Low latency on the filer, but very high latency on VM guest

We have perofrmance issue.

The NFS datastore has <5 ms latency on the filer, but >80ms on VM guest as shown in vCenter. To me, the performance issue is not caused by the filer.

But, what steps should I take to investiage and find out the root cause, either on the filer side, VM guest, or both?

Thanks!