TimerShield: Protecting High-Priority Tasks from Low-Priority Timer Interference

Patel, P. and Vanga, Manohar and Brandenburg, Björn B.
(2017) TimerShield: Protecting High-Priority Tasks from Low-Priority Timer Interference.
In: 2017 IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS).
Conference: RTAS - IEEE Real-Time and Embedded Technology and Applications Symposium

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Abstract

Timer interference arises when a high-priority realtime task is delayed by a timer interrupt that is intended for a lower-priority task. We demonstrate that high-resolution timers, as exposed for instance by Linux's hrtimer API, can cause substantial timer interference, which manifests as significantly increased response times and lowered throughput. To eliminate this source of unpredictability, we propose TimerShield, a priority-aware highresolution timer subsystem that selectively delays the servicing of lower-priority timer interrupts while a high-priority task is executing. We present the design and implementation of a fully functional TimerShield prototype in Linux PREEMPT RT and compare it against Linux's stock hrtimer subsystem on two different platforms (x86 and ARM). Our results show that TimerShield adds only little overhead, while completely eliminating the timing unpredictability and throughput degradation caused by unnecessary interrupts.

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