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[Xen-devel] Timer Frequency Problem

  • To: <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "jowkju" <jowkju@xxxxxxxxxxxxx>
  • Date: Wed, 7 Nov 2007 17:02:26 +0900
  • Delivery-date: Mon, 19 Nov 2007 10:17:43 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcghFIjiqwPEhJMaSnmPqn69NrExMA==

Hello, Xen Users~!!


I installed xenserver-3.2.0 on my dell system. When I created a RHEL-4.4 guest OS(2.6.9 kernel) on it,

xen patch changed the timer frequency HZ to be 100 instead of 1000. And I found the dom0 kernel

also uses a 100HZ instead of 1000HZ.


The general kernel or xen kernel both use USER_HZ as 100HZ, so I guess, for the applications running mainly in

the user address space, the performance will be simillar. However, some applications running mainly

in the kernel address space, the performance will be a lot affected by the differences in HZ between general kernel and

xen kernel.


My questions are

01.   Why do the xen patches for the dom0 and domU force to use 100HZ instead of 1000HZ for the timer frequency?


02.   I experienced more significant performance overhead in 2D graphic operations when I used 100HZ frequency instead of
1000HZ than any other applications such as heavy network IO or disk IO workload. Could someone have an idea on that?



Thank you!

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