GPU utilization problrm

[jwnirvana]

Hello. The num_worker is 1 to default, then the GPU utilization is around 25%. When the num_worker is 8, that is around 60%. However, a new problem occurs:
=====> epoch[0/300] iter: (369/371) cur_lr: 0.000997 loss: 1.175 time:0.23
=====> epoch[0/300] iter: (370/371) cur_lr: 0.000997 loss: 0.740 time:0.23
cityscapes_train.py:42: UserWarning: volatile was removed and now has no effect. Use with torch.no_grad(): instead.
input_var = Variable(input, volatile=True).cuda()
[0/500] time: 0.80
[1/500] time: 0.02
[2/500] time: 0.02
[3/500] time: 0.02
[4/500] time: 0.02
[5/500] time: 0.02
[6/500] time: 0.02
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[25/500] time: 0.02
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[72/500] time: 0.02
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[74/500] time: 0.02
[75/500] time: 0.02

I do not know what this means. Could you tell me that,please?
Thank you.