Re: [dpdk-dev] [PATCH] drivers/net: update link status

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 4/17/2018 5:54 AM, Tiwei Bie wrote:
> On Mon, Apr 16, 2018 at 05:10:24PM +0100, Ferruh Yigit wrote:
>> On 4/14/2018 11:55 AM, Tiwei Bie wrote:
>>> On Fri, Apr 13, 2018 at 10:53:55PM +0100, Ferruh Yigit wrote:
>>>> On 4/10/2018 4:41 PM, Tiwei Bie wrote:
>>>>> On Tue, Mar 13, 2018 at 06:05:34PM +0000, Ferruh Yigit wrote:
>>>>>> Update link status related feature document items and minor updates in
>>>>>> some link status related functions.
>>>>>>
>>>>>> Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
>>>>>> ---
>>>>>>  doc/guides/nics/features/fm10k.ini      | 2 ++
>>>>>>  doc/guides/nics/features/fm10k_vf.ini   | 2 ++
>>>>>>  doc/guides/nics/features/i40e_vf.ini    | 1 +
>>>>>>  doc/guides/nics/features/igb_vf.ini     | 1 +
>>>>>>  doc/guides/nics/features/qede.ini       | 1 -
>>>>>>  doc/guides/nics/features/qede_vf.ini    | 1 -
>>>>>>  doc/guides/nics/features/vhost.ini      | 2 --
>>>>>>  doc/guides/nics/features/virtio_vec.ini | 1 +
>>>>>>  drivers/net/e1000/em_ethdev.c           | 2 +-
>>>>>>  drivers/net/ena/ena_ethdev.c            | 2 +-
>>>>>>  drivers/net/fm10k/fm10k_ethdev.c        | 6 ++----
>>>>>>  drivers/net/i40e/i40e_ethdev_vf.c       | 2 +-
>>>>>>  drivers/net/ixgbe/ixgbe_ethdev.c        | 2 +-
>>>>>>  drivers/net/mlx4/mlx4_ethdev.c          | 2 +-
>>>>>>  drivers/net/mlx5/mlx5_ethdev.c          | 2 +-
>>>>>>  15 files changed, 15 insertions(+), 14 deletions(-)
>>>>> [...]
>>>>>> diff --git a/doc/guides/nics/features/vhost.ini b/doc/guides/nics/features/vhost.ini
>>>>>> index dffd1f493..31302745a 100644
>>>>>> --- a/doc/guides/nics/features/vhost.ini
>>>>>> +++ b/doc/guides/nics/features/vhost.ini
>>>>>> @@ -4,8 +4,6 @@
>>>>>>  ; Refer to default.ini for the full list of available PMD features.
>>>>>>  ;
>>>>>>  [Features]
>>>>>> -Link status          = Y
>>>>>> -Link status event    = Y
>>>>>
>>>>> I think vhost PMD supports above features.
>>>>
>>>> I am not able to find where it is supported.
>>>>
>>>> Some virtual PMDs report fixed link, with empty link_update() dev_ops, and they
>>>> are not reported as supporting Link status, as far as I can see vhost also one
>>>> of them.
>>>>
>>>> And for Link status event, PMD needs to support LSC interrupts and should
>>>> register interrupt handler for it, which I can't find for vhost.
>>>>
>>>> I will send next version without updating above one, please point me where these
>>>> support added if I missed them.
>>>
>>> In drivers/net/vhost/rte_eth_vhost.c you could find below functions:
>>>
>>> static int
>>> new_device(int vid)
>>> {
>>> 	......
>>>
>>> 	eth_dev->data->dev_link.link_status = ETH_LINK_UP;
>>>
>>> 	......
>>>
>>> 	_rte_eth_dev_callback_process(eth_dev, RTE_ETH_EVENT_INTR_LSC, NULL);
>>>
>>> 	......
>>> }
>>>
>>> static void
>>> destroy_device(int vid)
>>> {
>>> 	......
>>>
>>> 	eth_dev->data->dev_link.link_status = ETH_LINK_DOWN;
>>>
>>> 	......
>>>
>>> 	_rte_eth_dev_callback_process(eth_dev, RTE_ETH_EVENT_INTR_LSC, NULL);
>>>
>>> 	......
>>> }
>>>
>>> They are the callbacks for vhost library.
>>>
>>> When a frontend (e.g. QEMU) is connected to this vhost backend
>>> and the frontend virtio device becomes ready, new_device() will
>>> be called by the vhost library, and the link status will be
>>> updated to UP.
>>>
>>> And when e.g. the connection is closed, destroy_device() will be
>>> called by the vhost library, and the link status will be updated
>>> to DOWN.
>>
>>
>> Got it. This behavior is similar for virtual PMDs. Provide static link
>> information and update link as UP during start and update it as DOWN during stop.
> 
> No, the link status isn't updated during vhost PMD start
> and stop. When the vhost PMD has been started, the link
> status still may be DOWN. The link status becomes UP only
> when the QEMU (it's another virtual machine process which
> has a virtio device) connects to this vhost PMD via a UNIX
> socket and the virtio driver in the virtual machine has
> setup the virtio device of the virtual machine.
> 
> So if vhost PMD reports the link status as DOWN, it means
> there is no QEMU (virtual machine) connects to it or the
> virtio device in the virtual machine hasn't been setup.
> (PS. The frontend can also be virtio-user PMD besides QEMU)

I believe announcing link feature reporting on virtual pmds still in gray area,
but because of qemu involvement in vhost case, I will keep link feature but will
drop link event.

Will send a new patch to reflect this.

Thanks,
ferruh

> 
> Thanks
> 
>>
>> Other virtual PMDs doesn't report this feature, so removed from vhost as well
>> for consistency.
>>
>>>
>>> So vhost PMD reports meaningful link status and also generates
>>> link status events.
>>
>> Yes PMD process user callbacks on link change [1], but I am not sure that is
>> what meant from "link status event", what I understand is link interrupts
>> supported in PMD level which seems not the case for vhost.
>>
>> [1]
>> This is something else but why calling user callback in link update is in PMD
>> discretion, shouldn't it be something done automatically in ethdev layer, somehow.
>>
>>>
>>> Thanks
>>>
>>