COSC 6385 Computer Architecture
Exercises
Name:_______________________________________
1. Caches
a) The average memory access time (AMAT) can be modeled using the
following formula:
AMAT = Hit time + Miss rate * Miss penalty
Name and explain (briefly) one technique for each of the three components of
the formula in order to decrease the average memory access time.
Pick one of each block:
Reducing Miss penalty:
- Multilevel caches: 1st level small, but at the speed of the CPU, 2nd level
larger but slower
- Critical word first: don’t wait until the entire cache-block has been load,
focus
- on the required data item: ask for the required data item, Forward the data
item to the processor, Fill up the rest of the cache block afterwards
- Early restart: don’t wait until the entire cache-block has been load, focus
- on the required data item: Fetch words of a cache block in normal order,
Forward the requested data item to the processor as soon as available, Fill up
the rest of the cache block afterwards
- Giving priority to read misses over writes
- Merging write buffer: Check in the write buffer whether multiple entries can
be merged to a single one
- Victim caches: fully associative cache between the ‘real’ cache and the
memory keeping blocks that have been discarded from the cache
- )onblocking caches
- Hardware prefetch of Instructions and Data
- Compiler controlled prefetching
Reducing Miss rate:
- Larger cache block size
- Larger caches
- Higher associativity
- Way prediction and pseudo-associative caches
- Compiler optimization
Reducing Hit time:
- Small and simple caches
- Avoiding address translation
- Pipelined cache access
- Trace caches
( 3 Pts)
