NFS Performance

[Rick Macklem]

> Rick
> Do you have more details on the issue is it 8.x only ? Can you point
> us to the stable thread abourt this ?
> 
The bug is in the krpc, which means it's 8.x specific (at least for NFS,
I'm not sure if the nlm used the krpc in 7.x?).

David P. Discher reported a performance problem some time ago when testing
the FreeBSD8 client against certain servers. (I can't find the thread, so
maybe it never had a freebsd-stable@ cc after all.)

Fortutnately John Gemignani spotted the cause (for at least his case, because
he tested a patch that seemed to resolve the problem). The bug is basically
that the client side krpc for TCP assumed that the 4 bytes of data that hold
the length of the RPC message are in one mbuf and don't straddle multiple mbufs.
If the 4 bytes does straddle multiple mbufs, the krpc gets a "garbage message
length" and then typically wedges and eventually recovers by starting a fresh
TCP connection up and retrying the outstanding RPCs.

I have no idea if George is seeing the same problem, but the 1.5minute logjams
suggest that it might. I emailed him a patch and, hopefully, he will report back
on whether or not it helped.

A patch for the above bug is "in the works" for head, rick