Re: [Xen-users] xhci_hcd intterrupt affinity in Dom0/DomU limited to single interrupt

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Sat, 2015-08-15 at 14:31 +0000, Justin Acker wrote:
> Hello,
> 
> Is there a configuration option or patch to control the xhci_hcd 
> interrupt smp affinity? It looks like the Dom0 and DomU, if passed 
> through, will only use a single interrupt on the xhci_hcd controller 
> (usually the first unless smp affinity is manually set).

>  The xhci_hcd interrupts appear to be scheduled across all CPUs when 
> booting with a native kernel. I've noticed other devices seem to schedule 
> interrupts across all CPUs when in the Dom0 and DomU.

This suggests that you do have irqbalanced running and it is doing stuff,
the interrupt counts you showed suggest it is rebalancing some stuff

Perhaps irqbalanced has just decided that xchi_hcd should be on CPU0? After
all something should run there...

The proc file is cumulative, meaning that while multiple CPUs may have a
non-zero count for a given interrupt not all of them will be incrementing
right now. So I'm not completely sure that what you are seeing isn't just
normal behaviour.

I'm not sure if Xen pirqs support delivery to a set of CPUs rather than
just a single one at a time, TBH I'm not even really sure what the
behaviour of MSIs for the native case is.

Devices which want to benefit from multiple CPUs typically need to have
multiple queues and multiple associated interrupts.

Sorry, there's a lot more "not sure"s in there than I would like...

Ian.

>  Using Xen 4.5 and Kernel 3.19. 
> 
>  76:      11304          0     149579          0          0          0   
>        0          0  xen-pirq-msi       0000:00:1f.2
>  77:       1243          0          0      35447          0          0   
>        0          0  xen-pirq-msi       radeon
>  78:      82521          0          0          0          0          0   
>        0          0  xen-pirq-msi       xhci_hcd
>  79:         23          0          0          0          0          0   
>        0          0  xen-pirq-msi       mei_me
>  80:         11          0          0          0          0        741   
>        0          0  xen-pirq-msi       em1
>  81:        350          0          0          0       1671          0   
>        0          0  xen-pirq-msi       iwlwifi
>  82:        275          0          0          0          0          0   
>        0          0  xen-pirq-msi       snd_hda_intel
> 
> 
> 
> The USB controller is an Intel C210:
> 
> 00:14.0 USB controller: Intel Corporation 7 Series/C210 Series Chipset 
> Family USB xHCI Host Controller (rev 04) (prog-if 30 [XHCI])
>     Subsystem: Dell Device 053e
>     Flags: bus master, medium devsel, latency 0, IRQ 78
>     Memory at f7f20000 (64-bit, non-prefetchable) [size=64K]
>     Capabilities: [70] Power Management version 2
>     Capabilities: [80] MSI: Enable+ Count=1/8 Maskable- 64bit+
>     Kernel driver in use: xhci_hcd
>     Kernel modules: xhci_pci
> 
> 
> 
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