confused about GPU-util

[ffmpbgrnn]

Hi,
I tried to run goolenet_cudnn and found that GPU utilization of my 4 K20s would be 0% sometimes.

At first, I thought it might be due to slow I/O and I transferred the whole imagenet dataset to SSD and increased the number of threads for data loading with -nDonkeys 10.

But the problem still happens. However, GPU utilization of VGG-A is quite stable, so is Alexnet.

Any thoughts? Thank you very much!