So called timing anomalies are phenomena in processors where changes of the local worst-case execution time (WCET) do not correspond to changes of the global WCET. Timing anomalies are problematic for timing analysis, since they make it challenging to use abstract hardware models that still lead to safe and tight WCET bounds. In this paper, we refine and categorize the conditions for timing anomalies, distinguishing between triggers and amplifiers, which communicate via processor state only. We use that distinction to present the theoretical approaches for countermeasures against timing anomalies. Then we establish a sufficient condition to avoid timing anomalies from pipeline scheduling decisions. Based on this condition, we modify a standard postpass instruction scheduler to avoid the accumulation of timing effects. This modified scheduler is evaluated for several experimental out-of-order architectures using the Mälardalen WCET benchmark suite. The results are promising.
Contact Albrecht at:
Dipl.-Ing. Albrecht Kadlec
Institute of Computer Engineering
Vienna University of Technology
A-1040 Vienna, Austria
albrecht at vmars.tuwien.ac.at