net, rt: limit net_rx napi calls in threaded ISR context

-In a PREEMPT_RT with CONFIG_PREEMPT_RT_FULL configuration enabled,
 some of Interrupt Handler runs in context of threaded ISR.
 And if this threaded ISR raises a particular softirq, then that calls
 __raise_softirq_irqoff() function which mark the softirq ready to be
 executed while exiting ISR in context of ISR only.

-So, net_rx_action() function is called in context of threaded ISR
 if NET_RX_SOFTIRQ softirq is raised by that particular ISR.

-net_rx_action is balancing scheduling among napis
 by using time-out of 2 jiffies for particular napi.
 On timeout , it calls __raise_softirq_irqoff().

-In case of RT kernel, __raise_softirq_irqoff() again makes the
 NET_RX_SOFTIRQ ready. So it is called again and again until the packet
 ring is emptied.This creats a starvation condition for other threads.

-This patch removes calling __raise_softirq_irqoff() again while exiting
 net_rx_action()

Signed-off-by: Priyanka Jain <Priyanka.Jain@freescale.com>
Signed-off-by: Abhimanyu <abhimanyu@freescale.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 647ec24..402b7ce 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4445,7 +4445,9 @@ out:
 
 softnet_break:
 	sd->time_squeeze++;
+#ifndef CONFIG_PREEMPT_RT_FULL
 	__raise_softirq_irqoff(NET_RX_SOFTIRQ);
+#endif
 	goto out;
 }