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RE: [Xen-devel][PATCH]Provide 3 times continously writes check and unshadow the guest page

  • To: "Tim Deegan" <Tim.Deegan@xxxxxxxxxx>
  • From: "Xin, Xiaohui" <xiaohui.xin@xxxxxxxxx>
  • Date: Fri, 25 Jan 2008 11:17:43 +0800
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 24 Jan 2008 19:18:41 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: Achebs8dQ6Vgy8fHTmOtRdXPSqmwFAAkae7w
  • Thread-topic: [Xen-devel][PATCH]Provide 3 times continously writes check and unshadow the guest page

>-----Original Message-----
>From: Tim Deegan [mailto:Tim.Deegan@xxxxxxxxxx]
>Sent: 2008年1月24日 17:49
>To: Xin, Xiaohui
>Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
>Subject: Re: [Xen-devel][PATCH]Provide 3 times continously writes check and
>unshadow the guest page
>At 10:19 +0800 on 24 Jan (1201169995), Xin, Xiaohui wrote:
>> >So to summarize, seven of your performance tests get slightly worse, two
>> >get slightly better and two (x64 linux kernel build times and iperf) get
>> >markedly better.  Do you have confidence intervals for the measurements,
>> >by the way?
>> >
>> Yes, we have confidence with the measurements, since it's always the
>> average number of 5 or 6 times.
>What I was asking for is some measurement of the variation among those 5
>or 6 times.  Ideally a metric of the statistical significance of the
>change, but at least some idea of whether I should take a ~1% change
>seriously.  For example, if a kernel build changes from 1m44s to 1m43s,
>that's maybe interesting if all 6 were exactly the same, but really not
>if there was about 10sec variation among them.
I have attached the original test result from our colleague who have done all 
the test, the performance data you have seen is concluded from it, just for 
your reference, and if you still have some other concerns or worries about the 
data, let us dig into it.

>> >Do your HVM linux guests have PV drivers?  If not, does using PV drivers
>> >make a difference to iperf?
>> >
>> No, the guests we used do not have PV drivers. What your concerns are
>> on this point?
>Just wondering whether using PV drivers results in better behaviour wrt
>shadowed data pages.
>> Then, how about your final opinion about the patch? We did not see it
>> clearly from your reply. :-(
>I'm undecided about it.  The measurements you gave look like it fixes
>one particularly bad case very well, but makes overall performance
>worse.  In that case, I'm wondering whether there might be a better way
>of fixing the network-buffer issue without degrading general
It fixed one bad case, and it improved the kernel build for ia32e Linux guest 
to 9.5%.

>Tim Deegan <Tim.Deegan@xxxxxxxxxx>
>Principal Software Engineer, Citrix Systems (R&D) Ltd.
>[Company #02300071, SL9 0DZ, UK.]

Attachment: 3_write_test_result.xls
Description: 3_write_test_result.xls

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