netdev - Re: [RFC PATCH] virtio_net: Extend virtio to use VF datapath when available

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Date:   Tue, 19 Dec 2017 14:37:50 -0800
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     David Miller <davem@...emloft.net>, mst@...hat.com,
        netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        alexander.duyck@...il.com, jesse.brandeburg@...el.com
Subject: Re: [RFC PATCH] virtio_net: Extend virtio to use VF datapath when
 available

On 12/19/2017 11:46 AM, Stephen Hemminger wrote:
> On Tue, 19 Dec 2017 11:42:33 -0800
> "Samudrala, Sridhar" <sridhar.samudrala@...el.com> wrote:
>
>> On 12/19/2017 10:41 AM, Stephen Hemminger wrote:
>>> On Tue, 19 Dec 2017 13:21:17 -0500 (EST)
>>> David Miller <davem@...emloft.net> wrote:
>>>   
>>>> From: Stephen Hemminger <stephen@...workplumber.org>
>>>> Date: Tue, 19 Dec 2017 09:55:48 -0800
>>>>   
>>>>> could be 10ms, just enough to let udev do its renaming
>>>> Please, move to some kind of notification or event based handling of
>>>> this problem.
>>>>
>>>> No delay is safe, what if userspace gets swapped out or whatever
>>>> else might make userspace stall unexpectedly?
>>>>   
>>> The plan is to remove the delay and do the naming in the kernel.
>>> This was suggested by Lennart since udev is only doing naming policy
>>> because kernel names were not repeatable.
>>>
>>> This makes the VF show up as "ethN_vf" on Hyper-V which is user friendly.
>>>
>>> Patch is pending.
>> Do we really need to delay the setup until the name is changed?
>> Can't we call dev_set_mtu() and dev_open() until dev_change_name() is done?
>>
>> Thanks
>> Sridhar
> You can call dev_set_mtu, but when dev_open is done the device name
> can not be changed by userspace.
I did a quick test to remove the delay and also the dev_open() call and 
i don't see
any issues with virtio taking over the VF datapath.
Only the netdev_info() messages may show old device name.

Any specific scenario where we need to explicitly call  VF's dev_open() 
in the VF setup process?
I tried i40evf driver loaded after virtio_net  AND  virtio_net loading 
after i40evf.

Thanks
Sridhar