| From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> |
| Date: Wed, 30 Mar 2016 13:36:29 +0200 |
| Subject: [PATCH] net: dev: always take qdisc's busylock in __dev_xmit_skb() |
| |
| 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@linutronix.de> |
| --- |
| net/core/dev.c | 4 ++++ |
| 1 file changed, 4 insertions(+) |
| |
| --- a/net/core/dev.c |
| +++ b/net/core/dev.c |
| @@ -3078,7 +3078,11 @@ static inline int __dev_xmit_skb(struct |
| * This permits qdisc->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); |
| |
