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RE: [Xen-devel] IRQ SMP affinity problems in domU with vcpus > 4 on HP ProLiant G6 with dual Xeon 5540 (Nehalem)

Thanks for the suggestions Qing. I will send you the log with "hvm_debug=0x200" 
and try Xen 3.5 unstable.


-----Original Message-----
From: Qing He [mailto:qing.he@xxxxxxxxx] 
Sent: Friday, October 09, 2009 2:08 AM
To: Keir Fraser
Cc: Cinco, Dante; xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] IRQ SMP affinity problems in domU with vcpus > 4 on HP 
ProLiant G6 with dual Xeon 5540 (Nehalem)

On Fri, 2009-10-09 at 05:35 +0800, Keir Fraser wrote:
> On 08/10/2009 19:11, "Cinco, Dante" <Dante.Cinco@xxxxxxx> wrote:
> > The IRQ SMP affinity problem happens on just the passthrough one using MSI.
> > 
> > I've only used Xen 3.4.1. Are you aware of recent code changes that 
> > may address this issue?
> No, but it might be worth a try. Unfortunately I'm not so familiar 
> with the MSI passthru code as I am with the rest of the irq emulation 
> layer. Qing He
> (cc'ed) may be able to assist, as I think he did much of the 
> development of MSI support for passthru devices.

MSI passthru uses emulation, there is nothing to do between the guest affinity 
and the physical affinity. When an MSI is received, a vmsi logic calculates the 
destination and sets the virtual local APIC of that VCPU.

But after checking the code, the part handling DM=0 is there and I haven't 
found big problems on the first glance, maybe there is some glitch that causes 
the MSI failure in physical mode.

Some debug log can be helpful to track down the problem. Can you add 
'hvm_debug=0x200' to the xen command line and post the xm dmesg result?
This will print hvm debug level DBG_LEVEL_IOAPIC which includes vmsi delivery 

There are two patches between 3.4.1 and unstable (20084, 20140), these are 
mainly cleanup patches but the related code does change, don't know if they fix 
this issue.


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