Cache Pirating: Measuring the Curse of the Shared Cache

We present a low-overhead method for accurately measuring application performance (CPI) and off-chip bandwidth (GB/s) as a function of available shared cache capacity. The method is implemented on real hardware, with no modifications to the application or operating system. We accomplish this by co-running a Pirate application that "steals" cache space with the Target application. By adjusting how much space the Pirate steals during the Target's execution, and using hardware performance counters to record the Target's performance, we can accurately and efficiently capture performance data for the Target application as a function of its available shared cache. At the same time we use performance counters to monitor the Pirate to ensure that it is successfully stealing the desired amount of cache. To evaluate this approach, we show that 1) the cache available to the Target behaves as expected, 2) the Pirate steals the desired amount of cache, and ) the Pirate does not bias the Target's performance. As a result, we are able to accurately measure the Target's performance while stealing up to an average of 6.8MB of the 8MB of cache on our Nehalem based test system with an average measurement overhead of only 5.5%.