Reiner Pope: evaluation

Transcript context

…It’s actually funny that you don’t think at the level of hardware. You just think, “Oh, I’ll just select element three,” and something as simple as that is in and of itself quite a complicated circuit. This is the first step of all of the hidden data movement costs that show up. We’re just going to compare. I have to pay this cost. I’ve got one mux here, and in fact I have two more copies of that for each of the three inputs to my multiply-accumulate operation. I have this cost, which is 3 x n x p AND gates over here, compared to p x q gates in the actual circuit that is doing the thing I care about. If we plug in actual numbers, with n being eight, I get 24 x p gates just in the data movement, compared to—if q is four—4 x p gates just in the multiply-adder. Where is the three coming from?…

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