How to run Gem5 simulator in fs mode without cache?

Question

I am able to run gem5 in fs mode , but now i want to remove cache from the system. So what changes i need to do in gem5/configs/example/fs.py file to remove cache and run successfully.

Answer 1

Caches are disabled by default, use --caches --l2cache to enable them

Then the question comes down to how to observe if caches are on or off.

I've tried the following methods:

• look into m5out/config.ini.

  That file contains a representation of the system configuration as a tree.

  The following entries are only present if we pass the cache flags:

  [system]
  children=l2
  
  [system.cpu]
  children=dcache icache
  

• Run some benchmarks with and without caches, and notice that they are slower without caches.

  Here are some examples: https://github.com/cirosantilli/linux-kernel-module-cheat/tree/f3503b4cc810556df3c736d0a147cc54e05efc83#gem5-cache-size

• Look into the Linux kernel special file systems like /sys.

  Doesn't work currently unfortunately: Why doesn't the Linux kernel see the cache sizes in the gem5 emulator in full system mode?

Caches don't make much difference for the default ARM --cpu-type=AtomicSimpleCPU

You likely want to use --cpu-type=HPI

HPI is more detailed, which makes the simulation slower.

TODO understand AtomicSimpleCPU in more detail, and why caches don't matter there.

TODO check out for X86 DerivO3CPU vs AtomicSimpleCPU. Blocked on: https://github.com/cirosantilli-work/gem5-issues/issues/2