Interrupt/speed problems with 6.2 NFS server

[Doug Clements]

>
> Can you also send the output of ps -auxl?
>
> Also - do you notice this performance drop when running something like
> one of the network performance tools? I'd like to isolate the disk
> activity from the network activity for a clean test..
>

I tested this with iperf, and while I did see some nfs performance
degradation, it did not bog the machine or delay the terminal in the same
way. NFS requests were still processed in an acceptable fashion. It was
still responsive to commands and ran processes just fine. I would have to
say it performed as to be expected during iperf tests (on which I got about
85mbit/sec, which is also to be expected). Interrupts went down to about
2000/sec on em, but the machine did not hang.

Something I've noticed is that running 'systat -vm' seems to be part of the
problem. If I run the file copy by itself with rdist, it's fast and runs ok.
If I run it with systat -vm going, this is when the interrupts jump way up
and the machine starts to delay badly. Noticing this, I tried running
'sysctl -a' during the file copy, thinking there was some problem with
polling the kernel for certain statistics. Sure enough, sysctl -a delays at
2 spots. Once right after "kern.random.sys.harvest.swi: 0" and once again
after "debug.hashstat.nchash: 131072 61777 6 4713". While it is delayed here
(for a couple seconds for each one) the machine is totally hung. Maybe this
is a statistics polling issue? Maybe the machine is delayed just long enough
in systat -vm to make the nfs clients retry, causing a storm of interrupts?

Other systat modes do not seem to cause the same problem (pigs, icmp,
ifstat).

I do not think the ps or systat output is very accurate, since I can't get
them to run when the machine is hung up. I type in the command, but it does
not run until the machine springs back to life. I'm not sure how this will
affect measurements.

http://toric.loungenet.org/~doug/sysctl-a
http://toric.loungenet.org/~doug/psauxl
http://toric.loungenet.org/~doug/systat-vm

My real confusion lies in why there are still em interrupts at all, with
polling on.

Thanks!

--Doug