NFSD high CPU usage

[Adam Guimont]

Rick Macklem wrote:
> I can think of two explanations for this.
> 1 - The server nfsd threads get confused when the TCP recv Q fills
>      and start looping around.
> OR
> 2 - The client is sending massive #s of RPCs (or crap that is
>      incomplete RPCs).
>
> To get a better idea w.r.t. what is going on, I'd suggest that
> you capture packets (for a relatively short period) when the
> server is 100% CPU busy.
> # tcpdump -s 0 -w out.pcap host <nfs-client>
> - run on the server should do it.
> Then look at out.pcap in wireshark and see what the packets
> look like. (wireshark understands NFS, whereas tcpdump doesn't)
> If #1, I'd guess very little traffic (maybe TCP layer stuff),
> if #2, I'd guess you'll see a lot of RPC requests or garbage
> that isn't a valid request. (This latter case would suggest a
> CentOS problem.)
>
> If you capture the packets but can't look at them in wireshark,
> you could email me the packet capture as an attachment and I
> can look at it after Apr. 10, when I get home.
>
> rick
>

Thanks Rick,

I was able to capture this today while it was happening. The capture is 
for about 100 seconds. I took a look at it in wireshark and to me it 
appears like the #2 situation you were describing.

If you would like to confirm that I've uploaded the pcap file here:

https://www.dropbox.com/s/pdhwj5z5tz7iwou/out.pcap.20150403

I will continue running some tests and trying to gather as much data as 
I can.

Regards,

Adam Guimont