[PATCH] rps: send IPIs ASAP

[Changli Gao <xiaosuo@gmail.com>]

rps: send IPIs ASAP

In order to reduce latency, we'd better send IPIs ASAP to schedule the
corresponding NAPIs.

For NAPI drivers, we send IPIs immediately, and for the others, we defer them
to NET_RX_SOFTIRQ. In this patch, we move net_rps_action() to the beginning of
net_rx_action() to emulate a softirq with the higher priority than
NET_RX_SOFTIRQ.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
----
 net/core/dev.c |   23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)
diff --git a/net/core/dev.c b/net/core/dev.c
index 05a2b29..d8fca21 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2363,6 +2363,10 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
 {
 	struct softnet_data *queue;
 	unsigned long flags;
+#ifdef CONFIG_RPS
+	bool ni = !in_irq();
+	bool ipi = false;
+#endif
 
 	queue = &per_cpu(softnet_data, cpu);
 
@@ -2380,6 +2384,10 @@ enqueue:
 #endif
 			rps_unlock(queue);
 			local_irq_restore(flags);
+#ifdef CONFIG_RPS
+			if (ipi)
+				__smp_call_function_single(cpu, &queue->csd, 0);
+#endif
 			return NET_RX_SUCCESS;
 		}
 
@@ -2389,6 +2397,11 @@ enqueue:
 			if (cpu != smp_processor_id()) {
 				struct softnet_data *myqueue;
 
+				if (ni) {
+					ipi = true;
+					goto enqueue;
+				}
+
 				myqueue = &__get_cpu_var(softnet_data);
 				queue->rps_ipi_next = myqueue->rps_ipi_list;
 				myqueue->rps_ipi_list = queue;
@@ -3337,6 +3350,7 @@ static void net_rps_action(void)
 	struct softnet_data *locqueue = &__get_cpu_var(softnet_data);
 	struct softnet_data *remqueue = locqueue->rps_ipi_list;
 
+	local_irq_disable();
 	if (remqueue) {
 		locqueue->rps_ipi_list = NULL;
 
@@ -3350,9 +3364,10 @@ static void net_rps_action(void)
 							   &remqueue->csd, 0);
 			remqueue = next;
 		}
-	} else
-#endif
+	} else {
 		local_irq_enable();
+	}
+#endif
 }
 
 static void net_rx_action(struct softirq_action *h)
@@ -3362,6 +3377,8 @@ static void net_rx_action(struct softirq_action *h)
 	int budget = netdev_budget;
 	void *have;
 
+	net_rps_action();
+
 	local_irq_disable();
 
 	while (!list_empty(list)) {
@@ -3423,7 +3440,7 @@ static void net_rx_action(struct softirq_action *h)
 		netpoll_poll_unlock(have);
 	}
 out:
-	net_rps_action();
+	local_irq_enable();
 
 #ifdef CONFIG_NET_DMA
 	/*