Re: [Xen-devel] Device Reset on Nvidia GPUs

[Gordan Bobic <gordan@xxxxxxxxxx>]

On Fri, 15 Nov 2013 09:40:04 -0500, Konrad Rzeszutek Wilk 
<konrad.wilk@xxxxxxxxxx> wrote:
> On Fri, Nov 15, 2013 at 02:29:39PM +0000, Gordan Bobic wrote:
> > On Fri, 15 Nov 2013 14:27:21 +0000, Stefano Stabellini
> > <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> > >On Fri, 15 Nov 2013, Gordan Bobic wrote:
> > >>I've noticed that nouveau driver has a sysfs reset implemented
> > >>(although I'm not sure whether it is just a stub or whether it
> > >>does anything).
> > >>
> > >>Now, I fully understand that this is not actually necessary,
> > >>based purely on empirical evidence:
> > >>
> > >>My ATI cards reliably crash the host when the domU the are passed
> > >>to is rebooted, and the xen-pciback driver does have the sysfs
> > >>reset implemented for ATI cards.
> > >>
> > >>OTOH, my (modified) Nvidia cards handle domU reboots perfectly
> > >>and the xen-pciback driver has no sysfs reset implementation
> > >>for those.
> > >>
> > >>So I'm kind of torn between:
> > >>1) It's not broken so don't even think about trying to fix it.
> > >>2) Since FOSS reset implementation seems to exist, it might be
> > >>handy to port it into the xen-pciback feature list (caveat:
> > >>this may impact 1), which would be embarrasing).
> > >>
> > >>Thoughts?
> > >
> > >libxl is capable of using the sysfs reset node, so there shouldn't 
> > be
> > >any needed for porting the reset code to pciback
> >
> > Not quite - when the device is owned by xen-pciback, there is
> > no reset node. When it is owned by nouveau, the reset node in
> > sysfs is there.
> Sure, but pciback does the reset:
>
>
>       /* We need the device active to save the state. */
>
>         dev_dbg(&dev->dev, "save state of device\n");
>
>         pci_save_state(dev);
>
>         dev_data->pci_saved_state = pci_store_saved_state(dev);
>
>         if (!dev_data->pci_saved_state)
>
>                 dev_err(&dev->dev, "Could not store PCI conf saved
> state!\n");
>         else {
>
>                 dev_dbg(&dev->dev, "resetting (FLR, D3, etc) the
> device\n");
>                 __pci_reset_function_locked(dev);
>
>                 pci_restore_state(dev);
>
>         }
>
> The pci_reset_function(..) - the non-locked variant) is called when 
> you
> do 'reset' to the SysFS.
>
> Unless the nouveau driver does some extra 'reset'?
I don't know for sure at the moment. I was just basing this on the
observation that xl complains that there is no sysfs reset for the
device when instantiating the VM and there being no reset node for
the device in sysfs.

It seems oddly inconsistent that there is a reset node in sysfs for
ATI cards (that crash the host on domU reboot) but no reset node for
Nvidia cards (which work fine on domU reboot).

There is no FLR or D3 PM on my Nvidia cards, so that could
be why (there is D3hot on ATI). But nouveau driver still exposes
a reset node for the device.

Gordan

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