Tobias Waldekranz
2022-Mar-10 22:46 UTC
[Bridge] [PATCH v2 net-next 07/10] net: dsa: Pass MST state changes to driver
On Thu, Mar 10, 2022 at 18:18, Vladimir Oltean <olteanv at gmail.com> wrote:> On Thu, Mar 10, 2022 at 05:05:35PM +0100, Tobias Waldekranz wrote: >> On Thu, Mar 10, 2022 at 12:35, Vladimir Oltean <olteanv at gmail.com> wrote: >> > On Thu, Mar 10, 2022 at 09:54:34AM +0100, Tobias Waldekranz wrote: >> >> >> + if (!dsa_port_can_configure_learning(dp) || dp->learning) { >> >> >> + switch (state->state) { >> >> >> + case BR_STATE_DISABLED: >> >> >> + case BR_STATE_BLOCKING: >> >> >> + case BR_STATE_LISTENING: >> >> >> + /* Ideally we would only fast age entries >> >> >> + * belonging to VLANs controlled by this >> >> >> + * MST. >> >> >> + */ >> >> >> + dsa_port_fast_age(dp); >> >> > >> >> > Does mv88e6xxx support this? If it does, you might just as well >> >> > introduce another variant of ds->ops->port_fast_age() for an msti. >> >> >> >> You can limit ATU operations to a particular FID. So the way I see it we >> >> could either have: >> >> >> >> int (*port_vlan_fast_age)(struct dsa_switch *ds, int port, u16 vid) >> >> >> >> + Maybe more generic. You could imagine there being a way to trigger >> >> this operation from userspace for example. >> >> - We would have to keep the VLAN<->MSTI mapping in the DSA layer in >> >> order to be able to do the fan-out in dsa_port_set_mst_state. >> >> >> >> or: >> >> >> >> int (*port_msti_fast_age)(struct dsa_switch *ds, int port, u16 msti) >> >> >> >> + Let's the mapping be an internal affair in the driver. >> >> - Perhaps, less generically useful. >> >> >> >> Which one do you prefer? Or is there a hidden third option? :) >> > >> > Yes, I was thinking of "port_msti_fast_age". I don't see a cheap way of >> > keeping VLAN to MSTI associations in the DSA layer. Only if we could >> > retrieve this mapping from the bridge layer - maybe with something >> > analogous to br_vlan_get_info(), but br_mst_get_info(), and this gets >> > passed a VLAN_N_VID sized bitmap, which the bridge populates with ones >> > and zeroes. >> >> That can easily be done. Given that, should we go for port_vlan_fast_age >> instead? port_msti_fast_age feels like an awkward interface, since I >> don't think there is any hardware out there that can actually perform >> that operation without internally fanning it out over all affected VIDs >> (or FIDs in the case of mv88e6xxx). > > Yup, yup. My previous email was all over the place with regard to the > available options, because I wrote it in multiple phases so it wasn't > chronologically ordered top-to-bottom. But port_vlan_fast_age() makes > the most sense if you can implement br_mst_get_info(). Same goes for > dsa_port_notify_bridge_fdb_flush(). > >> > The reason why I asked for this is because I'm not sure of the >> > implications of flushing the entire FDB of the port for a single MSTP >> > state change. It would trigger temporary useless flooding in other MSTIs >> > at the very least. There isn't any backwards compatibility concern to >> > speak of, so we can at least try from the beginning to limit the >> > flushing to the required VLANs. >> >> Aside from the performance implications of flows being temporarily >> flooded I don't think there are any. >> >> I suppose if you've disabled flooding of unknown unicast on that port, >> you would loose the flow until you see some return traffic (or when one >> side gives up and ARPs). While somewhat esoteric, it would be nice to >> handle this case if the hardware supports it. > > If by "handle this case" you mean "flush only the affected VLANs", then > yes, I fully agree. > >> > What I didn't think about, and will be a problem, is >> > dsa_port_notify_bridge_fdb_flush() - we don't know the vid to flush. >> > The easy way out here would be to export dsa_port_notify_bridge_fdb_flush(), >> > add a "vid" argument to it, and let drivers call it. Thoughts? >> >> To me, this seems to be another argument in favor of >> port_vlan_fast_age. That way you would know the VIDs being flushed at >> the DSA layer, and driver writers needn't concern themselves with having >> to remember to generate the proper notifications back to the bridge. > > See above. > >> > Alternatively, if you think that cross-flushing FDBs of multiple MSTIs >> > isn't a real problem, I suppose we could keep the "port_fast_age" method. >> >> What about falling back to it if the driver doesn't support per-VLAN >> flushing? Flushing all entries will work in most cases, at the cost of >> some temporary flooding. Seems more useful than refusing the offload >> completely. > > So here's what I don't understand. Do you expect a driver other than > mv88e6xxx to do something remotely reasonable under a bridge with MSTP > enabled? The idea being to handle gracefully the case where a port is > BLOCKING in an MSTI but FORWARDING in another. Because if not, let's > just outright not offload that kind of bridge, and only concern > ourselves with what MST-capable drivers can do.I think you're right. I was trying to make it easier for other driver writers, but it will just be more confusing and error prone. Alright, so v3 will have something like this: bool dsa_port_can_offload_mst(struct dsa_port *dp) { return ds->ops->vlan_msti_set && ds->ops->port_mst_state_set && ds->ops->port_vlan_fast_age && dsa_port_can_configure_learning(dp); } If this returns false, we have two options: 1. Return -EOPNOTSUPP, which the bridge will be unable to discriminate from a non-switchdev port saying "I have no idea what you're talking about". I.e. the bridge will happily apply the config, but the hardware won't match. I don't like this, but it lines up with most other stuff. 2. Return a hard error, e.g. -EINVAL/-ENOSYS. This will keep the bridge in sync with the hardware and also gives some feedback to the user. This seems like the better approach to me, but it is a new kind of paradigm. What do you think?> I'm shadowing you with a prototype (and untested so far) MSTP > implementation for the ocelot/felix drivers, and those switches can > flush the MAC table per VLAN too. So I don't see an immediate need to > have a fallback implementation if you'll also provide it for mv88e6xxx. > Let's treat that only if the need arises.Cool. Agreed, v3 will implement .port_vlan_fast_age for mv88e6xxx.
Vladimir Oltean
2022-Mar-10 23:08 UTC
[Bridge] [PATCH v2 net-next 07/10] net: dsa: Pass MST state changes to driver
On Thu, Mar 10, 2022 at 11:46:45PM +0100, Tobias Waldekranz wrote:> On Thu, Mar 10, 2022 at 18:18, Vladimir Oltean <olteanv at gmail.com> wrote: > > On Thu, Mar 10, 2022 at 05:05:35PM +0100, Tobias Waldekranz wrote: > >> On Thu, Mar 10, 2022 at 12:35, Vladimir Oltean <olteanv at gmail.com> wrote: > >> > On Thu, Mar 10, 2022 at 09:54:34AM +0100, Tobias Waldekranz wrote: > >> >> >> + if (!dsa_port_can_configure_learning(dp) || dp->learning) { > >> >> >> + switch (state->state) { > >> >> >> + case BR_STATE_DISABLED: > >> >> >> + case BR_STATE_BLOCKING: > >> >> >> + case BR_STATE_LISTENING: > >> >> >> + /* Ideally we would only fast age entries > >> >> >> + * belonging to VLANs controlled by this > >> >> >> + * MST. > >> >> >> + */ > >> >> >> + dsa_port_fast_age(dp); > >> >> > > >> >> > Does mv88e6xxx support this? If it does, you might just as well > >> >> > introduce another variant of ds->ops->port_fast_age() for an msti. > >> >> > >> >> You can limit ATU operations to a particular FID. So the way I see it we > >> >> could either have: > >> >> > >> >> int (*port_vlan_fast_age)(struct dsa_switch *ds, int port, u16 vid) > >> >> > >> >> + Maybe more generic. You could imagine there being a way to trigger > >> >> this operation from userspace for example. > >> >> - We would have to keep the VLAN<->MSTI mapping in the DSA layer in > >> >> order to be able to do the fan-out in dsa_port_set_mst_state. > >> >> > >> >> or: > >> >> > >> >> int (*port_msti_fast_age)(struct dsa_switch *ds, int port, u16 msti) > >> >> > >> >> + Let's the mapping be an internal affair in the driver. > >> >> - Perhaps, less generically useful. > >> >> > >> >> Which one do you prefer? Or is there a hidden third option? :) > >> > > >> > Yes, I was thinking of "port_msti_fast_age". I don't see a cheap way of > >> > keeping VLAN to MSTI associations in the DSA layer. Only if we could > >> > retrieve this mapping from the bridge layer - maybe with something > >> > analogous to br_vlan_get_info(), but br_mst_get_info(), and this gets > >> > passed a VLAN_N_VID sized bitmap, which the bridge populates with ones > >> > and zeroes. > >> > >> That can easily be done. Given that, should we go for port_vlan_fast_age > >> instead? port_msti_fast_age feels like an awkward interface, since I > >> don't think there is any hardware out there that can actually perform > >> that operation without internally fanning it out over all affected VIDs > >> (or FIDs in the case of mv88e6xxx). > > > > Yup, yup. My previous email was all over the place with regard to the > > available options, because I wrote it in multiple phases so it wasn't > > chronologically ordered top-to-bottom. But port_vlan_fast_age() makes > > the most sense if you can implement br_mst_get_info(). Same goes for > > dsa_port_notify_bridge_fdb_flush(). > > > >> > The reason why I asked for this is because I'm not sure of the > >> > implications of flushing the entire FDB of