Xen, Windows 2003 and APIC
 

Hi,

I've been investigating networking performance for Windows 2003 guests
on a Solaris dom0 and I've uncovered a couple of things which I don't
really understand and I'm looking for some explanations.

This first question is really directed at virtinst developers...

Windows guests have different ACPI and APIC settings depending on which
variant of Windows is to be installed:

variant: unspecified -> ACPI: true, APIC: true
variant: winxp -> ACPI: false, APIC: false
variant: win2k -> ACPI: false, APIC: false
variant: win2k3 -> ACPI: true, APIC: true
variant: vista -> ACPI: true, APIC: true

The question is: why don't all Windows variants have the same ACPI and APIC
settings?

The reason I'm curious, is that it seems like different combinations of
APIC and ACPI produce different functionality in the guest and different
levels of performance.

I did some tests with win2k3 guests and measured networking performance
using iperf.

I used the same dom0 system (snv_103) and created three W2K3 guests,
each with 1 CPU but different APIC and ACPI settings:

apic/acpi setting results (Mb/s throughput)
apic: 0 acpi: 0 834, 833
apic: 1 acpi: 1 718, 704
apic: 0 acpi: 1 872, 876

(higher numbers are better)

I only had time to perform two runs (the test is the iperf-2.0.2 1MB msg
test that I ran to microbenchmark TCP performance) for each guest,
but you can see that there is a fairly large and consistent (across two
runs for each guest) performance difference. It's about 20% faster when
apic is not specified for the guest.

My next question is: What is really happening when APIC is specified for
a windows guest and why does performance vary so much according to whether
it's specified or not?

Thanks for any help or insight anyone can offer.

Gary
--
Gary Pennington
Solaris Core OS
Sun Microsystems
Gary.Pennington@sun.com

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Xen, Windows 2003 and APIC
 

On Fri, Dec 05, 2008 at 04:42:57PM +0000, George Dunlap wrote:
> IIRC, only w2k3sp2+, vista, and w2k8 have lazy TPR. Not positive
> about w2k3sp1, but I think it doesn't. WinXP does not have lazy TPR
> in any service pack, AFAIK.
>
> What service pack of w2k3 did you do those tests with?
>

I'm not sure, because the ISO was provided by a colleague. I think it's
the original release of w2k3, with no service packs.

However, what I was mostly curious about was why specifying apic when the
guest was created made so much different to performance.

Gary

> Hopefully, sometime in the next few weeks, I'll be able to release my
> 'xenalyze' tool, which will help a lot with analyzing what's really
> going on with these kinds of workloads.
>
> -George
>
> On Fri, Dec 5, 2008 at 2:45 PM, Keir Fraser <keir.fraser@eu.citrix.com> wrote:
> > On 05/12/2008 14:03, "Gary Pennington" <Gary.Pennington@sun.com> wrote:
> >
> >> My next question is: What is really happening when APIC is specified for
> >> a windows guest and why does performance vary so much according to whether
> >> it's specified or not?
> >
> > Older Windows kernels update the APIC TPR a lot, and unless you have a very
> > modern Intel processor every one of those TPR updates causes a vmexit.
> >
> > Modern Windows (including possibly latest w2k3 service pack, but I'm not
> > totally certain) includes lazy TPR, which gets rid of the vast majority of
> > TPR updates, and hence will go much faster.
> >
> > -- Keir
> >
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xensource.com
> > http://lists.xensource.com/xen-devel
> >
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

--
Gary Pennington
Solaris Core OS
Sun Microsystems
Gary.Pennington@sun.com

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Xen, Windows 2003 and APIC
 

Gary Pennington wrote:
> Hi,
>
> I've been investigating networking performance for Windows 2003 guests
> on a Solaris dom0 and I've uncovered a couple of things which I don't
> really understand and I'm looking for some explanations.
>
> This first question is really directed at virtinst developers...
>
> Windows guests have different ACPI and APIC settings depending on which
> variant of Windows is to be installed:
>
> variant: unspecified -> ACPI: true, APIC: true
> variant: winxp -> ACPI: false, APIC: false
> variant: win2k -> ACPI: false, APIC: false
> variant: win2k3 -> ACPI: true, APIC: true
> variant: vista -> ACPI: true, APIC: true
>
> The question is: why don't all Windows variants have the same ACPI and APIC
> settings?
>
>

One of the motivations for the ACPI = False, was that when installing
those versions of windows with ACPI enabled, the installer required
manual intervention. The user had to hit F5 or something in a small
time frame and specify a non-default HAL, otherwise the install would
just freeze. Well, that's what I recall anyways. I can't seem to find
a bz about the issue, and the hg history isn't much help.

I have no idea if APIC played a part in the above issue, or why it's
off for winxp or win2000.

Thanks,
Cole

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