Re: [EXT] Re: [PATCH v1 net-next 4/6] net: mscc: ocelot: VCAP IS1 support

[Allan W. Nielsen]

On 07.05.2020 11:23, Xiaoliang Yang wrote:
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>
> Hi Allan,
>
>
> > Hi Vladimir,
> >
> > On 06.05.2020 13:53, Vladimir Oltean wrote:
> [snip]
> > >At the moment, the driver does not support more than 1 action. We might
> > >need to change that, but we can still install more filters with the
> > >same key and still be fine (see more below). When there is more than 1
> > >action, the IS1 stuff will be combined into a single rule programmed
> > >into IS1, and the IS2 stuff will be combined into a single new rule
> > >with the same keys installed into VCAP IS2. Would that not work?
> > >
> > >> The SW model have these two rules in the same table, and can stop
> > >> process at the first match. SW will do the action of the first frame
> > >> matching.
> > >>
> > >
> > >Actually I think this is an incorrect assumption - software stops at
> > >the first action only if told to do so. Let me copy-paste a text from a
> > >different email thread.
> >
> > I'm still not able to see how this proposal will give us the same behavioral in SW and in HW.
> >
> > A simple example:
> >
> > tc qdisc add dev enp0s3 ingress
> > tc filter add dev enp0s3 protocol 802.1Q parent ffff: \
> >      prio 10 flower vlan_id 5 action vlan modify id 10 tc filter add dev enp0s3 protocol 802.1Q parent ffff: \
> >      prio 20 flower src_mac 00:00:00:00:00:08 action drop
> >
> > We can then inject a frame with VID 5 and smac ::08:
> > $ ef tx tap0 eth smac 00:00:00:00:00:08 ctag vid 5
> >
> > We can then check the filter and see that it only hit the first rule:
> >
> > $ tc -s filter show dev enp0s3 ingress
> > filter protocol 802.1Q pref 10 flower chain 0 filter protocol 802.1Q pref 10 flower chain 0 handle 0x1
> >    vlan_id 5
> >    not_in_hw
> >          action order 1: vlan  modify id 10 protocol 802.1Q priority 0 pipe
> >           index 1 ref 1 bind 1 installed 19 sec used 6 sec
> >          Action statistics:
> >          Sent 42 bytes 1 pkt (dropped 0, overlimits 0 requeues 0)
> >          backlog 0b 0p requeues 0
> >
> > filter protocol 802.1Q pref 20 flower chain 0 filter protocol 802.1Q pref 20 flower chain 0 handle 0x1
> >   src_mac 00:00:00:00:00:08
> >   not_in_hw
> >         action order 1: gact action drop
> >          random type none pass val 0
> >          index 1 ref 1 bind 1 installed 11 sec used 11 sec
> >         Action statistics:
> >         Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
> >         backlog 0b 0p requeues 0
> >
> > If this was done with the proposed HW offload, then both rules would have been hit and we would have a different behavioral.
> >
> > This can be fixed by adding the "continue" action to the first rule:
>
> > tc filter add dev enp0s3 protocol 802.1Q parent ffff: \
> >      prio 10 flower vlan_id 5 action vlan modify id 10 continue tc filter add dev enp0s3 protocol 802.1Q parent ffff: \
> >      prio 20 flower src_mac 00:00:00:00:00:08 action drop
> >
> > But that would again break if we add 2 rules manipulating the VLAN (as the HW does not continue with in a single TCAM).
> >
> > My point is: I do not think we can hide the fact that this is done in independent TCAMs in the silicon.
> >
> > I think it is possible to do this with the chain feature (even though it is not a perfect match), but it would require more analysis.
> >
> > /Allan
>
> Do you mean it's better to set vlan modify filters in a different chain, and write the filter entries with a same chain in the same VCAP TCAM?
> For example:
>        tc filter add dev enp0s3 protocol 802.1Q chain 11 parent ffff: prio 10 flower skip_sw vlan_id 5 action vlan modify id 10
>        tc filter add dev enp0s3 protocol 802.1Q chain 22 parent ffff: prio 20 flower skip_sw src_mac 00:00:00:00:00:08 action drop
> for this usage, we only need to ensure a chain corresponding to a VCAP in ocelot ace driver. I'm not sure is my understanding right?

I still have not found a satisfying solution to this. As I understand
the chains, they require the "goto" action to be used to tie them
together.

We could use that to represent a single lookup in is1 and link that to a
lookup in is2. Not sure if we should, it will also require
(non-backwards compatible) changes in how the existing IS2 support is
working.

Again, I do not have the answer (I'm also looking for it), but I think
we need something where it is clear to the user that this end up in
different lists.

/Allan