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

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

On 4/18/2018 7:49 AM, Tan, Jianfeng wrote:
> Hi Ferruh,
> 
> 
> On 4/17/2018 7:26 PM, Ferruh Yigit wrote:
>> 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.
> 
> AFAIK, link status means we can get link status through APIs like 
> rte_eth_link_get(); while link status event means applications can 
> register link status events, and those events get called if link status 
> is changed.
> 
> If I understand it correctly, for vhost, we can keep both link status 
> and link status event for vhost.
> 
> Could you specify the reason why we remove link status event?

Hi Jianfeng,

I think problem is the definition of the features are not clear, that is why I
started a doc to document them (doc/guides/nics/features.rst)

"Link status", I think we agree on this one. PMD should provide up-to-date,
valid link data on rte_eth_dev_data->dev_link. So that this link information can
be get by rte_eth_link_get(), rte_eth_link_get_nowait() ethdev APIs.

rte_eth_link_get() uses dev_ops->link_update() to get the latest link
information, for virtual PMDs, including vhost, this function does nothing,
because there is no actual physical link. That is why I was not sure advertising
link status feature for vhost, and other virtual PMDs doesn't report this
feature. After Tiwei's comment that link status shows that qemu connected to
vhost, added this feature back to vhost PMD.


"Link status event", can be
a- PMD calls application callback in link change
b- PMD registers interrupt handler for link status change interrupts

Based on how other PMDs report this feature, I believe it is (b), and I have
documented that way. And vhost "Link status event" feature removed based on this.

There are some set of config options and flags to control the LSC interrupt,
that also effects rte_eth_link_get() and rte_eth_link_get_nowait() APIs, I
believe that is the main concern here.

As commented above, I don't understand why calling user register callback for
link change event is something on PMD decision, it should be default behavior
for PMD. What is the point of leaving this into PMD and think this as a feature
of PMD?


Overall, practical reason of this table is to inform developer/user about PMD
features, which is indeed device + driver features, and help her to in
development or on setting expectations. We can always discuss what helps more to
developer/user and update the features table.

Thanks,
ferruh

> 
> Thanks,
> Jianfeng
> 
>>
>> Will send a new patch to reflect this.
>>
>> Thanks,
>> ferruh
>