Discuss the pros and cons of shared vs. private L2 caches for both single-threaded, multi-threaded, and multiprogrammed workloads, and reconsider them if having on-chip L3 caches.

Both Barcelona and Nehalem are chip multiprocessors (CMPs), having multiple cores and their caches on a single chip. CMP on-chip L2 cache design has interesting trade-offs. The following table shows the miss rates and hit latencies for two benchmarks with private vs. shared L2 cache designs. Assume L1 cache misses once every 32 instructions.

Benchmark A misses-per-instruction Benchmark B misses-per-instruction Private 0.30% 0.06% Shared 0.12% 0.03%