Sure, but that doesn't change the fact that you cannot simply plug that into a simple formula to get the e.g. the optimal block size for cache-blocking. To be

Sure, but that doesn't change the fact that you cannot simply plug that into a simple formula to get the e.g. the optimal block size for cache-blocking. To be more precise: you can try to figure out how cache size would affect optimal block size in theory and in practice this gets you pretty decent performance. But to get the last bit of performance out of the hardware you need to benchmark several configurations on the hardware and select the best one based on run time parameters like u-arch and cache size.