NFS response time

Hi

We have a problem with our NFS server on Redhat 9. In case a program on the server uses high CPU, the NFS clients almost lock and nfs stops giving response until that program lowers its CPU usage. We tried to increase the priority of nfsd deamons with renice, and also tried to increase the number of nfsd threads, decreased the priority of the program using high CPU with renice, but none of them worked. How can we decrease this problem so that nfs does not lock?