Re: [Xen-devel] Xen-unstable: pci-passthrough regression bisected to: x86/smp: use APIC ALLBUT destination shorthand when possible

[Jan Beulich <jbeulich@xxxxxxxx>]

On 03.02.2020 13:41, Roger Pau Monné wrote:
> On Mon, Feb 03, 2020 at 01:30:55PM +0100, Sander Eikelenboom wrote:
>> On 03/02/2020 13:23, Roger Pau Monné wrote:
>>> On Mon, Feb 03, 2020 at 09:33:51AM +0100, Sander Eikelenboom wrote:
>>>> Hi Roger,
>>>>
>>>> Last week I encountered an issue with the PCI-passthrough of a USB 
>>>> controller. 
>>>> In the guest I get:
>>>>     [ 1143.313756] xhci_hcd 0000:00:05.0: xHCI host not responding to stop 
>>>> endpoint command.
>>>>     [ 1143.334825] xhci_hcd 0000:00:05.0: xHCI host controller not 
>>>> responding, assume dead
>>>>     [ 1143.347364] xhci_hcd 0000:00:05.0: HC died; cleaning up
>>>>     [ 1143.356407] usb 1-2: USB disconnect, device number 2
>>>>
>>>> Bisection turned up as the culprit: 
>>>>    commit 5500d265a2a8fa63d60c08beb549de8ec82ff7a5
>>>>    x86/smp: use APIC ALLBUT destination shorthand when possible
>>>
>>> Sorry to hear that, let see if we can figure out what's wrong.
>>
>> No problem, that is why I test stuff :)
>>
>>>> I verified by reverting that commit and now it works fine again.
>>>
>>> Does the same controller work fine when used in dom0?
>>
>> Will test that, but as all other pci devices in dom0 work fine,
>> I assume this controller would also work fine in dom0 (as it has also
>> worked fine for ages with PCI-passthrough to that guest and still works
>> fine when reverting the referenced commit).
> 
> Is this the only device that fails to work when doing pci-passthrough,
> or other devices also don't work with the mentioned change applied?
> 
> Have you tested on other boxes?
> 
>> I don't know if your change can somehow have a side effect
>> on latency around the processing of pci-passthrough ?
> 
> Hm, the mentioned commit should speed up broadcast IPIs, but I don't
> see how it could slow down other interrupts. Also I would think the
> domain is not receiving interrupts from the device, rather than
> interrupts being slow.
> 
> Can you also paste the output of lspci -v for that xHCI device from
> dom0?

If this is AMD hardware, then another thing to try just to get an
additional data point would be limiting of CPUs used ("maxcpus="),
as that ought to suppress the actual sending of ALLBUT IPIs.

Jan

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