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 extremely 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.