Num_samples trails to updata model?

Hi,I have a quesetion.if i set the config[num_samples] ,how they updata the model?

and ,if i want to use some works to get samples, and use multi GPU to train.

and when we set num_of_gpus_in_workers, then the GPUs will only be uesed in the phase about geting samples? is not train?

please tell me ,i will very thank you~~~

can you tell me some things?thank you!