RE: [Xen-users] Xen GPL PV and undesirable requirement for APIC (irq >15)

["Nick Couchman" <Nick.Couchman@xxxxxxxxx>]

I certainly saw the issue with the non-APIC HAL, but I don't see any performance or CPU issues with the APIC MP HAL.

-Nick


-----Original Message-----
From: Venefax <venefax@xxxxxxxxx>
To: 'James Harper' <james.harper@xxxxxxxxxxxxxxxx>, 'Oliver Wilcock' <oliver@xxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] Xen GPL PV and undesirable requirement for APIC (irq	>15)
Date: Tue, 25 Nov 2008 10:03:48 -0500

I concur on seeing the issue. I changed the HAL to Standard PC (Non-apic)
and the Xennet driver strangely got an IP address from the DHCP, but could
not communicate after that. The regular APIC Multiprocessor HAL works fine
with the drivers, but a few machines kill the server. In fact, the idle
usage is 0.9% and if you add more virtual cpus it shoots up to 3.5%, making
impossible to use.
Looking at in perspective, if we are forced to use a single VCPU windows
machine, then Virtual Box gives a substantial advantage in performance, and
you may run many more machines. They don't support SMP, but it seems that
XEN does not either.
 

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of James Harper
Sent: Tuesday, November 25, 2008 4:18 AM
To: Oliver Wilcock; xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] Xen GPL PV and undesirable requirement for APIC
(irq >15)

> Hi James,
> 
> Thanks for all the hard work on the GPL PV project.
> 
> I've been having trouble with the more recent builds and then saw
this:
> 
> > Making Windows do the right thing with IRQ's etc was really hard, I
> tried quite a few different approaches and this was the best one I
could
> come up with. It is a pity that it doesn't work with apic=0, but I
don't
> think that there is a valid reason these days why you would set
apic=0.
> Previously (xen 3.0.x) it was required to make some versions of
windows
> work.
> >
> > James
> 
> The APIC problems haven't gone away, as far as I'm aware...
> 
> 
> Like a number of people I run my Windows HVMs with apic=0 (or rather
with
> the "Standard PC" hal.dll or halacpi.dll) to avoid performance
problems.
> 
> Earlier releases of the GPL PV drivers worked well with "Standard PC"
and
> Windows XP halacpi.dll , but in the last few weeks they have been
> unusable.
> 
> I just wanted to express my concern about the idea that the xennet
driver
> should crash if used with a non APIC HAL.  The xennet driver should
work
> with any HAL, just like the xenvbd driver.
> 
> It would be nice if the apic problems were fixed, too.  Any idea why
the
> APIC related problem?  I think the pre-requisites for the symptoms are
AMD
> CPU and 64 bit hypervisor and 32 bit Windows HVM.
> 
> reference:
> http://forums.novell.com/novell-product-support-forums/suse-linux-
> enterprise-server-sles/sles-virtualization/337603-win2k3-xp-poor-
> performance-eats-10-cpu-while-idle.html

I reversed the bit that made it fail when it couldn't find an IRQ > 16.
I had incorrectly assumed that all IRQ's < 16 were ISA anyway. I think I
just need to detect the type of IRQ (ISA or PCI) and act
appropriately...

I will revisit this when I've gotten the pvscsi working again (I
desperately need that for internal testing, but it involves quite a few
changes).

James

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