From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 20 Jan 2016 15:39:05 +0100
Subject: net: provide a way to delegate processing a softirq to ksoftirqd
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 9b05d8f74ca3956f90de70b6f1ad03d0379b8eee
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

If the NET_RX uses up all of his budget it moves the following NAPI
invocations into the `ksoftirqd`. On -RT it does not do so. Instead it
rises the NET_RX softirq in its current context again.

In order to get closer to mainline's behaviour this patch provides
__raise_softirq_irqoff_ksoft() which raises the softirq in the ksoftird.

Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 include/linux/interrupt.h |    8 ++++++++
 kernel/softirq.c          |   21 +++++++++++++++++++++
 net/core/dev.c            |    2 +-
 3 files changed, 30 insertions(+), 1 deletion(-)

--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -508,6 +508,14 @@ extern void thread_do_softirq(void);
 extern void open_softirq(int nr, void (*action)(struct softirq_action *));
 extern void softirq_init(void);
 extern void __raise_softirq_irqoff(unsigned int nr);
+#ifdef CONFIG_PREEMPT_RT_FULL
+extern void __raise_softirq_irqoff_ksoft(unsigned int nr);
+#else
+static inline void __raise_softirq_irqoff_ksoft(unsigned int nr)
+{
+	__raise_softirq_irqoff(nr);
+}
+#endif
 
 extern void raise_softirq_irqoff(unsigned int nr);
 extern void raise_softirq(unsigned int nr);
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -686,6 +686,27 @@ void __raise_softirq_irqoff(unsigned int
 }
 
 /*
+ * Same as __raise_softirq_irqoff() but will process them in ksoftirqd
+ */
+void __raise_softirq_irqoff_ksoft(unsigned int nr)
+{
+	unsigned int mask;
+
+	if (WARN_ON_ONCE(!__this_cpu_read(ksoftirqd) ||
+			 !__this_cpu_read(ktimer_softirqd)))
+		return;
+	mask = 1UL << nr;
+
+	trace_softirq_raise(nr);
+	or_softirq_pending(mask);
+	if (mask & TIMER_SOFTIRQS)
+		__this_cpu_read(ktimer_softirqd)->softirqs_raised |= mask;
+	else
+		__this_cpu_read(ksoftirqd)->softirqs_raised |= mask;
+	wakeup_proper_softirq(nr);
+}
+
+/*
  * This function must run with irqs disabled!
  */
 void raise_softirq_irqoff(unsigned int nr)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5599,7 +5599,7 @@ static __latent_entropy void net_rx_acti
 	list_splice_tail(&repoll, &list);
 	list_splice(&list, &sd->poll_list);
 	if (!list_empty(&sd->poll_list))
-		__raise_softirq_irqoff(NET_RX_SOFTIRQ);
+		__raise_softirq_irqoff_ksoft(NET_RX_SOFTIRQ);
 
 	net_rps_action_and_irq_enable(sd);
 out: