Re: [PATCH net-next 6/6] net: dsa: sja1105: add broadcast and per-traffic class policers

[Vladimir Oltean]

On Sun, 29 Mar 2020 at 12:57, Ido Schimmel <idosch@xxxxxxxxxx> wrote:
>
> + Nik, Roopa
>
> On Sun, Mar 29, 2020 at 02:52:02AM +0200, Vladimir Oltean wrote:
> > From: Vladimir Oltean <vladimir.oltean@xxxxxxx>
> >
> > This patch adds complete support for manipulating the L2 Policing Tables
> > from this switch. There are 45 table entries, one entry per each port
> > and traffic class, and one dedicated entry for broadcast traffic for
> > each ingress port.
> >
> > Policing entries are shareable, and we use this functionality to support
> > shared block filters.
> >
> > We are modeling broadcast policers as simple tc-flower matches on
> > dst_mac. As for the traffic class policers, the switch only deduces the
> > traffic class from the VLAN PCP field, so it makes sense to model this
> > as a tc-flower match on vlan_prio.
> >
> > How to limit broadcast traffic coming from all front-panel ports to a
> > cumulated total of 10 Mbit/s:
> >
> > tc qdisc add dev sw0p0 ingress_block 1 clsact
> > tc qdisc add dev sw0p1 ingress_block 1 clsact
> > tc qdisc add dev sw0p2 ingress_block 1 clsact
> > tc qdisc add dev sw0p3 ingress_block 1 clsact
> > tc filter add block 1 flower skip_sw dst_mac ff:ff:ff:ff:ff:ff \
> >       action police rate 10mbit burst 64k
> >
> > How to limit traffic with VLAN PCP 0 (also includes untagged traffic) to
> > 100 Mbit/s on port 0 only:
> >
> > tc filter add dev sw0p0 ingress protocol 802.1Q flower skip_sw \
> >       vlan_prio 0 action police rate 100mbit burst 64k
> >
> > The broadcast, VLAN PCP and port policers are compatible with one
> > another (can be installed at the same time on a port).
>
> Hi Vladimir,
>
> Some switches have a feature called "storm control". It allows one to
> police incoming BUM traffic.

Yes, I am aware.
DPAA2 switches have a single (as far as I am aware) knob for 'flood
policers', and Ocelot has individual 'storm policers' for unknown
unicast, for multicast, broadcast and for 'learn frames'.

> See this entry from Cumulus Linux
> documentation:
>
> https://docs.cumulusnetworks.com/cumulus-linux-40/Layer-2/Spanning-Tree-and-Rapid-Spanning-Tree/#storm-control
>
> In the past I was thinking about ways to implement this in Linux. The
> only place in the pipeline where packets are actually classified to
> broadcast / unknown unicast / multicast is at bridge ingress. Therefore,

Actually I think only 'unknown unicast' is tricky here, and indeed the
bridge driver is the only place in the software datapath that would
know that.
I know very little about frame classification in the Linux network
stack, but would it be possible to introduce a match key in tc-flower
for whether packets have a known destination or not?

> my thinking was to implement these storm control policers as a
> "bridge_slave" operation. It can then be offloaded to capable drivers
> via the switchdev framework.
>

I think it would be a bit odd to duplicate tc functionality in the
bridge sysfs. I don't have a better suggestion though.

> I think that if we have this implemented in the Linux bridge, then your
> patch can be used to support the policing of broadcast packets while
> returning an error if user tries to police unknown unicast or multicast
> packets.

So even if the Linux bridge gains these knobs for flood policers,
still have the dst_mac ff:ff:ff:ff:ff:ff as a valid way to configure
one of those knobs?

> Or maybe the hardware you are working with supports these types
> as well?

Nope, on this hardware it's just broadcast, I just checked that. Which
simplifies things quite a bit.

>
> WDYT?
>

I don't know.

Thanks,
-Vladimir