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

[Tim Deegan <Tim.Deegan@xxxxxxxxxx>]

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.

> >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
performance.

Cheers,

Tim.

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

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