the port for a single MSTP > >> > state change. It would trigger temporary useless flooding in other MSTIs > >> > at the very least. There isn't any backwards compatibility concern to > >> > speak of, so we can at least try from the beginning to limit the > >> > flushing to the required VLANs. > >> > >> Aside from the performance implications of flows being temporarily > >> flooded I don't think there are any. > >> > >> I suppose if you've disabled flooding of unknown unicast on that port, > >> you would loose the flow until you see some return traffic (or when one > >> side gives up and ARPs). While somewhat esoteric, it would be nice to > >> handle this case if the hardware supports it. > > > > If by "handle this case" you mean "flush only the affected VLANs", then > > yes, I fully agree. > > > >> > What I didn't think about, and will be a problem, is > >> > dsa_port_notify_bridge_fdb_flush() - we don't know the vid to flush. > >> > The easy way out here would be to export dsa_port_notify_bridge_fdb_flush(), > >> > add a "vid" argument to it, and let drivers call it. Thoughts? > >> > >> To me, this seems to be another argument in favor of > >> port_vlan_fast_age. That way you would know the VIDs being flushed at > >> the DSA layer, and driver writers needn't concern themselves with having > >> to remember to generate the proper notifications back to the bridge. > > > > See above. > > > >> > Alternatively, if you think that cross-flushing FDBs of multiple MSTIs > >> > isn't a real problem, I suppose we could keep the "port_fast_age" method. > >> > >> What about falling back to it if the driver doesn't support per-VLAN > >> flushing? Flushing all entries will work in most cases, at the cost of > >> some temporary flooding. Seems more useful than refusing the offload > >> completely. > > > > So here's what I don't understand. Do you expect a driver other than > > mv88e6xxx to do something remotely reasonable under a bridge with MSTP > > enabled? The idea being to handle gracefully the case where a port is > > BLOCKING in an MSTI but FORWARDING in another. Because if not, let's > > just outright not offload that kind of bridge, and only concern > > ourselves with what MST-capable drivers can do. > > I think you're right. I was trying to make it easier for other driver > writers, but it will just be more confusing and error prone. > > Alright, so v3 will have something like this: > > bool dsa_port_can_offload_mst(struct dsa_port *dp) > { > return ds->ops->vlan_msti_set && > ds->ops->port_mst_state_set && > ds->ops->port_vlan_fast_age && > dsa_port_can_configure_learning(dp); > } > > If this returns false, we have two options: > > 1. Return -EOPNOTSUPP, which the bridge will be unable to discriminate > from a non-switchdev port saying "I have no idea what you're talking > about". I.e. the bridge will happily apply the config, but the > hardware won't match. I don't like this, but it lines up with most > other stuff. > > 2. Return a hard error, e.g. -EINVAL/-ENOSYS. This will keep the bridge > in sync with the hardware and also gives some feedback to the > user. This seems like the better approach to me, but it is a new kind > of paradigm. > > What do you think?Wait, what? It matters a lot where you place the call to dsa_port_can_offload_mst(), too. You don't have to propagate a hard error code, either, at least if you make dsa_port_bridge_join() return -EOPNOTSUPP prior to calling switchdev_bridge_port_offload(), no? DSA transforms this error code into 0, and dsa_port_offloads_bridge*() starts returning false, which makes us ignore all MSTP related switchdev notifiers. The important part will be to make sure that MSTP is enabled for this bridge from the get-go (that being the only case in which we can offload an MSTP aware bridge), and refusing to offload dynamic changes to its MSTP state. I didn't re-check now, but I think I remember there being limitations even in the software bridge related to dynamic MSTP mode changes anyway - there had to not be any port VLANs, which IIUC means that you actually need to _delete_ the port PVIDs which are automatically created before you could change the MSTP mode. This is the model, what's wrong with it? I said "don't offload the bridge", not "don't offload specific MSTP operations".> > I'm shadowing you with a prototype (and untested so far) MSTP > > implementation for the ocelot/felix drivers, and those switches can > > flush the MAC table per VLAN too. So I don't see an immediate need to > > have a fallback implementation if you'll also provide it for mv88e6xxx. > > Let's treat that only if the need arises. > > Cool. Agreed, v3 will implement .port_vlan_fast_age for mv88e6xxx.