linux-kernel - RE: [PATCH 00/16] raid acceleration and asynchronous offload api for 2.6.22

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Date:	Thu, 10 May 2007 16:12:11 +0200
From:	Tomasz Chmielewski <mangoo@...g.org>
To:	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	rshitrit@...vell.com, dan.j.williams@...el.com,
	nickpiggin@...oo.com.au, Justin Piszcz <jpiszcz@...idpixels.com>,
	ilmari@...ari.org
Subject: RE: [PATCH 00/16] raid acceleration and asynchronous offload api
 for 2.6.22

Ronen Shitrit wrote:

> The resync numbers you sent, looks very promising :)
> Do you have any performance numbers that you can share for these set of
> patches, which shows the Rd/Wr IO bandwidth.

I have some simple tests made with hdparm, with the results I don't 
understand.

We see hdparm results are fine if we access the whole device:

thecus:~# hdparm -Tt /dev/sdd

/dev/sdd:
  Timing cached reads:   392 MB in  2.00 seconds = 195.71 MB/sec
  Timing buffered disk reads:  146 MB in  3.01 seconds =  48.47 MB/sec

But are 10 times worse (Timing buffered disk reads) when we access 
partitions:

thecus:/# hdparm -Tt /dev/sdc1 /dev/sdd1

/dev/sdc1:
  Timing cached reads:   396 MB in  2.01 seconds = 197.18 MB/sec
  Timing buffered disk reads:   16 MB in  3.32 seconds =   4.83 MB/sec

/dev/sdd1:
  Timing cached reads:   394 MB in  2.00 seconds = 196.89 MB/sec
  Timing buffered disk reads:   16 MB in  3.13 seconds =   5.11 MB/sec

Why is it so much worse?

I used 2.6.21-iop1 patches from http://sf.net/projects/xscaleiop; right 
now I use 2.6.17-iop1, for which the results are ~35 MB/s when accessing 
a device (/dev/sdd) or a partition (/dev/sdd1).

In kernel config, I enabled Intel DMA engines.

The device I use is Thecus n4100, it is "Platform: IQ31244 (XScale)", 
and has 600 MHz CPU.

-- 
Tomasz Chmielewski
http://wpkg.org

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