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Wednesday
Sep302015

Strategy: Taming Linux Scheduler Jitter Using CPU Isolation and Thread Affinity

When nanoseconds matter you have to pay attention to OS scheduling details. Mark Price, who works in the rarified high performance environment of high finance, shows how in his excellent article on Reducing system jitter.

For a tuning example he uses the famous Disrupter inter-thread messaging library. The goal is to keep the OS continuously feeding CPUs work from high priority threads. His baseline test shows the fastest message is sent in 76 nanoseconds, 1 in 100 messages took longer than 2 milliseconds, and the longest delay was 11 milliseconds.

The next section of the article shows in loving detail how to bring those latencies lower and more consistent, a job many people will need to do in practice. You'll want to read the article for a full explanation, including how to use perf_events and HdrHistogram. It's really great at showing the process, but in short:

  • Turning off power save mode on the CPU reduced brought the max latency from 11 msec down to 8 msec.
  • Guaranteeing threads will always have CPU resources using CPU isolation and thread affinity brought the maximum latency down to 14 microseconds.

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