Xen users - May 2007 - hdparm strange behaviour on centos 5.0 using the latest kernel

After booting into Linux 2.6.18-8.1.3.el5xen

#> hdparm -tT /dev/sda
/dev/sda:
 Timing cached reads:   10512 MB in  1.98 seconds = 5306.82 MB/sec
 Timing buffered disk reads:  210 MB in  3.02 seconds =  69.58 MB/sec

Then I start a domu with the command:
#>xm create <domainname>
This domain uses file based Virtual block devices.

And now the hard drive performance goes down dramatically in domain 0.
#> hdparm -tT /dev/sda
/dev/sda:
 Timing cached reads:   384 MB in  2.00 seconds = 192.08 MB/sec
 Timing buffered disk reads:  130 MB in  3.03 seconds =  42.93 MB/sec

The performance of domu is also very bad:

#>hdparm -tT /dev/xvda3

/dev/xvda3:
 Timing cached reads:    72 MB in  2.08 seconds =  34.66 MB/sec
 Timing buffered disk reads:   14 MB in  3.27 seconds =   4.28 MB/sec

Any idea how to trouble shoot this ?

-- 
Vikas

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