Memory Behavior for an X11 Window System

We used memory reference traces from a DEC Ultrix system running the X11 window system from MIT Project Athena and several freely available X11 applications to measure different aspects of memory system behavior and performance. Our measurements show that memory behavior for X11 workloads differs in several important ways from workloads more traditionally used in cache performance studies. User instruction cache behavior is a major component in overall memory system delays, with significant competition within and between address spaces. User TLB miss rates are up to a factor of two higher than other ill-behaved integer workloads. Write-buffer stalls, data cache behavior, and uncached memory reads can be problematic for microbenchmarks, but they are not an issue for the realistic applications we tested.