Abstracting Multi-Core Topologies with MCTOP

Abstract

Portability and efficiency are usually antagonists in multicore computing. In order to develop efficient code, one needs to take into account the topology of the target multi-cores (e.g., for locality). This clearly hampers code portability. In this paper, we show that you can have the cake and eat it too.We introduce MCTOP, an abstraction of multi-core topologies augmented with important low-level hardware information, such as memory bandwidths and communication latencies. We show how to automatically generate MCTOP using libmctop, our library that leverages the determinism of cache-coherence protocols to infer the topology of multi-cores using only latency measurements.MCTOP enables developers to accurately and portably define high-level performance optimization policies. We illustrate several such policies through four examples: (i-ii) thread placement in OpenMP and in a MapReduce library, (iii) a topology-aware mergesort algorithm, as well as (iv) automatic backoff schemes for locks. We illustrate the portability of these optimizations on five processors from Intel, AMD, and Oracle, with low effort.

Bandwidth-Aware Page Placement in NUMA

“…While these works focus on single-node systems where two or more applications share the same CPU, BWAP targets multi-node NUMA systems where each node is exclusively allocated to one application at most. Works such as [7], [28] propose effective tools to characterize (either through an analytical model or through an empirical procedure) the NUMA topology. These can be integrated into BWAP to allow BWAP to devise a more accurate canonical distribution.…”