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Re:Why do CPUs have multiple cache levels? (2016) by Symmetry on Thursday May 16, 2024 @03:28PM (#40382158)
Are you including address translation in the area you're ascribing to the L1$ there? I haven't looked at detailed area numbers for recent Intel designs but having equal area for L1$ and L2$ seems really weird to me based on numbers from other designs I've seen.

I'm having a hard time mentally come up with a way a larger L1$ could be faster. Have more ways, sure. Or more read ports. Or more bandwidth. And I'm given to understand that Intel tags (or used to tag) instruction boundaries in their L1I$. But how do you reduce latency? Physically larger transistors can more quickly overcome the capacitance of the lines their destination and the capacitance of their destinations but a large cache makes the distance and line capacitance correspondingly larger. You can have speed differences with 6T versus 8T SRAM cell designs but as I understand it Intel went to use 8T everywhere in Nahelem for energy efficiency reasons. I guess maybe changes in transistor technology could have made them revisit that, but 8 transistors isn't that much physically larger than 6.

But in general there are a lot of complicated things about how the memory subsystem of a CPU work that are important to performance, add add a floor to how low a first level cache's latency can be, but they don't really contradict anything that was said in the article.

Re:Why do CPUs have multiple cache levels? (2016) by koolba on Thursday May 16, 2024 @07:20PM (#40384523)
> I'm having a hard time mentally come up with a way a larger L1$ could be faster.

It’s faster because you’re comparing a two completely different physical implementations. SRAM does not use capacitors. DRAM does. You trade speed for density.

Re:Why do CPUs have multiple cache levels? (2016) by gsliepen on Friday May 17, 2024 @04:50AM (#40387775)
Except that L2 cache is also SRAM. In fact, usually all RAM inside the CPU is SRAM, because the process for making DRAM is not very compatible with the process for making SRAM and the rest of the CPU. We are only just recently been seeing devices which merge DRAM and a CPU into one package, but internally it is still on different chips (for example, the Apple M1 processor).
Re:Why do CPUs have multiple cache levels? (2016) by bobmcnamara on Friday May 17, 2024 @07:43AM (#40388827)
eDRAM L4 has been a thing in some Intel designs, but other than that, you're absolutely right
Re:Why do CPUs have multiple cache levels? (2016) by Symmetry on Friday May 17, 2024 @08:39AM (#40389236)
Also a few IBM designs. An interesting thing is that IBM claimed that eDRAM was faster than SRAM for their particular design because at the scale they were using it the reduced size of the array increased speed more than eDRAM's access time decreased it.