Example: Harvard Architecture Unified vs Separate I&D(Harvard) Proc Unified 工- Cache-1 Proc D-Cache-1 Cache-1 Unified Cache-2 Unified Cache-2 Statistics (given in H&P) 16KB I&D: Inst miss rate=0. 64%, Data miss rate=6.47% 32KB unified: Aggregate miss rate=1.99% Which is better (ignore L2 cache)? Assume 33% data ops=75% accesses from instructions(1.0/1.33) hit time=1, miss time=50 Note that data hit has 1 stall for unified cache(only one port) AMATHarvard=75%X(1+0.64%X50)+25%X(1+647%X50)=205 AMAT Unified=75%X(1+199%X50)+25%X(1+1+1.99%X50)=2.24 2021-2-4 计算机体系结构Example: Harvard Architecture § Unified vs Separate I&D (Harvard) § Statistics (given in H&P): • 16KB I&D: Inst miss rate=0.64%, Data miss rate=6.47% • 32KB unified: Aggregate miss rate=1.99% § Which is better (ignore L2 cache)? • Assume 33% data ops Þ 75% accesses from instructions (1.0/1.33) • hit time=1, miss time=50 • Note that data hit has 1 stall for unified cache (only one port) AMATHarvard=75%x(1+0.64%x50)+25%x(1+6.47%x50) = 2.05 AMATUnified =75%x(1+1.99%x50)+25%x(1+1+1.99%x50)= 2.24 2021-2-4 计算机体系结构 47 I-Cache-1 Proc Proc Unified Cache-1 Unified Cache-2 D-Cache-1 Proc Unified Cache-2