Aug 24 – 28, 2020
US/Pacific timezone

A theorem for the RT scheduling latency (and a measuring tool too!)

Aug 28, 2020, 7:00 AM
Refereed Track/Virtual-Room (LPC Virtual)

Refereed Track/Virtual-Room

LPC Virtual

LPC Refereed Track (Closed) LPC Refereed Track


Daniel Bristot de Oliveira (Red Hat, Inc.)


Defining Linux as an RTOS might be risky when we are outside of the kernel community. We know how and why it works, but we have to admit that the black-box approach used by cyclictest to measure the PREEMPT_RT’s primary metric, the scheduling latency, might not be enough for trying to convince other communities about the properties of the kernel-rt.

In the real-time theory, a common approach is the categorization of a system as a set of independent variables and equations that describe its integrated timing behavior. Two years ago, Daniel presented a model that could explain the relationship between the kernel events and the latency, and last year he showed a way to observe such events efficiently. Still, the final touch, the definition of the bound for the scheduling latency of the PREEMPT_RT using an approach accepted by the theoretical community was missing. Yes, it was.

Closing the trilogy, Daniel will present the theorem that defines the scheduling latency bound, and how it can be efficiently measured, not only as a single value but as the composition of the variables that can influence the latency. He will also present a proof-of-concept tool that measures the latency. In addition to the analysis, the tool can also be used in the definition of the root cause of latency spikes, which is another practical problem faced by PREEMPT_RT developers and users. However, discussions about how to make the tool more developers-friendly are still needed, and that is the goal of this talk.

The results presented in this talk was published at the ECRTS 2020, a top-tier academic conference about real-time systems, with reference to the discussions made in the previous edition of the Linux Plumbers.

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