Computing Safe Contention Bounds for Multicore Resources with Round-Robin and FIFO Arbitration

Abstract

Numerous researchers have studied the contention that arises among tasks running in parallel on a multicore processor. Most of those studies seek to derive a tight and sound upper-bound for the worst-case delay with which a processor resource may serve an incoming request, when its access is arbitrated using time-predictable policies such as round-robin or FIFO. We call this value upper-bound delay ( $ubd$ ). Deriving trustworthy $ubd$ statically is possible when sufficient public information exists on the timing latency incurred on access to the resource of interest. Unfortunately however, that is rarely granted for commercial-of-the-shelf (COTS) processors. Therefore, the users resort to measurement observations on the target processor and thus compute a “measured” $ubd_{m}$ . However, using $ubd_{m}$ to compute worst-case execution time values for programs running on COTS multicore processors requires qualification on the soundness of the result. In this paper, we present a measurement-based methodology to derive a $ubd_m$ under round-robin (RoRo) and first-in-first-out (FIFO) arbitration, which accurately approximates $ubd$ from above, without needing latency information from the hardware provider. Experimental results, obtained on multiple processor configurations, demonstrate the robustness of the proposed methodology.