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Apple M1 CPU has 128 or 192 KiB instruction L1 cache for each core (important for latency/single-thread performance), depending on core type. This is an unusually large L1 cache for any CPU type (not just for a laptop); the total cache memory size is not unusually large (the total is more important for throughput) for a laptop, and much larger ...
The new 192 KB L1 cache in the Lion Cove core acts as a mid-level buffer cache between the L0 data and instruction caches inside the core and the L2 cache outside the core. It is focussed on reducing latency in the event of L0 data cache misses rather than needing to access the L2 cache.
Cache hierarchy, or multi-level cache, is a memory architecture that uses a hierarchy of memory stores based on varying access speeds to cache data. Highly requested data is cached in high-speed access memory stores, allowing swifter access by central processing unit (CPU) cores.
The resulting load on memory use is known as pressure (respectively register pressure, cache pressure, and (main) memory pressure). Terms for data being missing from a higher level and needing to be fetched from a lower level are, respectively: register spilling (due to register pressure : register to cache), cache miss (cache to main memory ...
AMAT's three parameters hit time (or hit latency), miss rate, and miss penalty provide a quick analysis of memory systems. Hit latency (H) is the time to hit in the cache. Miss rate (MR) is the frequency of cache misses, while average miss penalty (AMP) is the cost of a cache miss in terms of time. Concretely it can be defined as follows.
The execution time is the time for a cache access, and the memory stall cycles include the time to service a cache miss and access lower levels of memory. If the access latency, miss rate and miss penalty are known, the average memory access time can be calculated with: = +
Notably the L1 data cache latency has been reduced from five cycles that is on Sunny Cove to just three cycles on Cypress Cove by change from 8 way associativity on Sunny Cove to 12 way associativity On Cypress Cove. Intel claims an increase of 19% in IPC in Cypress Cove–based Rocket Lake processors compared to Comet Lake. [15] [16]
The L1 instruction cache remains the same at 32 KB but the L1 data cache is increased from 32 KB to 48 KB per core. Furthermore, the bandwidth of the L1 data cache for 512-bit floating point unit pipes has also been doubled. The L1 data cache's associativity has increased from 8-way to 12-way in order to accommodate its larger size.