linux-kernel - Re: [v2] PCI: Add an option to control probing of VFs before enabling SR-IOV

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Date:   Wed, 12 Apr 2017 11:00:06 -0500
From:   Bodong Wang <bodong@...lanox.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
CC:     <bhelgaas@...gle.com>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <saeedm@...lanox.com>,
        Eli Cohen <eli@...lanox.com>
Subject: Re: [v2] PCI: Add an option to control probing of VFs before enabling
 SR-IOV

On 4/12/2017 10:22 AM, Bjorn Helgaas wrote:
> 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, bodong@...lanox.com wrote:
>>>> From: Bodong Wang <bodong@...lanox.com>
>>>>
>>>> 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).
> 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
> devices?
This seems interesting to me as well. Not sure if USB driver is 
applicable or not. And, drivers_autoprobe might work for USB if it 
doesn't probe the sub-device as default like sriov. Worth to take a look.
> 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
>      "drivers_autoprobe"
>
>    - Update Documentation/ABI/testing/sysfs-bus-pci to document your
>      new knob
>
>    - Update Documentation/ABI/... to document drivers_autoprobe
Ack, will send v3.

Thanks,

Bodong