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SubjectRe: [v2] PCI: Add an option to control probing of VFs before enabling SR-IOV
On Wed, Apr 12, 2017 at 09:37:22AM -0500, Bodong Wang wrote:
> On 4/11/2017 4:12 PM, Bjorn Helgaas wrote:
> >Hi Bodong,
> >
> >On Wed, Mar 22, 2017 at 05:53:58PM +0200, wrote:
> >>From: Bodong Wang <>
> >>
> >>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.
> >>
> >>Add a new PCI sysfs interface "sriov_probe_vfs" to control that
> >>from the 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
> >Is this basically the same functionality as /sys/bus/pci/drivers_autoprobe,
> >but limited to a specific PF? I.e., could we accomplish the same thing
> >with the following?
> >
> > # echo 0 > /sys/bus/pci/devices/DDDD:BB:dd.f/sriov_numvfs
> > # echo 0 > /sys/bus/pci/drivers_autoprobe
> > # echo 2 > /sys/bus/pci/devices/DDDD:BB:dd.f/sriov_numvfs
> > # echo 1 > /sys/bus/pci/drivers_autoprobe
> >
> >If not, can you contrast the above with drivers_autoprobe? If we need
> >both, should they be named more similarly?
> Hi Bjorn,
> I agree with Alex about not using driver_autoprobe to achieve this.
> It will affect all pci related device once it's disabled(probably in
> a bad way).

I agree drivers_autoprobe is racy with respect to other PCI devices, so
it's not a great solution to your issue. But I do want to make it
obvious that these are related concepts.

Alex mooted the idea of a generic driver core knob for devices that
create child devices. That's intriguing. What other situations
besides SR-IOV do this? Maybe we could add a "drivers_autoprobe"
inside the directory of each device that's capable of having child

If we continue with the current approach (instead of Alex's idea),
I propose that you:

- Name your new knob "sriov_drivers_autoprobe" to be consistent with
other sriov sysfs files while also being parallel to

- Update Documentation/ABI/testing/sysfs-bus-pci to document your
new knob

- Update Documentation/ABI/... to document drivers_autoprobe


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