A Memory-Level Parallelism Aware Fetch Policy for SMT Processors

Abstract

A thread executing on a simultaneous multithreading (SMT) processor that experiences a long-latency load will eventually stall while holding execution resources. Existing long-latency load aware SMT fetch policies limit the amount of resources allocated by a staffed thread by identifying long-latency loads and preventing the given thread from fetching more instructions - and in some implementations, instructions beyond the long-latency load may even be flushed which frees allocated resources. This paper proposes an SMT fetch policy that hikes into account the available memory-level parallelism (MLP) in a thread. The key idea proposed in this paper is that in case of an isolated long-latency had. i.e. there is no MLP the thread should be prevented from allocating additional resources. However, in case multiple independent long-latency loads overlap, i.e., there is MLP the thread should allocate as many resources as needed in order to fully expose the available MLP. The proposed MLP-aware fetch policy achieves better performance for MLP-intensive threads on an SMT processor and achieves a better overall balance between performance and fairness than previously proposed fetch policies