Date:	Thu, 12 Jul 2012 08:53:03 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Michael Tokarev <mjt@....msk.ru>
Cc:	"Myklebust, Trond" <Trond.Myklebust@...app.com>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	Linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: 3.0+ NFS issues

On Tue, Jul 10, 2012 at 04:52:03PM +0400, Michael Tokarev wrote:
> I tried to debug this again, maybe to reproduce in a virtual machine,
> and found out that it is only 32bit server code shows this issue:
> after updating the kernel on the server to 64bit (the same version)
> I can't reproduce this issue anymore.  Rebooting back to 32bit,
> and voila, it is here again.
> 
> Something apparenlty isn't right on 32bits... ;)
> 
> (And yes, the prob is still present and is very annoying :)

OK, that's very useful, thanks.  So probably a bug got introduced in the
32-bit case between 2.6.32 and 3.0.

My personal upstream testing is normally all x86_64 only.  I'll kick off
a 32-bit install and see if I can reproduce this quickly.

Let me know if you're able to narrow this down any more.

--b.

> 
> Thanks,
> 
> /mjt
> 
> 
> On 31.05.2012 17:51, Michael Tokarev wrote:
> > On 31.05.2012 17:46, Myklebust, Trond wrote:
> >> On Thu, 2012-05-31 at 17:24 +0400, Michael Tokarev wrote:
> > []
> >>> I started tcpdump:
> >>>
> >>>  tcpdump -npvi br0 -s 0 host 192.168.88.4 and \( proto ICMP or port 2049 \) -w nfsdump
> >>>
> >>> on the client (192.168.88.2).  Next I mounted a directory on the client,
> >>> and started reading (tar'ing) a directory into /dev/null.  It captured a
> >>> few stalls.  Tcpdump shows number of packets it got, the stalls are at
> >>> packet counts 58090, 97069 and 97071.  I cancelled the capture after that.
> >>>
> >>> The resulting file is available at http://www.corpit.ru/mjt/tmp/nfsdump.xz ,
> >>> it is 220Mb uncompressed and 1.3Mb compressed.  The source files are
> >>> 10 files of 1Gb each, all made by using `truncate' utility, so does not
> >>> take place on disk at all.  This also makes it obvious that the issue
> >>> does not depend on the speed of disk on the server (since in this case,
> >>> the server disk isn't even in use).
> >>
> >> OK. So from the above file it looks as if the traffic is mainly READ
> >> requests.
> > 
> > The issue here happens only with reads.
> > 
> >> In 2 places the server stops responding. In both cases, the client seems
> >> to be sending a single TCP frame containing several COMPOUNDS containing
> >> READ requests (which should be legal) just prior to the hang. When the
> >> server doesn't respond, the client pings it with a RENEW, before it ends
> >> up severing the TCP connection and then retransmitting.
> > 
> > And sometimes -- speaking only from the behavour I've seen, not from the
> > actual frames sent -- server does not respond to the RENEW too, in which
> > case the client reports "nfs server no responding", and on the next
> > renew it may actually respond.  This happens too, but much more rare.
> > 
> > During these stalls, ie, when there's no network activity at all,
> > the server NFSD threads are busy eating all available CPU.
> > 
> > What does it all tell us? :)
> > 
> > Thank you!
> > 
> > /mjt
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