CA 714CA Midterm Review.ppt
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1、CA 714CA Midterm Review,C5 Cache Optimization,Reduce miss penalty Hardware and software Reduce miss rate Hardware and software Reduce hit time Hardware Complete list of techniques in figure 5.26 on page 499,C5 AMAT,Average memory access time= Hit time + miss rate * miss penalty + Useful in focusing
2、on the memory performance Not the over all system performance Left out CPIbase in the calculation,C5 CPI,CPI calculation used for over all system performance comparison, such as speedup of computer A to computer BCPI = CPIbase + Penalty CPIbase is the CPI without the special case penalty. Penalty is
3、 the penalty cycle per instruction,C5 CPI Example,CPI Calculation Example: CPI for two leveled cache. Assume unified L2 and separate instruction and data cache. CPI = CPIbase +Penalty CPIbase depends on the program and processor. Penalty = L1 miss penalty + L2 miss penalty L1 miss penalty = data L1
4、miss penalty + instruction miss penalty Data L1 miss penalty = data L1 access per instr * data L1 miss rate * data L1 miss penalty. Instruction miss penalty = instruction L1 access per instr * instruction L1 miss rate * instruction L1 miss penalty. L2 miss penalty = L2 access per instr * L2 miss rat
5、e * L2 miss penalty. L2 access per instr = instruction L1 access per instr * instruction L1 miss rate + data L1 access per instr * data L1 miss rate,C5 Virtual Memory,Easier to program in virtual memory Additional hardware needed to translate between the two OS is usually used to translate the two T
6、LB is used to cached the translation result for faster translation.,Cpu virtual address,$ virtual/physical address,Mem physical address,TLB,Virtual address,Physical address,C5 VM,CPI calculation for memory with VM CPI = CPIbase + Penalty Penalty = TLB miss penalty cycle per instruction= TLB miss per
7、 instruction * penalty cycle per TLB miss= TLB access per instruction * TLB miss rate * penalty cycle per TLB missTLB access per instruction is for both data and instruction access.,C7 Disk,Average disk access time = average seek time + average rotational delay + transfer time + controller overhead
8、Average rotational delay = time for platter to rotate half a cycle Transfer time = size of access / transfer speed Transfer speed = rotational speed * size of tracks Assuming the bit are read off continuously as the disk head pass over it.,C7 RAID,Use small disks to build a large storage system Smal
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