SMT vs. multiprocessor chip [Eggers et al.]
SMT obtained better speedups than the (CMP) chip multiprocessors- in contrast to results of Hammond et al.!!Eggers et al. compared 8-issue, 8-threaded SMTs with four 2-issue CMPs.Hammond et al. compared 12-issue, 8-threaded SMTs with eight 2-issue CMPs.
Eggers et al.:
- Speedups on the CMP were hindered by the fixed partitioning of their hardware resources across the processors.
- In CMP processors were idle when thread-level parallelism was insufficient.
- Exploiting large amounts of instruction-level parallelism in the unrolled loops of individual threads not possible due to CMP processors smaller issue bandwidth.
An SMT processor dynamically partitions its resources among threads, and therefore can respond well to variations in both types of parallelism, exploiting them interchangeably.