Confusing setting of validation frequency

🚀 Feature

Currently the validation frequency is set by check_val_every_n_epoch and val_check_interval of Trainer. The former one and latter one have an overlap in terms of frequency control actually. I propose use check_val_every_n_epoch and check_val_every_n_batches as the parameter:

check_val_every_n_epoch=10 is equivalent to check_val_every_n_epoch=10 previously check_val_every_n_epoch=0.1 is equivalent to val_check_interval=0.1 previously check_val_every_n_batches=10 is equivalent to val_check_interval=10.

And furthermore, these two options should be mutually exclusive. If one sets check_val_every_n_batches then shouldn’t set check_val_every_n_batches.

Motivation

I propose this because I get confused when I try to tweak the validation frequency and find two options for setting it…

[qiuhuaqi]

Why not merge the two flags together? e.g. keep only val_check_interval, use int to specify the number of batches, use float to specify in terms of epochs but allows >1.0

val_check_interval=3.0 => validation every 3 epochs, val_check_interval=10 => validation every 10 batches within an epoch in the unlikely usecase of val_check_interval=3.5 => validation every 3.5 epochs, (triggering validation_epoch_end at the end of epoch 4?)

This would also solve the mutual exclusiveness issue. Or would this complicate things too much?

[turian]

I am also interested in this