Re: 2.6.15.1: UDP fragments >27208 bytes lost with ne2k-pci on DP83815 (was Re: persistent nasty hang in sync_page killing NFS (ne2k-pci / DP83815-related?), i686/PIII)

[Nix <nix@esperi.org.uk>]

On Mon, 30 Jan 2006, Trond Myklebust suggested tentatively:
> On Mon, 2006-01-30 at 16:55 +0000, Nix wrote:
>> On Sun, 29 Jan 2006, Trond Myklebust stipulated:
>> > As a general rule of thumb: if tcpdump/ethereal can see the reply on the
>> > client, then the engine socket should see it too. If tcpdump is indeed
>> > seeing those replies, you should check the RPC code by
>> > setting /proc/sys/sunrpc/rpc_debug to 1.
>> 
>> tcpdump is seeing them.
> 
> The complete packets, including all fragments?

Will check. Maybe one fragment or something is getting lost
(but if so, it's getting lost terribly *consistently*, as in,
every single time).

>> I *guess* that the `failed to lock transport' is the underlying error...
>> time to add some debugging and find out what task is locking the
>> transport. Back soon, must rebuild the kernel and reboot to clear this
>> lock ;)
> 
> Nope. The congestion window is 1 request, and you do indeed appear to
> have one request on the "pending" queue. The problem in the above trace
> is a complete lack of data_ready messages, meaning that the socket is
> never seeing any complete packets come in.

O*kay*. I'll do some tcpdumps on both sides and compare them.


... you are quite right. I'm mounting with an rsize and wsize of 32768
(i.e., the default negotiated between a recent Linux NFS client and
kernel server), and, completely consistently, 31504 bytes are sent and
*only 27208 bytes are received*. This is so consistent that there's no
way that this could be due to network congestion (unless it's getting
jammed up inside the receiving NIC or something: it's an NE2K card and
they're rather crap so maybe the card is just too slow: my determination
to replace the card has just gone up a notch. But nonetheless if it was
getting lost by the card I'd see TCP retransmissions, which `netstat -s'
assures me I do not).

This explains why I don't see a problem with DNS: the number of DNS
packets >27208 bytes can be counted on the fingers of one foot.

Captures are available, but I gathered about half a minute's traffic
so they're quite large (1Mb apiece).

Tim? Any ideas? Is anyone else with this card seeing this problem?

-- 
`I won't make a secret of the fact that your statement/question
 sent a wave of shock and horror through us.' --- David Anderson
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