As the number of cores per node increases in modern clusters, intra-node communication
efficiency becomes critical to application performance. We present a study of the traditional
double-copy model in MPICH2 and a kernel-assisted single-copy strategy with KNEM on
different shared-memory hosts with up to 96 cores. We show that KNEM suffers less from
process placement on these complex architectures. It improves throughput up to a factor of 2
for large messages for both point-to-point and collective operations, and significantly …