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

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

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)

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
> > 
>