Pippy I can't see backward pass

Thank you @kwen2501!
I have one more question.
I also experimented the following code, but it seems not to work for pipelining.

when I set

DIMS = [28 * 28, 300, 100, 10]
DP_LAYERS = 2
PP_LAYERS = 1
#nnode=1, nproc_per_node=2

It works well for Dataparallel,
but when I set like below,

DIMS = [28 * 28, 300, 100, 10]
DP_LAYERS = 1
PP_LAYERS = 2
#nnode=1, nproc_per_node=2

or

DIMS = [28 * 28, 500, 250, 100, 50, 25, 10]
DP_LAYERS = 2
PP_LAYERS = 4
#nnode=2, nproc_per_node=4

It doesn’t work at all. could this problem be related to the issue I suggested at first? or did I set somethin incorreclty? If I need to post a new topic for this, I’ll do that.
Thank you.