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2022-07-06 - 02:41

Dates and Events:

OSADL Articles:

2022-01-13 12:00

Phase #3 of OSADL project on OPC UA PubSub over TSN successfully completed

Another important milestone on the way to interoperable Open Source real-time Ethernet has been reached

2021-02-09 12:00

Open Source OPC UA PubSub over TSN project phase #3 launched

Letter of Intent with call for participation is now available

2016-11-12 12:00

Raspberry Pi and real-time Linux

Let's have a look at the OSADL QA Farm data

2016-09-17 12:00

Preemption latency of real-time Linux systems

How to measure it – and how to fix it, if it's too high?

Real Time Linux Workshops

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15th Real Time Linux Workshop, October 28 to 31, 2013 at the Dipartimento Tecnologie Innovative, Scuola Universitaria Professionale della Svizzera Italiana in Lugano-Manno, Switzerland

Announcement - Call for participation (ASCII)Hotels - Directions - AgendaPaper Abstracts - Presentations - Registration - Abstract Submission - Sponsors - Gallery

Investigating the Network Performance of a Real-Time Linux Kernel

Luca Abeni, University of Trento, Italy
Csaba Kiraly, University of Trento, Italy

The Linux kernel provides a high-performance networking subsystem by processing packets in soft-IRQ contexts. The network drivers use the so called "New API" (NAPI), according to which a hard-IRQ handler just disables the NIC interrupts and triggers a NET_RX soft-IRQ, which will receive the packets from the NIC and process them. If the number of network packets on the NIC is less than a specified threshold, the NIC interrupts are re-enabled, otherwise they are kept disabled and the soft-IRQ is armed again. This implements an interrupt mitigation mechanism that improves the throughput in presence of high packet rates. The preempt-RT patch transforms hard-IRQ handlers in kernel threads, in order to improve the system's determinism and reduce the kernel latencies. However, as usual there is a duality between high throughput and low latencies, and the threaded IRQ architecture risks to decrease the network performance.

This paper compares the network performance of a vanilla Linux kernel with the performance of a real-time version of the same kernel (based on Prempt-RT). Moreover, the impact of the network stack on the execution of real-time applications is evaluated. Finally, an alternative approach, based on processing network packets in the hard-IRQ thread instead of soft-IRQ context, is presented and evaluated, showing how it impacts the network performance and the predictability of real-time applications.