Dust: Pretraining Transformers Without Backpropagation
qlabs.sh68 points by E-Reverance 2 hours ago
68 points by E-Reverance 2 hours ago
Even though this is way more expensive than backprop, could a hybrid approach where you fine tune an existing checkpoint that's been backpropped unlock further gains? It would be cool to apply this to different stages and see if that affects the learning trajectory
It sounds like this is less computationally efficient than backprop, but more easily parallelizable. Is that fair?
Not necessarily, backprop is highly parallelizable since it is just a bunch of matrix mults.
Something like Dust skips the backward pass on backprop. But other techniques like Neural Predictive Coding can be completely asynchronous, each "weight" can fire independent of those far away from it. Innocenti, et. al have shown that NPC gradients converge to backprop within a certain "regime".
The win with asynchronous techniques like NPC is that you do not need the extreme co-ordination that backprop requires and hence should be computationally much easier given the right device.
Although at this point the industry has so much money in the forward-backward pass system that I doubt a backprop successor would win unless someone makes NPC hardware feasible and can prove scaling up to billions of params
The reason why I don't see the promise for ML-only applications is that the coordination backprop requires comes very cheap to us.
"Much easier given the right device" - the "right" there just isn't shaped like the devices we actually build. And the price of "not having backprop" is usually expending more FLOPs, getting worse sample efficiency, etc.
The biggest "device" that doesn't do backprop is the brain, and that's because the brain doesn't have the connectivity or the coordination to pull it off. Both of those are "expensive" for something like it to implement. Cheap for us though. We aren't stuck with neurons that only get locally available information and have to implement learning rules based on that. So, skill issue?
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