How to check the bandwidth usage of nccl backend?

I am using nccl backend to send and recv pytorch tensor on my server.
And I am trying to use these command to check the bandwidth usage, is it corrent?
Fisrt I use


as my dist utils.
And then I print


lo is the network interface used for loop.
Then I use

sudo iftop -i lo -n -P

But the bandwidth is too small.
WHat should I do to check the bandwidth uses of dist.send and dist.recv?

bandwidth is a network interface term, if you want to measure dist.send and dist.recv speed I think you can send and receive some large tensors and measure latency in any suitable way like time.time()?