Do commodity SMT processors need more OS research?

Abstract

The availability of Simultaneous Multithreading (SMT) in commodity processors such as the Pentium 4 (P4) has raised interest among OS researchers. While earlier simulation studies of SMT suggested exciting performance potential, observed improvement on the P4 has been much more restrained, raising the hope that OS research can help bridge the gap. We argue that OS research for current commodity Simultaneous Multithreading (SMT) processors is unlikely to yield significant benefits. In general, we find that SMT processor simulations were optimistic about cache and memory performance characteristics, while overlooking the OS overheads of SMT kernels versus uniprocessor kernels. Using measurement and analysis on actual hardware, we find that little opportunity exists for realistic performance gains on commodity SMT beyond what is currently achieved.