From: Krishna Kumar2 <krkumar2@in.ibm.com>
Subject: Re: NFS performance degradation of local loopback FS.
Date: Fri, 20 Jun 2008 12:09:11 +0530
Message-ID: <OF5312A09D.CAC110C0-ON6525746E.00245BF4-6525746E.00248C25@in.ibm.com>
References: <485A569A.8060601@panasas.com>
Mime-Version: 1.0
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Cc: linux-nfs@vger.kernel.org, Peter Staubach <staubach@redhat.com>
To: Benny Halevy <bhalevy@panasas.com>
In-Reply-To: <485A569A.8060601@panasas.com>
Sender: linux-nfs-owner@vger.kernel.org

Thanks Peter for your explanation, and Benny for this option I was not
aware of. Let me
run some tests with this option.

Regards,

- KK

linux-nfs-owner@vger.kernel.org wrote on 06/19/2008 06:22:42 PM:

> On Jun. 19, 2008, 15:04 +0300, Peter Staubach <staubach@redhat.com>
wrote:
> > Krishna Kumar2 wrote:
> >>>       200 processes:
> >>>
> >> By "200 processes", I meant 200 dd's, each reading from /dev/zero and
> >> writing to a file on the filesystem. The script "nfs" was run twice,
first
> >> with
> >> a local filesystem and the second time with the same filesystem NFS
> >> mounted.
> >>
> >>
> >
> > Well, you aren't exactly comparing apples to apples.  The NFS
> > client does close-to-open semantics, meaning that it writes
> > all modified data to the server on close.  The dd commands run
> > on the local file system do not.  You might trying using
> > something which does an fsync before closing so that you are
> > making a closer comparison.
>
> try dd conv=fsync ...
>
> Benny
>
> >
> > All that said, yes, one would expect a slow down.  How much is
> > debatable and varies from platform to platform and load to load.
> >
> > I would also advise care when running NFS like that.  It is
> > subject to deadlock and is not recommended.
> >
> >        ps
> >
> >> Thanks,
> >>
> >> - KK
> >>
> >> linux-nfs-owner@vger.kernel.org wrote on 06/19/2008 12:16:23 PM:
> >>
> >>
> >>> Hi,
> >>>
> >>> I am running 2.6.25 kernel on a [4 way, 3.2 x86_64, 4GB] system. The
test
> >>> is doing I/O on a local ext3 filesystem, and measuring the bandwidth,
and
> >>> then NFS mounting the filesystem loopback on the same system. I have
> >>> configured 64 nfsd's to run. The test script is attached at the
bottom.
> >>>
> >>> My configuration is:
> >>>       /dev/some-local-disk  :            /local
> >>>       NFS mount /local       :            /nfs
> >>>
> >>> The result is:
> >>>       200 processes:
> >>>             /local: 108000 KB/s
> >>>             /nfs:     66000 KB/s: Drop of 40%
> >>>
> >>>       300 processes (KB/s):
> >>>             /local: 112000 KB/s
> >>>             /nfs:    57000 KB/s: Drop of 50%
> >>>
> >>> I am not using any tuning, though I have tested with both
> >>> sunrpc.tcp_slot_table_entries=16 & 128
> >>>
> >>> Is this big a drop expected for a loopback NFS mount? Any
> >>> feedback/suggestions are very
> >>> appreciated.
> >>>
> >>> Thanks,
> >>>
> >>> - KK
> >>>
> >>> (See attached file: nfs)[attachment "nfs" deleted by Krishna
> >>>
> >> Kumar2/India/IBM]
> >>
> >> --
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> >>
> >
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>
> --
> Benny Halevy
> Software Architect
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>
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