Systems and methods for forecasting behavior of caches include a hypothetical cache. The hypothetical cache is configured to emulate cache behavior, and performance metrics for the hypothetical cache are determined, where the performance metrics may be based on cache hits/misses. Performance metrics for a real cache of a processor core of a processing system may also be similarly determined. Behavior of the real cache is forecast based, at least, on performance metrics of the hypothetical cache, and in some cases, also on performance metrics of the real cache (e.g., based on a comparison of the performance metrics). Actions may be recommended and/or performed based on the forecast, where the actions include modifying the real cache size, associativity, or allocation for processor cores, migrating a task running in one processor cluster to another processor cluster, or for collecting data for the real cache for offline analysis.