Thread-Level Parallelism - Computer Architecture: A Quantitative Approach - page 400

FIGURE 5.26 A comparison of SMT and single-thread (ST) performance on the eight-
processor IBM eServer p5 575 . Note that the y -axis starts at a speedup of 0.9, a perform-
ance loss. Only one processor in each Power5 core is active, which should slightly improve
the results from SMT by decreasing destructive interference in the memory system. The SMT
results are obtained by creating 16 user threads, while the ST results use only eight threads;
with only one thread per processor, the Power5 is switched to single-threaded mode by the
OS. These results were collected by John McCalpin of IBM. As we can see from the data, the
standard deviation of the results for the SPECfpRate is higher than for SPECintRate (0.13
versus 0.07), indicating that the SMT improvement for FP programs is likely to vary widely.
5.8 Putting It All Together: Multicore Processors and
Their Performance
In 2011, multicore is a theme of all new processors. The implementations vary widely, as does
their support for larger multichip multiprocessors. In this section, we examine the design of
four different multicore processors and some performance characteristics.