A single-core cache hierarchy simulator written in python.

The goal is to accurately simulate the caching (allocation/hit/miss/replace/evict) behavior of all cache levels found in modern processors. It is developed as a backend to kerncraft, but is also planned to introduce a command line interface to replay LOAD/STORE instructions.

Currently supported features:

• Inclusive cache hierarchies
• LRU, MRU, RR and FIFO policies
• N-way cache associativity
• Write-allocate with write-back caches
• Non-write-allocate with write-through caches
• Write-combining with sub-blocking
• Tracking of cacheline states (e.g., using dirty bits)
• Speed (core is implemented in C)
• Python 2.7+ and 3.4+ support, with no other dependencies

Planned features:

• Report cachelines on all levels (preliminary support through backend.verbosity > 0)
• Report timeline of cache events (preliminary support through backend.verbosity > 0)
• Visualize events (html file?)
• Interface to Valgrind Infrastructure (see Lackey) for access history replay.
• (uncertain) instruction cache
• Optional classification into compulsory/capacity and conflict misses (by simulating other cache configurations in parallel)
• (uncertain) multi-core support

pycachesim is licensed under AGPLv3.

from cachesim import CacheSimulator, Cache, MainMemory

mem = MainMemory()
l3 = Cache("L3", 20480, 16, 64, "LRU")  # 20MB: 20480 sets, 16-ways with cacheline size of 64 bytes
mem.load_to(l3)
mem.store_from(l3)
l2 = Cache("L2", 512, 8, 64, "LRU", store_to=l3, load_from=l3)  # 256KB
l1 = Cache("L1", 64, 8, 64, "LRU", store_to=l2, load_from=l2)  # 32KB
cs = CacheSimulator(l1, mem)

cs.load(2342)  # Loads one byte from address 2342, should be a miss in all cache-levels
cs.store(512, length=8)  # Stores 8 bytes to addresses 512-519,
                         # will also be a load miss (due to write-allocate)
cs.load(512, length=8)  # Loads from address 512 until (exclusive) 520 (eight bytes)

cs.force_write_back()
cs.print_stats()

This should return:

CACHE *******HIT******** *******MISS******* *******LOAD******* ******STORE*******
   L1      1 (       8B)      2 (      65B)      3 (      73B)      1 (       8B)
   L2      0 (       0B)      2 (     128B)      2 (     128B)      1 (      64B)
   L3      0 (       0B)      2 (     128B)      2 (     128B)      1 (      64B)
  MEM      2 (     128B)      0 (       0B)      2 (     128B)      1 (      64B)

Each row refers to one memory-level, starting with L1 and ending with main memory. The 3 loads in L1 are the sum of all individual accesses to the cache-hierarchy. 1 (from first load) + 1 (from store with write-allocate) + 1 (from second load) = 3.

The 1 hit, is for bytes which were cached already. Internally the pycachesim operates on cache-lines, which all addresses get transformed to. Thus, the two misses throughout all cache-levels are actually two complete cache-lines and after the cache-line had been loaded the consecutive access to the same cache-line are handled as hits. That is also the reason why data sizes increase from L1 to L2. L1 is accessed byte-wise and L2 only with cache-line granularity.

So: hits, misses, stores and loads in L1 are byte-wise. Every other statistical information are based on cache-lines.

When using victim caches, setting victims_to to the victim cache level, will cause pycachesim to forward unmodified cache-lines to this level on replacement. During a miss, victims_to is checked for availability and only hit if it the cache-line is found. This means, that load stats will equal hit stats in victim caches and misses should always be zero.

While searching for more versatile cache simulator for kerncraft, I stumbled across the following:

• gem5: Very fully-featured full system simulator. Complex to extract only the memory subsystem
• dineroIV: Nice and simple code, but does not support exclusive caches and not available under open source license.
• cachegrind: Maintained and stable code of a well established open source project, but only supports inclusive first and last level caches.
• callgrind: see cachegrind
• SMPcache: Only supports one single cache and runs on Windows with GUI. Also not freely available.
• CMPsim: Was only academically published and source code never made available.
• CASPER: Was only academically published and source code never made available.