I am hopelessly stuck on a homework problem, and I would love some help understanding it better. Here is what I was given:
What is the effective CPI?
It is my understanding that I need to calculate the miss penalty for each cache level.
Now I need to calculate the effective CPI. This is where I am a bit confused.
I believe the formula should be:
CPI = BaseCPI + (%L1 MR/Instr * L1 Miss Penalty) + (%L1 MR/Instr * %L2 MR/Instr * L2 Miss Penalty) + (%Global MR/Instr * L3 Miss Penalty)
If I do this, I get
CPI = 2.0 + (0.07 * 30) + (0.07 * 0.3 * 60) + (0.03 * 300) = 14.36
After emailing my instructor because no one in the class understood the 1-2 minute explanation of global and local, I was told that my answer is close, but wrong. If anyone could provide some insight, or even point me towards a good tutorial, I would be grateful. I can understand how to figure out effective CPI for 1 and 2 level caches. Making the jump to 3 confuses me.
What if it is like this : for a two level cache The effective CPI is:
CPi= CPI(normal)+MissRAteL1*MissPenaltyL2+GlobalMissRAte*TotalMissPenalty
then for three level cache it might be:
CPI=CPI+MissRateL1*MissPenaltyL2+(MISSRATEL2/MissRAteL1)(MissPEnaltyL1+MissPEnaltyL2)+GlobalMissRate(MissPEnaltyL1+MissPEnaltyL2+MissPEnaltyL3)
CPI=2+7%x60+(7%/30%)x(60+30)+3%x(300+60+90)..