linux-kernel - Re: [RFC] nfs: use 4*rsize readahead size

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Message-ID: <1267539563.3099.43.camel@localhost.localdomain>
Date:	Tue, 02 Mar 2010 09:19:23 -0500
From:	Trond Myklebust <Trond.Myklebust@...app.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Dave Chinner <david@...morbit.com>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] nfs: use 4*rsize readahead size

On Tue, 2010-03-02 at 11:10 +0800, Wu Fengguang wrote: 
> Dave,
> 
> Here is one more test on a big ext4 disk file:
> 
> 	   16k	39.7 MB/s
> 	   32k	54.3 MB/s
> 	   64k	63.6 MB/s
> 	  128k	72.6 MB/s
> 	  256k	71.7 MB/s
> rsize ==> 512k  71.7 MB/s
> 	 1024k	72.2 MB/s
> 	 2048k	71.0 MB/s
> 	 4096k	73.0 MB/s
> 	 8192k	74.3 MB/s
> 	16384k	74.5 MB/s
> 
> It shows that >=128k client side readahead is enough for single disk
> case :) As for RAID configurations, I guess big server side readahead
> should be enough.

There are lots of people who would like to use NFS on their company WAN,
where you typically have high bandwidths (up to 10GigE), but often a
high latency too (due to geographical dispersion).
My ping latency from here to a typical server in NetApp's Bangalore
office is ~ 312ms. I read your test results with 10ms delays, but have
you tested with higher than that?

Cheers
  Trond
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