Re: [PATCH] pci/sriov: Add an option to probe VFs or not before enabling SR-IOV

[Bodong Wang]

On 3/20/2017 7:24 PM, Gavin Shan wrote:
> On Mon, Mar 20, 2017 at 06:34:23PM -0500, Bodong Wang wrote:
> > On 3/20/2017 6:07 PM, Gavin Shan wrote:
> > > On Mon, Mar 20, 2017 at 05:14:34PM +0200, bodong@xxxxxxxxxxxx wrote:
> > > > From: Bodong Wang <bodong@xxxxxxxxxxxx>
> > > >
> > > > Sometimes it is not desirable to probe the virtual functions after
> > > > SRIOV is enabled. This can save host side resource usage by VF
> > > > instances which would be eventually probed to VMs.
> > > >
> > > > Added a new PCI sysfs interface "sriov_probe_vfs" to control that
> > > >from PF, all current callers still retain the same functionality.
> > > > To modify it, echo 0/n/N (disable probe) or 1/y/Y (enable probe) to
> > > >
> > > > /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_probe_vfs
> > > >
> > > > Note that, the choice must be made before enabling VFs. The change
> > > > will not take effect if VFs are already enabled. Simply, one can set
> > > > sriov_numvfs to 0, choose whether to probe or not, and then resume
> > > > sriov_numvfs.
> > > Bodong, I'm not sure if there is a requirement to load driver for the
> > > specified number of VFs? That indicates no driver will be loaded for
> > > other VFs. If so, this interface might serve the purpose as well.
> > Gavin, thanks for the review. That is indeed an interesting suggestion.
> > Theoretically,  we can change that probe_vfs from boolean to integer. And use
> > it as a counter to probe the first N VFs(if N < total_vfs).  Let's see if
> > there are any objections.
> Ok.
>
> > > +#ifdef CONFIG_PCI_IOV
> > > +	if (!pci_dev->is_virtfn ||
> > > +	    (pci_dev->is_virtfn && pci_dev->physfn->sriov->probe_vfs)) {
> > > +#endif
> > > +		error = __pci_device_probe(drv, pci_dev);
> > > +		if (error) {
> > > +			pcibios_free_irq(pci_dev);
> > > +			pci_dev_put(pci_dev);
> > > +		}
> > > +#ifdef CONFIG_PCI_IOV
> > > 	}
> > > +#endif
> > >
> > > I think it's reasonable to have a inline function for this check:
> > It's doable, but what's the benefit?
> > > #ifdef CONFIG_PCI_IOV
> > > static inline bool pci_device_can_probe(struct pci_dev *pdev)
> > > {
> > > 	return (!pdev->is_virtfn || pdev->physfn->sriov->probe_vfs);
> > should be return (!pdev->is_virtfn || (pci_dev->is_virtfn &&
> > pci_dev->physfn->sriov->probe_vfs));
> >
> > We want to probe that device if 1) it's a PF 2) it'a VF and probe_vfs is set
> > > }
> > > #else
> > > static inline bool pci_device_can_probe(struct pci_dev *pdev)
> > > {
> > > 	return true;
> > > }
> > This function will be a waste if CONFIG_PCI_IOV is not defined.
> > > #endif
> It makes the code a bit clean. Nope, the proposed conditional
> expression is elaborate. Yeah, the purpose is exactly same as
> you said: probe driver for non-VF or VFs that were allowed.
>
>       (!pdev->is_virtfn || pdev->physfn->sriov->probe_vfs);
>
> When pdev->is_virtfn is flase, "pdev->physfn->sriov->probe_vfs"
> doesn't take effect. Otherwise, it means pdev->is_virtfn is true
> indirectly and going to check "pdev->physfn->sriov->probe_vfs".
> So it needn't check pdev->is_virtfn explicitly in later case,
> but it isn't wrong :)
>
> Thanks,
> Gavin
Make sense :) Will apply in V1.

Thanks,

Bodong