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

[Xiaoliang Yang]

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?

regards,
Xiaoliang