading of UDP checksumming to the hardware