[dpdk-dev] [PATCH v3 27/27] net/ena: set link speed as none

[Chas Williams]

On Mon, Jun 11, 2018 at 4:01 AM Michał Krawczyk <mk at semihalf.com> wrote:

> 2018-06-10 3:35 GMT+02:00 Chas Williams <3chas3 at gmail.com>:
> >
> >
> > On Fri, Jun 8, 2018 at 3:37 PM Ferruh Yigit <ferruh.yigit at intel.com>
> wrote:
> >>
> >> On 6/7/2018 10:43 AM, Michal Krawczyk wrote:
> >> > From: Rafal Kozik <rk at semihalf.com>
> >> >
> >> > Link speed should is not limited to 10Gb/s and it shouldn't be
> >> > hardcoded.
> >> >
> >> > They link speed is set to none instead and the applications shouldn't
> >> > rely on this value when using ENA PMD.
> >>
> >> Why not able to set link speed?
> >>
> >> And what is the link_autoneg, ETH_LINK_FIXED? What is the point of
> setting
> >> link
> >> speed FIXED and later speed value NONE?
> >
> >
> > The link speed is part of the spanning tree path computation.  I don't
> think
> > picking 0 (or undefined)
> > is the appropriate choice.  For virtual interfaces link speed is a
> > troublesome quantity but advertising
> > undefined seems worse then just use some constant value.
> >
>
> Setting constant value is not making much sense in the virtualized
> environment (ENA can be only used in the cloud). Link speed can be
> very flexible in that case and that's why ENA isn't providing it. If
> we will use constant value, what it should be? It may lead to
> confusion or can result in the performance issues because some
> applications are relying on this number to send max traffic.
>

What applications are using this value to determine the transmit speed?


> Applications should not make assumption that the link speed is always
> giving valid value and if it is not, they should try to configure rate
> dynamically, instead of statically.


So advertising a fixed speed of 10G should be perfectly fine.  The
application should not assume 10G is a valid value and will attempt
to dynamically configure the rate.

The link speed should never be used to determine a transmit rate
for an application because you don't know the speeds in the middle
of the network.


>
> >>
> >>
> >> >
> >> > Fixes: 1173fca ("ena: add polling-mode driver")
> >>
> >> For next time can you please use git alias to have consistent Fixes
> format
> >>
> >> >
> >> > Signed-off-by: Rafal Kozik <rk at semihalf.com>
> >> > Acked-by: Michal Krawczyk <mk at semihalf.com>
> >> > ---
> >> >  drivers/net/ena/ena_ethdev.c | 2 +-
> >> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >> >
> >> > diff --git a/drivers/net/ena/ena_ethdev.c
> b/drivers/net/ena/ena_ethdev.c
> >> > index 5c3b6494f..9ae73e331 100644
> >> > --- a/drivers/net/ena/ena_ethdev.c
> >> > +++ b/drivers/net/ena/ena_ethdev.c
> >> > @@ -848,7 +848,7 @@ static int ena_link_update(struct rte_eth_dev
> *dev,
> >> >       adapter = (struct ena_adapter *)(dev->data->dev_private);
> >> >
> >> >       link->link_status = adapter->link_status ? ETH_LINK_UP :
> >> > ETH_LINK_DOWN;
> >> > -     link->link_speed = ETH_SPEED_NUM_10G;
> >> > +     link->link_speed = ETH_SPEED_NUM_NONE;
> >> >       link->link_duplex = ETH_LINK_FULL_DUPLEX;
> >> >
> >> >       return 0;
> >> >
> >>
> >
>