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Comment by guard-of-terra | Hacker News Reader

Another question, is CUDA actually fast enough?

Because in bitcoin mining, it's always ATI/AMD and OpenCL because ATI cards are like ten times faster than Nvidia cards. This is because of architecture differencies.

Does it not affect this postgres table-scanning task? I wonder if they did any benchmarks.

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AMD's advantage in Bitcoin mining was purely due to an architectural quirk: their shader cores supported bitwise rotation, but Nvidia's didn't. Bitwise rotation is a rare instruction outside of certain crypto algorithms (like SHA256!), so this really means very little for general-purpose performance.

http://www.extremetech.com/computing/153467-amd-destroys-nvi...

Scrypt too? Because Nvidia performance on scrypt is bad either.

"AMD's advantage in Bitcoin mining was purely due to an architectural quirk"

False. I authored a Bitcoin miner utilizing this quirk (bit_align). I was also the first to leverage another instruction exclusive to AMD (bfi_int): https://bitcointalk.org/?topic=2949 bit_align "only" gave AMD a 1.7x advantage over Nvidia. The biggest perf gains (2x-3x!) came from the fact AMD has more execution units: https://en.bitcoin.it/wiki/Why_a_GPU_mines_faster_than_a_CPU... (I also authored this section of the wiki).

Don't use hashing/bitcoinmining/password cracking as your benchmark if that is not your workload.

This is because the hashing algorithm is highly dependent on integer rotate right instruction. AMD's implements it in 1 clock cycle, Nvidia in 3. So it's a special case.

NVidia cards do not efficiently implement bit rotation, while AMD cards do, and it happens to be the core part of the SHA algorithm used for bitcoin. In general for an arbitrary task they're fairly close in performance.

AMD cards dominate Nvidia in pretty much all password hash bruteforcing algos, even those that do not rely on bit rotation (bit_align). See http://golubev.com/gpuest.htm for example. It is true that another instruction helps in more cases (bfi_int which I talked about at http://blog.zorinaq.com/?e=43) but in general, AMD cards have a lot more raw integer and floating point compute resources (execution units) than Nvidia cards.

They're also moving away from the VLIW design with each successive generation, partly to better support more flexible GPGPU approaches.

That is really interesting. I had to look it up.

https://en.bitcoin.it/wiki/Mining_hardware_comparison

The fastest Nvidia showing is the Tesla S2070 which is a $18k Server with 8 GPU's! It can just barely keep up with a slightly over clocked single gpu HD7970.

I'm not a miner, so correct me if I'm wrong, but that seems like a bit of an apples-to-oranges comparison. Tesla cards (and the servers designed around them) are intended for specific use cases: mission-critical enterprise solutions and scientific HPC. As a result, they run slower processor and memory speeds in comparison to nVidia's own consumer products, use ECC memory, and are optimized for double-precision over single-precision performance. Mining with a Tesla is like gaming with a Quadro card.

There is nothing mission critical or 'enterprise' about Tesla/Fermi cards. You can crash them and lock up your whole machine. Even if you can reboot the OS the card may not respond and the rebooted OS won't see it, we sometimes have to physically shut the machine down to reset the Nvidia card. Nvidia is still a gaming company at heart and it's going to take a while for them to adjust to providing equipment that is meant to be reliable and not just fast.

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