linux-kernel - Re: Massive slowdown when re-querying large nfs dir

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Message-ID: <18225.26935.146395.366451@notabene.brown>
Date:	Wed, 7 Nov 2007 18:28:55 +1100
From:	Neil Brown <neilb@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Al Boldi <a1426z@...ab.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Massive slowdown when re-querying large nfs dir

On Tuesday November 6, akpm@...ux-foundation.org wrote:
> > On Tue, 6 Nov 2007 14:28:11 +0300 Al Boldi <a1426z@...ab.com> wrote:
> > Al Boldi wrote:
> > > There is a massive (3-18x) slowdown when re-querying a large nfs dir (2k+
> > > entries) using a simple ls -l.
> > >
> > > On 2.6.23 client and server running userland rpc.nfs.V2:
> > > first  try: time -p ls -l <2k+ entry dir>  in ~2.5sec
> > > more tries: time -p ls -l <2k+ entry dir>  in ~8sec
> > >
> > > first  try: time -p ls -l <5k+ entry dir>  in ~9sec
> > > more tries: time -p ls -l <5k+ entry dir>  in ~180sec
> > >
> > > On 2.6.23 client and 2.4.31 server running userland rpc.nfs.V2:
> > > first  try: time -p ls -l <2k+ entry dir>  in ~2.5sec
> > > more tries: time -p ls -l <2k+ entry dir>  in ~7sec
> > >
> > > first  try: time -p ls -l <5k+ entry dir>  in ~8sec
> > > more tries: time -p ls -l <5k+ entry dir>  in ~43sec
> > >
> > > Remounting the nfs-dir on the client resets the problem.
> > >
> > > Any ideas?
> > 
> > Ok, I played some more with this, and it turns out that nfsV3 is a lot 
> > faster.  But, this does not explain why the 2.4.31 kernel is still over 
> > 4-times faster than 2.6.23.
> > 
> > Can anybody explain what's going on?
> > 
> 
> Sure, Neil can! ;)

Nuh.
He said "userland rpc.nfs.Vx".  I only do "kernel-land NFS".  In these
days of high specialisation, each line of code is owned by a different
person, and finding the right person is hard....

I would suggest getting a 'tcpdump -s0' trace and seeing (with
wireshark) what is different between the various cases.

NeilBrown
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