On Wed Nov 12 2025, Vinicius Costa Gomes wrote: > Hi, > > Kurt Kanzenbach <[email protected]> writes: > >> The MQPRIO (and ETF) offload utilizes the TSN Tx mode. This mode is always >> coupled to Qbv. Therefore, the driver sets a default Qbv schedule of all >> gates >> opened and a cycle time of 1s. This schedule is set during probe. >> >> However, the following sequence of events lead to Tx issues: >> >> - Boot a dual core system >> probe(): >> igc_tsn_clear_schedule(): >> -> Default Schedule is set >> Note: At this point the driver has allocated two Tx/Rx queues, because >> there are only two CPU(s). >> >> - ethtool -L enp3s0 combined 4 >> igc_ethtool_set_channels(): >> igc_reinit_queues() >> -> Default schedule is gone, per Tx ring start and end time are zero >> >> - tc qdisc replace dev enp3s0 handle 100 parent root mqprio \ >> num_tc 4 map 3 3 2 2 0 1 1 1 3 3 3 3 3 3 3 3 \ >> queues 1@0 1@1 1@2 1@3 hw 1 >> igc_tsn_offload_apply(): >> igc_tsn_enable_offload(): >> -> Writes zeros to IGC_STQT(i) and IGC_ENDQT(i) -> Boom >> >> Therefore, restore the default Qbv schedule after changing the amount of >> channels. >> > > Couple of questions: > - Would it make sense to mark this patch as a fix?
This only happens if a user uses ETF or MQPRIO and a dual/single core system. So I didn't see the need to mark it as a fix. > > - What would happen if the user added a Qbv schedule (not the default > one) and then changed the number of queues? My concern is that 'tc > qdisc' would show the custom user schedule and the hardware would be > "running" the default schedule, this inconsistency is not ideal. In > any case, it would be a separate patch. Excellent point. Honestly I'm not sure what to expect when changing the number of queues after a user Qbv schedule is added. For MQPRIO we added a restriction [1] especially for that case. I'm leaning towards the same solution here. What do you think? Thanks, Kurt [1] - https://elixir.bootlin.com/linux/v6.18-rc5/source/drivers/net/ethernet/intel/igc/igc_ethtool.c#L1564
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