Re: [Xen-devel] Re: Still struggling with HVM: tx timeouts on emulated nics

[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

On 21.09.2011 15:31, Stefano Stabellini wrote:
> On Wed, 21 Sep 2011, Stefan Bader wrote:
>> This is on 3.0.4 based dom0 and domU with 4.1.1 hypervisor. I tried using the
>> default 8139cp and ne2k_pci emulated nic. The 8139cp one at least comes up 
>> and
>> gets configured via dhcp. And initial pings also get routed and done 
>> correctly.
>> But slightly higher traffic (like checking for updates) hangs. And after a 
>> while
>> there are messages about tx timeouts.
>> The ne2k_pci type nic almost immediately has those issues and never comes up
>> correctly.
>>
>> I am attaching the dmesg of the guest with apic=debug enabled. I am not sure 
>> how
>> this should be but both nics get configured with level,low IRQs. Disk 
>> emulation
>> seems to be ok but that seem to use IO-APIC-edge. And any other IRQs seem to 
>> be
>> at least not level.
> 

> Does the e1000 emulated card work correctly?

Yes, that one seems to work ok.

> What happens if you disable interrupt remapping (see patch below)?

8139cp seems to work correctly now (much higher irq stats as well) and e1000
still works. Both then using IOAPIC-fasteoi.

> 
> 
> diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
> index 1017c7b..472a58b 100644
> --- a/arch/x86/pci/xen.c
> +++ b/arch/x86/pci/xen.c
> @@ -354,8 +354,7 @@ int __init pci_xen_init(void)
>  
>  int __init pci_xen_hvm_init(void)
>  {
> -     if (!xen_feature(XENFEAT_hvm_pirqs))
> -             return 0;
> +     return 0;
>  
>  #ifdef CONFIG_ACPI
>       /*
> 
> 
>> Btw, what exactly is the difference between xen-pirq-ioapic and IO-APIC?
> 
> xen-pirq-ioapic interrupts are interrupts that have been remapped onto
> event channels

Ah ok, thanks.

> 
> 
>> Another problem came up recently though that may just be me doing the wrong
>> thing. Normally I boot with xen_emul_unplug=unnecessary as I want the 
>> emulated
>> devices. xen-blkfront is a module in my case and I thought I once had been 
>> able
>> to use that by removing the unplug arg and making the blkfront driver load. 
>> But
>> when I recently tried the module loaded but no disks appeared... Again, not 
>> sure
>> I just forgot how to do that right or that was different when using a 4.1.0
>> hypervisor still...
>  
> xen_emul_unplug=unnecessary allows the kernel to use PV interfaces on
> older hypervisors that didn't support the unplug protocol and had other
> ways to cope with multiple drivers accessing the same devices.
> You can use xen_emul_unplug=never to prevent any unplug but you won't
> get any PV interfaces.

Hm, odd. Somehow I thought that I had been using pv interfaces that way when the
interrupts for the emulated ide was broken.
A bit suboptimal atm, because without any option and a kernel compiled with the
platform pci and pv drivers (as modules) booting in HVM mode the kernel decides
that having both is no use and unplugs the emulated devices. Which then leaves
you with ... none.

-Stefan
> 
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