1/9/2024 0 Comments Private cache accessA modern processor design has multiple cores, and inside those cores will be at least one private cache (the L1) that only that core has access to. There is also the scope of private and shared caches. It means that if that data line is ever needed again, it isn’t too far away.Īn example of L1, L2, and a shared 元 on AMD's First Gen Zen processors Once the cache line is used, it is often ‘evicted’ from the closest level cache (L1) to the next level up (L2), or if that L2 cache is full, the oldest cache line in the L2 will be evicted to an 元 cache to make room. Caches exist because the CPU core wants data NOW, and if it was all held in DRAM it would take 300+ cycles each time to fetch data.Ī modern CPU core will predict what data it needs in advance, bring it from DRAM into its caches, and then the core can grab it a lot faster when it needs it. These are separated by capacity, latency, and power – the fastest cache closest to the execution ports tends to be small, and then further out we have larger caches that are slightly slower, and then perhaps another cache before we hit main memory. Caches: A Brief PrimerĪny modern processor has multiple levels of cache associated with it. What they’ve done instead might be an indication of the future of on-chip cache design. IBM Z is known for having big 元 caches, backed with a separate global L4 cache chip that operates as a cache between multiple sockets of processors – with the new Telum chip, IBM has done away with that – there’s no L4, but interestingly enough, there’s no 元. It’s a big interesting piece of kit that I want to do a wider piece on at some point, but there was one feature of that core design that I want to pluck out and focus on specifically. At Hot Chips last week, IBM announced its new mainframe Z processor.
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