[Xen-bugs] [Bug 717] New: hdparm reports much slower cached I/O in dom0/domU than on native OS

[bugzilla-daemon@xxxxxxxxxxxxxxxxxxx]

http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=717

           Summary: hdparm reports much slower cached I/O in dom0/domU than
                    on native OS
           Product: Xen
           Version: unstable
          Platform: IA64
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P4
         Component: Hardware Support
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: ahs3@xxxxxxxxx


All comparisons (in the parentheses after the raw numbers) are
normalized to the "native" results; that is, a 1.0 result means
the domain ran at the same speed as native, a result < 1.0 means
the domain was slower, and a result > 1.0 means the domain was
faster.

o hdparm -tT /dev/sda2
     buffered IO: native 52.04 MB/s
                  dom0   48.10 (0.92)
                  domU   51.03 (0.98)

     cached IO:   native 2506.26 MB/s
                  dom0   1701.36 (0.68)
                  domU   1884.17 (0.75)

  comment: buffered IO does well, but why does cached fall off so much?

Configuration:
   HP zx6000 (aka rx2600 server, I believe)
   2-CPU (McKinley processor), 1GHz, 1499.13 bogomips each
   8 GB RAM

   Host: scsi0 Channel: 00 Id: 00 Lun: 00
     Vendor: HP 36.4G Model: MAN3367MC        Rev: HP05
     Type:   Direct-Access                    ANSI SCSI revision: 02
   Host: scsi0 Channel: 00 Id: 01 Lun: 00
     Vendor: HP 36.4G Model: ST336706LC       Rev: HP04
     Type:   Direct-Access                    ANSI SCSI revision: 02
   Host: scsi1 Channel: 00 Id: 02 Lun: 00
     Vendor: HP 36.4G Model: ST336706LC       Rev: HP04
     Type:   Direct-Access                    ANSI SCSI revision: 02

   Running Debian GNU/Linux (sid/unstable)
   Native: linux-image-2.6.17-1-mckinley-smp kernel
           init state 2, minimal daemons running

   Dom0: cset 10700, 2.6.16.13-xen kernel
         init state 2, minimal daemons running
         no domU's running

   DomU: cset 10700, 2.6.16.13-xen kernel
         init state 2, minimal daemons running
         this was the *only* domU running


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