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13th Real-Time Linux Workshop from October 20 to 22 at the Faculty of Electrical Engineering, Czech Technical University in Prague

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Timing Analysis of a Linux-Based CAN-to-CAN Gateway

Michal Sojka, Czech Technical University in Prague
Pavel Píša, Czech Technical University in Prague
Oliver Hartkopp, Volkswagen Group Research
Ond Špinka, Czech Technical University in Prague
Zden Hanzálek, Czech Technical University in Prague

In this work, we have thoroughly analyzed timing properties of CAN-to-CAN gateway built with Linux SocketCAN subsystem.

We have evaluated the latencies induced by this gateway under various conditions, such as when traffic filters were in use, when the gateway was programmed to modify the frames, when various types of load were imposed on the gateway or when different kernels (both rt-preempt and vanilla) were used. The result is more than 600 publicly available graphs visualizing the observed behavior (http://rtime.felk.cvut.cz/can/benchmark/2/).

From these detailed results, we try to derive the general characteristics and some of them apply not only for the special case of CAN-to-CAN routing, but also for the whole Linux networking system because many mechanisms in networking stack are shared by all protocols. An example of that is the differences between in-kernel and user-space routing. We have also discovered several interesting anomalies.

The overall conclusion of our analysis is that the gateway provided by the SocketCAN project is in a pretty good shape. We believe that our results will help in merging the gateway into the mainline Linux version.