Why is NFSv4 so slow?

[Rick C. Petty]

On Mon, Jun 28, 2010 at 12:35:14AM -0400, Rick Macklem wrote:
> 
> Being stuck in "newnfsreq" means that it is trying to establish a TCP
> connection with the server (again smells like some networking issue).
> <snip>
> Disabling delegations is the next step. (They aren't
> required for correct behaviour and are disabled by default because
> they are the "greenest" part of the implementation.)

After disabling delegations, I was able to build world and kernel on two
different clients, and my port build problems went away as well.

I'm still left with a performance problem, although not quite as bad as I
originally reported.  Directory listings are snappy once again, but playing
h264 video is choppy, particularly when seeking around: there's almost a
full second delay before it kicks in, no matter where I seek.  With NFSv3
the delay on seeks was less than 0.1 seconds and the playback was never
jittery.

I can try it again with v3 client and v4 server, if you think that's
worthy of pursuit.  If it makes any difference, the server's four CPUs are
pegged at 100% (running "nice +4" cpu-bound jobs).  But that was the case
before I enabled v4 server too.

-- Rick C. Petty