Re: PCI mini-summit notes

[Don Dutile <ddutile@redhat.com>]

On 08/30/2012 02:02 AM, Bjorn Helgaas wrote:
> [removed cc ksummit-2012-discuss]
>
> On Wed, Aug 29, 2012 at 3:54 PM, Yinghai Lu<yinghai@kernel.org>  wrote:
>> On Wed, Aug 29, 2012 at 3:44 PM, Jon Mason<jdmason@kudzu.us>  wrote:
>>>> Hi Bjorn,
>>>>          One of my team member reported another corner case for SR-IOV. There's
>>>> are two NIC cards in the system driven by the same driver, but one supports
>>>> SR-IOV and the other doesn't. It runs into trouble if "max_vfs" parameter is
>>>> set for the NIC driver.
>>>>          --Gerry
>>>
>>> I believe it was decided that a per-pf sysfs interface would be used
>>> to replace the current module parameter that specifies the number of
>>> vf's.  This should enable different numbers of vf's for each physical
>>> device.  The driver interface that was discussed would introduce new
>>> function pointers for handlers to setup/teardown the vf's.  I believe
>>> this will solve your problem once it has been implemented.
>>
>> now we have ixgbe.max_vfs=63
>>
>> so if change to per pci device (PF),
>>
>> how about having the driver built-in?
>> what kind of kernel parameters will be passed?

Having the driver built-in won't make a difference.

The model is to have files under sys fs, i.e.,
/sys/bus/pci/devices/0000:03:01.0/[sriov_vf_enable, sriov_vf_disable]

where one echo's the number of vf's one wants to configure for a pf
into the sriov_vf_enable file;  if want to disable/deconfigure the vf's,
one echo's a 1 to sriov_vf_disable (all or nothing disable).

the pci core will be able to check & filter that the max num of vf's
is not exceeded.  Also looking to add a file like 'sriov_num_vfs' to
indicate max number of vf's a PF supports.  Whether the bus configuration
supports it (enough mmio space, enough pci bus nums, etc.) won't be
known until the enable count is written.

I have the code down to create the sysfs files & report the num_vfs.
Hope to have the first enable/disable working within another week.
The tough part is to re-factor a pf driver that enables/configures pf;
I'm working with the igb(_main.c) driver right now.

- Don
>
> I don't think we really discussed things at this level, and I
> personally don't know enough about the current SR-IOV support to even
> know what the possible strategies are.  I think it's really up to the
> person doing the implementation to figure out what makes sense given
> the constraints of the SR-IOV specs and the current Linux support.
>
> Bjorn
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