36 lines
1.3 KiB
Diff
36 lines
1.3 KiB
Diff
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()
|
|
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.1-rt3.tar.xz
|
|
|
|
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
|
|
@@ -3446,7 +3446,11 @@ 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);
|
|
|