net: taprio offload: enforce qdisc to netdev queue mapping
Even though the taprio qdisc is designed for multiqueue devices, all the queues still point to the same top-level taprio qdisc. This works and is probably required for software taprio, but at least with offload taprio, it has an undesirable side effect: because the whole qdisc is run when a packet has to be sent, it allows packets in a best-effort class to be processed in the context of a task sending higher priority traffic. If there are packets left in the qdisc after that first run, the NET_TX softirq is raised and gets executed immediately in the same process context. As with any other softirq, it runs up to 10 times and for up to 2ms, during which the calling process is waiting for the sendmsg call (or similar) to return. In my use case, that calling process is a real-time task scheduled to send a packet every 2ms, so the long sendmsg calls are leading to missed timeslots. By attaching each netdev queue to its own qdisc, as it is done with the "classic" mq qdisc, each traffic class can be processed independently without touching the other classes. A high-priority process can then send packets without getting stuck in the sendmsg call anymore. Signed-off-by:Yannick Vignon <yannick.vignon@nxp.com> Signed-off-by:
David S. Miller <davem@davemloft.net>
parent
d8654f4f
Please register or sign in to comment