With the maturing of the Realtime Preemption Patches (RT-Preempt) and their stepwise integration to the Mainline Linux kernel since version 2.6.18, we set out to answer the questions:

• How good is RT-Preempt with respect to the worst-case latency?
• How expensive is RT-Preempt with respect to a possible performance degradation of the system?

Taking that a lot of the preemption techniques… deployed have their origin in scalability demands and ot so much in realtime requirements, the most interesting case to look into is related to uni-processors on these we would expect the worst-case impact of RT-Preempt. To answer the question, we ran an tensive benchmark series on 2.8-GHz P4 and 1-GHz/600MHz VIA CIII boards, measuring general performance parameters as well as the realtime capabilities. For the latter, a trivial parport toggle program was used.

The results show that high-end CPUs are well supported by RT-preempt in general. Low-end systems pically of interest for automation and control, however, still need some work. In this paper we will outline the method used for evaluation and present the details of the results. This work was partly supported by the Open Source Automation Development Lab (OSADL).

Keywords: RT-Preempt, Jitter, Performance

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