Tuning

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/

Install tuned package and activate the realtime profile. This profile will:
- Reserve some CPU cores solely for S2SS (Kernel cmdline: isolcpus=[cpu_numbers])
- Activate sub-profiles:
  - network-latency
  - latency-performance
- See /etc/tuned/realtime-variables.conf
- See /usr/lib/tuned/realtime/
S2SS configuration:
- affinity: Maps network card IRQs and threads to isolated cores
- priority: Increases priority of network packets and threads
Configure NIC interrupt coalescence with ethtool:

$ ethtool -C|--coalesce devname [adaptive-rx on|off] [adaptive-tx on|off] ...
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=

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

Server-grade CPU: Intel Xeon
- A multi-core systems allows parallization of send/receive paths.
Server-grade network cards: Intel PRO/1000
- These allow offloading of UDP checksumming to the hardware