def mapped_update(i, opt_state, batch, state, rng):
"""This is a multi-device version of the update function above."""
# We assume all tensors have the first dimension = n_devices.
weights, slots, opt_params = opt_state
rng, subrng = jax_random.split(rng)
grad_fn = backend.grad(model_and_loss_call, has_aux=True)
grads, state = grad_fn(weights, batch, state, rng)
# We do a psum(1.0) here instead of `n_devices` since `n_devices` is just
# the number of devices on this host machine, however psum goes over all
# devices of all hosts (ex: a TPU pod) and we need to be averaging over all
# of them.
grads = jax.tree_util.tree_map(
lambda g: backend.psum(g, 'batch') / backend.psum(1.0, 'batch'), grads)
return optimizer.tree_update(
i, grads, weights, slots, opt_params), state, subrng
def mapped_update(i, opt_state, batch, state, rng):
"""This is a multi-device version of the update function above."""
# We assume all tensors have the first dimension = n_devices.
weights, slots, opt_params = opt_state
rng, subrng = jax_random.split(rng)
grad_fn = backend.grad(model_and_loss_call, has_aux=True)
grads, state = grad_fn(weights, batch, state, rng)
grads = jax.tree_util.tree_map(
lambda g: backend.psum(g, 'batch'), grads)
return optimizer.tree_update(
i, grads, weights, slots, opt_params), state, subrng
