3.18.36-rt38-rc1 stable review patch. If anyone has any objections, please let me know. ------------------ From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> The root-lock is dropped before dev_hard_start_xmit() is invoked and after setting the __QDISC___STATE_RUNNING bit. If this task is now pushed away by a task with a higher priority then the task with the higher priority won't be able to submit packets to the NIC directly instead they will be enqueued into the Qdisc. The NIC will remain idle until the task(s) with higher priority leave the CPU and the task with lower priority gets back and finishes the job. If we take always the busylock we ensure that the RT task can boost the low-prio task and submit the packet. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx> --- net/core/dev.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/core/dev.c b/net/core/dev.c index da674bb38606..438c5afa5b01 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -2801,7 +2801,11 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q, * This permits __QDISC___STATE_RUNNING owner to get the lock more * often and dequeue packets faster. */ +#ifdef CONFIG_PREEMPT_RT_FULL + contended = true; +#else contended = qdisc_is_running(q); +#endif if (unlikely(contended)) spin_lock(&q->busylock); -- 2.8.1 -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
