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

[Tiwei Bie <tiwei.bie@intel.com>]

On Wed, Apr 18, 2018 at 12:44:54PM +0100, Ferruh Yigit wrote:
> 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() ?

I got your point now. Maybe because in the library level,
it just knows an interrupt happened but doesn't know whether
it's a LSC interrupt or not (sometimes it needs to check
some vendor specific registers). So the simplest way is
just to ask each PMD to call callback_process() directly.
But unfortunately, some PMDs didn't do it as we expected..
(I didn't look into other PMDs, so I'm not sure about the
details.)

Thanks


> 
> > 
> > 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
> >>>
> >>
>