From: Sebastian Andrzej Siewior [mailto:bigeasy@xxxxxxxxxxxxx] > >> I found that sometimes when sending network packets, the kernel would > >> hijack the thread of the sender when the queue was empty. This would > >> cause issues, since I had no control over the priority of that > >> thread, since it could be anything. My fix was to never allow the > >> kernel to send in the context of the sending userspace > > > >We had a similar problem and solved it with changed locking: > > So the following patch should do the job. Can someone confirm? > > From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > 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@xxxxxxxxxxxxx> > --- > net/core/dev.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/net/core/dev.c b/net/core/dev.c index cc364be3587b..0e17592adbff > 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -2891,7 +2891,11 @@ 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); > > -- > 2.8.0.rc3 In could not reproduce the problematic situation with v4.4.4-rt11 (without patch) in our test environment. The patch may work, but I am able to confirm that with a test. ��.n��������+%������w��{.n�����{�����ǫ���ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
