Re: [dpdk-dev] [dpdk-stable] [PATCH] net/vmxnet3: keep link state consistent

[Thomas Monjalon <thomas@monjalon.net>]

17/04/2018 21:25, Ferruh Yigit:
> On 4/5/2018 4:01 PM, Chas Williams wrote:
> > On Thu, Apr 5, 2018 at 6:03 AM, Thomas Monjalon <thomas@monjalon.net> wrote:
> >> 20/03/2018 15:12, Ferruh Yigit:
> >>> On 3/18/2018 1:45 AM, Chas Williams wrote:
> >>>> From: Chas Williams <chas3@att.com>
> >>>>
> >>>> The vmxnet3 never attempts link speed negotiation.  As a virtual device
> >>>> the link speed is vague at best.  However, it is important for certain
> >>>> applications, like bonding, to see a consistent link_status.  802.3ad
> >>>> requires that only links of the same cost (link speed) be enslaved.
> >>>> Keeping the link status consistent in vmxnet3 avoids races with bonding
> >>>> enslavement.
> >>
> >> I don't understand the issue.
> >> Are you sure it is not an issue in bonding?
> > 
> > 802.3ad "requires" you to bond together links of the same speed and duplex.  The
> > primary reason for this (or so I gather) is to ensure that the
> > spanning-tree cost for
> > each port is the same.  If you fail from one link to another, you
> > don't want a spanning
> > tree reconfiguration.
> > 
> > The problem exists in general for most of the PMDs -- see
> > https://dpdk.org/ml/archives/dev/2018-April/094696.html
> > 
> > The problem is more vexing for AUTONEG and bonding.  I am still thinking about
> > that.  You don't know until you go to activate the slave and bonding
> > only makes its
> > check during the setup phase.  So for virtual adapters and bonding, not using
> > AUTONEG makes more sense because it is just easier to handle.
> > 
> >>
> >> About the right value to set for virtual PMDs, I don't know, both are fakes.
> >> I thought that AUTONEG better convey the vague link speed you describe.
> > 
> > It's not vague.  There is no negotiation of any sort.  The link speed
> > (and therefore cost)
> > of the link is fixed.  While the particular rate you get from the
> > adapter depends
> > on a number of factors, the link speed isn't going to change.  The
> > adapter is not
> > going to change the link speed from 10G to 1G or change from full duplex to half
> > duplex.
> 
> Hi Chas, Thomas,
> 
> What is the latest status of this patch? Is it agreed to convert link_autoneg to
> ETH_LINK_FIXED for following PMDs [1]?
> 
> [1]
> pcap
> softnic
> vmxnet3

Yes, OK for ETH_LINK_FIXED.


> >>>> Author: Thomas Monjalon <thomas@monjalon.net>
> >>>> Date:   Fri Jan 5 18:38:55 2018 +0100
> >>>>
> >>>> Fixes: 1e3a958f40b3 ("ethdev: fix link autonegotiation value")
> >>>> Cc: stable@dpdk.org
> >>>
> >>> There were a few more PMDs [1] they have been updated from FIXED to AUTONEG with
> >>> above commit, do you think should we update them back to FIXED as well?
> >>>
> >>> [1]
> >>> pcap
> >>> softnic
> >>> vmxnet3
> >>
> >> Yes, they all can be fixed/LINK_FIXED :) I guess
> >>
> >>
> >>
> 
>