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12GB/s seems a bit slow. I'd expect the only bottleneck to be memory bandwidth.

A dual channel DDR4 system memory bandwidth is ~40GB/s, and DDR5 ~80GB/s.

Since this operation requires both a read and a write, you'd expect half that.



> A dual channel DDR4 system memory bandwidth is ~40GB/s, and DDR5 ~80GB/s.

It's impossible to saturate the memory bandwidth on a modern CPU with a single thread, even if all you do is reads with absolutely no processing. The bottleneck is how fast outstanding cache misses can be satisfied.

The article even links to a benchmark that attempts to measure what it calls "sustainable memory bandwidth": https://www.cs.virginia.edu/stream/ref.html




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