Reiner Pope: evaluation

Transcript context

…I remember talking to an FPGA engineer at Jane Street, Clark, who helped me prep for the previous interview we did together. He was explaining why they use FPGAs. I imagine that for high-frequency trading, throughput is less important than latency, so having very specific control over the clock cycle in a deterministic way is the most important thing. Maybe it’d be interesting to talk about why you can’t just achieve that with an ASIC, or why you might use an FPGA to have deterministic clock cycles for high-frequency trading. Let’s consider the business case for an FPGA versus an ASIC. FPGAs and ASICs use largely the same conceptual model. You have a series of gates built from small primitives—ANDs, ORs, XORs—connected together with wires running in a fixed clock cycle. Anything you can express in an FPGA you can express in an ASIC too. It will be about an order of magnitude cheaper and have better energy efficiency on an ASIC than an FPGA. The trade-off is that the first FPGA costs you $10,000, whereas the first ASIC you make costs $30 million because it requires an entire tape-out. The business use case for an FPGA is when you want something that has very deterministic latency, fast runtime, and high parallelism, but you are going to change the workload frequently, maybe every month. You don’t want to pay that tape-out cost every time. How does an FPGA actually emulate the ASIC programming model in a fixed piece of hardware? At its core, it has the two components we just talked about. It has registers as storage devices, and it has lookup tables (LUTs) which provide all of the gates. Then there’s a third component. We have a swarm of these registers and LUTs, and they are connected by a big set of muxes. In front of every single one of these, we have a mux which selects an input from everywhere else. We have a whole bunch of different options feeding into all of these things. What this allows is essentially that when I program my FPGA, I can take all of these components and superimpose a particular wiring which goes through this LUT, feed it into another LUT, send it to this register, and then feed it into another LUT, or something like that. What I’ve drawn in orange is how you… FPGA means Field-Programmable Gate Array. The orange is what has been programmed in the field, whereas the white is all the wires that must exist in the FPGA in order to actually make the device in the first place. What does it mean to be programmed in the field?…

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