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Date:	Thu, 27 Dec 2007 10:07:38 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	saeed bishara <saeed.bishara@...il.com>
CC:	linux-kernel@...r.kernel.org, NFS list <linux-nfs@...r.kernel.org>
Subject: Re: read-ahead in NFS server

saeed bishara wrote:
>>>> Are you using TCP?  Are you using NFSv4, or an older version?
>>> I'm using NFSv3/UDP.
>> IMO, you definitely want TCP and NFSv4.  Much better network behavior,
>> with some of the silly UDP limits (plus greatly improved caching
>> behavior, due to v4 delegations).
> the clients of my system going to be embedded system with low
> performance cpus and I need UDP as it needs less cpu power.

I bet
	TCP + fewer revalidations + greater local pagecache activity
uses less cpu power than
	UDP + revalidations + rx/tx network activity


>>> when I run local dd with bs=4K, I can see that the average IO size is
>>> more than 300KB.
>> Read-ahead is easier in NFSv4, because the client probably has the file
>> delegated locally, and has far less need to constantly revalidate file
>> mapping(s).
> I'll check that.
> but what about the server side? why the issued IO's are only as twice
> as the size of the NFS requests?

No idea.  I bet the source code can tell you :)

	Jeff


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