Hardware Prefetching

Data Prefetching

Stream Buffer

• Whenever the prefetch mechanism detects a miss on a memory block, say A, it allocates a stream to begin prefetching successive blocks from the missed block onward. If the stream buffer can hold 4 blocks, then we would prefetch A+1, A+2, A+3, A+4 and hold those in the allocated stream buffer. If the processor consumes A+1 next, then it shall be moved "up" from the stream buffer to the processor's cache. The first entry of the stream buffer would now be A+2 and so on. This pattern of prefetching successive blocks is called Sequential Prefetching. It is mainly used when contiguous locations are to be prefetched. For example, it is used when prefetching instructions.

Instruction Prefetching

How to set up

Requirement

• JDK
• sbt

Project

Branch main is the cache without stream buffer.

The version with stream buffer:

git checkout hw_prefetch

You can also turn off prefetch by set:

val prefetch = false

in CacheConfig.scala

Generate Verilog:

cd chisel
make

P.S. make generates both Test.v and DCache.v, Test.v is for simulation; if you only need DCache.v, please run:

make cache