Why is NFSv4 so slow?

[Rick C. Petty]

On Wed, Sep 01, 2010 at 11:46:30AM -0400, Rick Macklem wrote:
> > 
> > I am experiencing similar issues with newnfs:
> > 
> > 1) I have two clients that each get around 0.5MiB/s to 2.6MiB/s
> > reading
> > from the NFS4-share on Gbit-Lan
> > 
> > 2) Mounting with -t newnfs -o nfsv3 results in no performance gain
> > whatsoever.
> > 
> > 3) Mounting with -t nfs results in 58MiB/s ! (Netcat has similar
> > performance) ??? not a hardware/driver issue from my pov
> 
> Ok, so it does sound like an issue in the experimental client and
> not NFSv4. For the most part, the read code is the same as
> the regular client, but it hasn't been brought up-to-date
> with recent changes.

Do you (or will you soon) have some patches I/we could test?  I'm
willing to try anything to avoid mounting ten or so subdirectories in
each of my mount points.

> One thing you could try is building a kernel without SMP enabled
> and see if that helps? (I only have single core hardware, so I won't
> see any SMP races.) If that helps, I can compare the regular vs
> experimental client for smp locking in the read stuff.

I can try disabling SMP too.  Should that really matter, if you're not
even pegging one CPU?  The locks shouldn't have *that* much overhead...

-- Rick C. Petty