System Performance Equation

From PEL Wiki

Contents 1 DiskRAM Performance Equation 2 Levels to take into consideration 3 AMAT (Average Memory Access Time 4 Total Cycles equation

DiskRAM Performance Equation

I'd like to be able to characterize DiskRAM in one nice equation. These are the levels which could be accessed.

Levels to take into consideration

1. L1 Cache
2. L2 Cache
3. TLB
4. Page Tables (several memory accesses starting at the top)
5. DRAM
6. Disk
   1. O/S call
   2. Bus Commands
   3. Disk Access
      1. Hit OR
      2. Miss
         1. Seek Time
            1. Accelerate
            2. Coast
            3. Descelerate
            4. Settle
         2. Rotational Latency (1/2 rpm^-1)
   4. Transfer Time

AMAT (Average Memory Access Time

It looks like most people use: Average Memory Acess Time (AMAT) = hit_time + miss_rate * miss_penalty

then because the TLB is accessed in parallel... we should use

miss_penalty = dram_access + tlb_miss_rate * page_walk

Total Cycles equation

J. E. Smith's slides at SPEC workshop

Total Cycles = Ntotal/D +	((D-1)/2)*(miL1 + mbr + mL2)
	+ mic * ciL1
	+ mbr * (cdr + cfe)
	+ mL2 * (- W/D + clr + cL2)
Ntotal – total number of instructions
D – pipeline decode/issue/retire width
W – Window size
mic – i-cache misses
ciL1 – I cache miss latency
mbr – branch mispredictions
cdr – window drain time
mL2 – L2 cache misses (non-overlapped)
cfe – pipeline front-end latency
clr – load resoluton time