Making Deep Learning Go Brrrr from First Principles
71 points
by tosh
4 hours ago
| 3 comments
| horace.io
| HN
tosh
3 hours ago
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> in the time that Python can perform a single FLOP, an A100 could have chewed through 9.75 million FLOPS

wild

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patmorgan23
2 hours ago
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Why are we comparing a programing language and a GPU. This is a category error. Programing languages do not do any operations. They perform no FLOPs, they are the thing the FLOPs are performing.

"The I7-4770K and preform 20k more Flops than C++" is an equally sensible statement (i.e. not)

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smasher164
3 minutes ago
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> This is a category error.

Okay, but surely you know what they actually mean right, or are you being willfully obtuse? They are comparing CPython (the main python implementation)'s implementation that runs on the CPU with a kernel running on the GPU.

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gchamonlive
1 hour ago
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> Why are we comparing a programing language and a GPU.

You are taking the statement too literally and forgetting it's a figure of speech, specifically metonymy.

When the author says it's millions of flops faster in a gpu than in an interpreteted programming language, it's not comparing them directly, but algorithms that run in them, so the substitution is the algorithms for the tools used to implement/run them.

It makes sense if you say "running similar logic -- like multiplying vectors and matrices -- on the CPU is millions of flops slower then on the GPU". There is no category error there.

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tosh
1 hour ago
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the sentence is ambiguous because "Python" can mean python + a certain library and even a different Python implementation

but I find it illuminating to compare what a certain hardware can do in principle (what is possible) vs what I can "reach" as programmer within a certain system/setup

in this case NVIDIA A100 vs "Python" that does not reach a A100 (without the help of CUDA and PyTorch)

another analogy:

I find it useful to be able to compare what the fastest known way is to move a container from A to B using a certain vehicle (e.g. truck) and how that compares to how fast a person that can not drive that truck can do it + variants of it (on foot, using a cargo bike, using a boat via waterway, …)

I'm also interested in how much energy is needed, how much the hw costs and so on

Often there are many ways to do things, comparing is a great starting point for learning more

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tosh
1 hour ago
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related to the truck analogy: an advantage of the way slower Python approach is: it does not need a GPU

that said: Python can get to more FLOPs by changing the representation: https://docs.python.org/3/library/array.html

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tosh
1 hour ago
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re comments:

yes of course this is apples to oranges but that's kind of the point

it shows the vast span between specialized hardware throughput IFF you can use an A100 at its limit vs overhead of one of the most popular programming languages in use today that eventually does the "same thing" on a CPU

the interesting thing is why that is so

CPU vs GPU (latency vs throughput), boxing vs dense representation, interpreter overhead, scalar execution, layers upon layers, …

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p1esk
1 hour ago
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A100 FP32 throughput “at its limit”: 19.5 TFLOP/s.

AMD EPYC 9965 FP32 throughput “at its limit”: 41.2 TFLOP/s (192 cores x 64 FP32 FLOP/cycle/core x 3.35GHz).

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tosh
1 hour ago
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A100: 312 TFLOP/s for FP16

but it is very impressive how far modern CPUs get as well (also in smart phones!)

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p1esk
44 minutes ago
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Intel Xeon 6980P: 128 cores x 1024 FP16 FLOP/cycle/core x 3.2 GHz: 419 TFLOP/s
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p1esk
3 hours ago
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This statement makes zero sense
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itishappy
57 minutes ago
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Which, lets be honest, is probably still being orchestrated by Python somewhere.

Python is 9.75 million times faster than Python.

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giancarlostoro
53 minutes ago
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I was researching if there was much benefit to using Rust or C++ over Python for AI, and turns out, the GPU doesn't care once the instructions are in because its an entirely different spec running on the GPU. The only thing you might save on is "startup" costs of getting your code into the GPU I guess? I assume that time cost is miniscule though, once its all in memory, nobody cares that you spent any time "booting it up" any more than how long Windows takes these days.
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BillStrong
1 minute ago
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As long as you don't keep calling out to the CPU, that is.

Tool calling, searches, cache movement if used, and even debug steps all stall the GPU waiting for the CPU.

There was a test of turning one of the under 1B Qwen3+ models into a kernel that didn't stall by the CPU as one GPU pass that saw quite a bit f perf lift over vLLM, I believe, showing this is an issue still.

Its been a month, so I don't remember more details than this.

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xyzsparetimexyz
3 hours ago
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Single core vs multi core accounts for much of this
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cdavid
2 hours ago
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Not really. GPU many cores, at least for fp32, gives you 2 to 4 order of magnitudes compared to high speed CPU.

The rest will be from "python float" (e.g. not from numpy) to C, which gives you already 2 to 3 order of magnitude difference, and then another 2 to 3 from plan C to optimized SIMD.

See e.g. https://github.com/Avafly/optimize-gemm for how you can get 2 to 3 order of magnitude just from C.

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p1esk
1 hour ago
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Theoretical FP32 performance of AMD EPYC 9965 is double that of A100: 41.2 TFLOP/s vs 19.5 TFLOP/s
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jdw64
3 hours ago
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Right now, all I know how to do is pull models from Hugging Face, but someday I want to build my own small LLM from scratch
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max-amb
2 hours ago
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If you want a written resource I have a blog post about the mathematics behind building a feed forward from scratch, https://max-amb.github.io/blog/the_maths_behind_the_mlp/. Kinda focuses on translation from individual components to matrix operations.
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kflansburg
2 hours ago
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If you aren't already aware, Karpathy has several videos that could get you there in a few hours https://www.youtube.com/@AndrejKarpathy
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jdw64
2 hours ago
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very thanks!
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glouwbug
2 hours ago
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It’s just linear algebra. Work your way from feed forward to CNN to RNN to LSTM to attention then maybe a small inference engine. Kaparthy’s llama2.c is only ~300 lines on the latter and it pragma simds so you don’t need fancy GPUs
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noosphr
3 hours ago
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>For example, getting good performance on a dataset with deep learning also involves a lot of guesswork. But, if your training loss is way lower than your test loss, you're in the "overfitting" regime, and you're wasting your time if you try to increase the capacity of your model.

https://arxiv.org/abs/1912.02292

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appplication
3 hours ago
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Generally, posting a link-only reply without further elaboration comes across as a bit rude. Are you providing support for the above point? Refuting it? You felt compelled to comment, a few words to indicate what you’re actually trying to say would go a long way.
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noosphr
3 hours ago
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>We show that a variety of modern deep learning tasks exhibit a "double-descent" phenomenon where, as we increase model size, performance first gets worse and then gets better.
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smallerize
1 hour ago
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Does this mean that if your model is "overfitting", the solution is to train for even more epochs?
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ForceBru
2 hours ago
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Right, isn't double descent one of the reasons why modern Extremely Large Language Models work at all? I think I heard somewhere that basically all today's "smart" (reasoning, solving math problems, etc) LLMs are trained in the "double descent" territory (whatever this means, I'm not entirely sure).
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SiempreViernes
1 hour ago
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No, double descent is a symptom of whatever it is that makes the deep models work at all. It's just the name for something you see happen when it works. The reason it works has something to do with how all those extra dimensions work as a regularisation term in the fit.
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