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Comment by qubex | Hacker News Reader

> Performance is so high now that I wouldn’t bother doing this for an extra 5-10%

I’m an economist and I’m fascinated by this statement.

Surely if something (‘performance’, in this case) is ‘high’ then getting a 5-10% proportion of it is better than getting the same proportion increase in performance on a lesser level (the bigger the baseline, the bigger that 5-10% extra performance is). So it’s apparently irrational: being willing to incur effort (cost) to get something that is worth a smaller amount and being unwilling to do it when the same effort/cost gets you more isn’t what one would expect.

But maybe it’s satisficing: maybe formerly the experience was endurable only when running at 110% of maximum, but now there’s no need to redline to get a decent experience?

Or maybe it’s the law of diminishing returns, utility approaching some kind of asymptote.

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If you're running a compute task that is slow and takes an hour, then 5% additional speed saves you 3 minutes. If the computer gets 2x faster, then an additional 5% improvement only saves you 1.5 minutes. So if utility is proportional to time (and hence inversely proportional to speed), then this makes sense.

To me, that comment and response looks like a microcosm of how economics does, or doesn't, understand its subject matter.

At a large enough N 5% to 10% is massive, at a small enough N 5% to 10% gets you closer to competitive, somewhere between though is where those extra percentage points are "meh".

For instance I run my computing on a TR 1950X and I could probably undervolt or overclock the chip but, to be honest, it's not worth the perceived "risk". Undervolting could break specific instructions in undetectable ways and the only way to be sure things haven't broken would be to run something like sandsifter [0] multiple times. Because I, and many others who would have the technical know how, write software on these systems it's not very much worth the headache. If I had a seperate system I built just for gaming or doing a specific task and I wanted to reduce how much I spent, or the power usage, etc undervolting would then shift out of headache -> super worth it.

The last thing I want to have to do is run every piece of code I need through godbolt and pray there's no AVX instructions that "may" be fishy.

I think this is largely why cloud providers don't do things like this as aggressively. They do it to some extent with custom off-roadmap chips but not controlled dynamically in userspace. If we can get something like this original post into the kernel that would be a massive win for everyone.

[0] - https://github.com/xoreaxeaxeax/sandsifter

An analogy with airplanes: you pay cubic dollars to fly faster at the high end.

That is, it's easy to build an airplane that flies at 90 knots. You can then clean up the aerodynamics a bit, burn a bit more fuel to get a bit more power to fly 110 knots. If you want to fly 130 knots, you probably need to add fairings and wheel pants and put in a bigger engine that burns even more fuel. It's very hard to get to 150 knots without retractable landing gear, a massive engine, or removing seats. To get to 200 knots you need 50% more cylinders or a turbocharger. To go past that you usually start looking at a turboprop at 10x the cost and 4x the fuel burn, then jets (...etc.)

Back to computers... doubling your power consumption and heat output for a 100% speed improvement is a perfect, linear improvement. If you need more performance, it's a fair trade. Even if you care about battery life, you should still make the trade, because drawing half as much power for twice as long still burns the same amount of total energy, so you don't gain anything by slowing down.

But would you double your power consumption and heat output for a 50% speed improvement? What about a 20% improvement?

It's the same idea. If the chip makers are setting voltages near the high-end, exponential cost, diminishing returns side of the curve, then you'll get more total "value" back by going back to the linear part of the curve, assuming you care about all of the variables, and not just "more speed at any cost."

> Or maybe it’s the law of diminishing returns, utility approaching some kind of asymptote.

It's exactly this. Many things have sublinear utility (Money is often assumed to have a log or square-root utility).

speed often has this effect magnified because what people actually care about is time and time is the inverse of speed. Lets say that doing task Z takes X + Y time. At some point increasing the performance of Y has no measurable gain in utility because X dominates.

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