Network loss

[Rick Macklem]

John Baldwin wrote:
> On Tuesday, February 25, 2014 2:19:01 am Johan Kooijman wrote:
> > Hi all,
> > 
> > I have a weird situation here where I can't get my head around.
> > 
> > One FreeBSD 9.2-STABLE ZFS/NFS box, multiple Linux clients. Once in
> > a while
> > the Linux clients loose their NFS connection:
> > 
> > Feb 25 06:24:09 hv3 kernel: nfs: server 10.0.24.1 not responding,
> > timed out
> > 
> > Not all boxes, just one out of the cluster. The weird part is that
> > when I
> > try to ping a Linux client from the FreeBSD box, I have between 10
> > and 30%
> > packetloss - all day long, no specific timeframe. If I ping the
> > Linux
> > clients - no loss. If I ping back from the Linux clients to FBSD
> > box - no
> > loss.
> > 
> > The errors I get when pinging a Linux client is this one:
> > ping: sendto: File too large
> 
> EFBIG is sometimes used for drivers when a packet takes too many
> scatter/gather entries.  Since you mentioned NFS, one thing you can
> try is to
> disable TSO on the intertface you are using for NFS to see if that
> "fixes" it.
> 
And please email if you try it and let us know if it helps.

I've think I've figured out how 64K NFS read replies can do this,
but I'll admit "ping" is a mystery? (Doesn't it just send a single
packet that would be in a single mbuf?)

I think the EFBIG is replied by bus_dmamap_load_mbuf_sg(), but I
don't know if it can happen for an mbuf chain with < 32 entries?

I've cc'd Jack in case he knows, rick
ps: The other thing to try is setting rsize=32768,wsize=32768 options
    on the Linux client mounts. Either change should "fix" the long
    mbuf chain problem, but if one of these fixes the problem and
    the other one doesn't...??

> --
> John Baldwin
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