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

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

On 4/18/2018 12:36 PM, Tiwei Bie wrote:
> On Wed, Apr 18, 2018 at 11:42:56AM +0100, Ferruh Yigit wrote:
>> 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.
> 
> Do you mean you don't understand why vhost PMD calls
> _rte_eth_dev_callback_process(eth_dev, RTE_ETH_EVENT_INTR_LSC, NULL)
> in new_device() and destroy_device()? While other physical
> NIC drivers call this in their interrupt handlers which
> are registered via rte_intr_callback_register().

No, I understand this part.

My question is why not all PMDs call callback_process() when link changed as a
requirement? Why PMD is giving decision to call or not call callback_process() ?

> 
> The new_device() and destroy_device() in vhost PMD can be
> treated as something like the interrupt handlers in physical
> NIC drivers. They are the callbacks which are registered via
> rte_vhost_driver_callback_register() and will be called by
> vhost library when vhost events happen (and they should be
> translated to link status change events when we try to wrap
> it as a net PMD).
> 
> Thanks
> 
>> 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
>>>
>>