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

From: Yoshihiro Ota <>
Date: Sat, 19 Mar 2022 01:18:50 UTC

In short, it looks releng/13.1 doesn't have issues.
I haven't confirmed why fully but I'm suspecting debugging option on stable results in such performance penalty.

It look a while to build bisect kernels (due to some compile errors) and suspious test results - all of stable kernels seemd to have issues.

I had built several versions between releng/13.0 branch point to stable/13 (before releng/13.1 was created) and all of them had such performance degrade.

I started suspecting stable debug options and thus built releng/13.1 and tested.
I don't see NFS slowdown unlike stable/13.
releng/13.0 and releng/12.2 were also fine.


On Wed, 9 Mar 2022 14:39:39 +0000
Rick Macklem <> wrote:

> Yoshihiro Ota <> wrote:
> > Hi,
> >
> > 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.
> NFS performance is sensitive to RPC response time.
> Since this only happens when the COUs are busy, I'd suspect:
> - Kernel thread scheduling changes
> or
> - Timing of receive socket upcalls (which wake up the nfsd kernel threads).
> I suspect bisecting to the actual commit that causes this is the only way
> to find it.
> If you know of a working stable/13 that is more recent than 13.0, it would
> help. If not, you start at this commit (which did make socket upcall changes):
> commit 55cc0a478506ee1c2db7b2f9aadb9855e5490af3
> which was done on May 21, 2021.
> Maybe others can suggest commits related to thread scheduling (which I
> know nothing about).
> If you don't have the time/resources to bisect, I doubt this will get resolved.
> Good luck with it, rick
> 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.
> Hiro