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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>
Subject: Re: [PATCH] readahead:add blk_run_backing_dev
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> >> >even consumed 9% of a CPU, so where on earth has the kernel gone to?
> >> >
> >> >Have you been able to reproduce this in your testing?
> >> 
> >> Yes, this test on my environment is reproducible.
> >
> >Hisashi, does your environment have some special configurations?
> 
> Hi.
> My testing environment is as follows:
> Hardware: HP DL580 
> CPU:Xeon 3.2GHz *4 HT enabled
> Memory:8GB
> Storage: Dothill SANNet2 FC (7Disks RAID-0 Array)
> 
> I did dd to this disk-array and got improved performance number.
> 
> I noticed that when a disk is just one HDD, performance improvement
> is very small.

thas's odd.

Why your patch depend on transfer rate difference?