nfsd becomes slow when machine CPU usage is at or over 100% on STABLE/13

From: Yoshihiro Ota <>
Date: Wed, 09 Mar 2022 08:46:01 UTC

I'm on stable/13 with latest code base.
I started testing pre-13.1 branch.

I noticed major performance degrades with NFS when all CPUs are fully utilized.

This happends with stable/13 but not releng/13.0 nor releng/12.3.

I had NFS server with above versions and rsynced nfs mount to ufs mount on NFS clients.
My NFS server has 4 cores.
When I had load average of 3 with make buildworld -j3, NFS server was fine.
After adding another 1 load, NFS server throughput came down to about 10% of before.
After taking back to 3 load avg, performance recovered and down again after getting over 4.
Disk was fully avaiable for rsync; buildworld was done on another disk.

Someone told me his smbfs was also slow and he suspected TCP/IP regression instead of NFS, by the way.