rps: Various optimizations

Introduce ____napi_schedule() helper for callers in irq disabled
contexts. rps_trigger_softirq() becomes a leaf function.

Use container_of() in process_backlog() instead of accessing per_cpu
address.

Use a custom inlined version of __napi_complete() in process_backlog()
to avoid one locked instruction :

 only current cpu owns and manipulates this napi,
 and NAPI_STATE_SCHED is the only possible flag set on backlog.
 we can use a plain write instead of clear_bit(),
 and we dont need an smp_mb() memory barrier, since RPS is on,
 backlog is protected by a spinlock.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 22 insertions, 6 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 36d53be4fca6..32611c8f1219 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2205,6 +2205,14 @@ int netdev_max_backlog __read_mostly = 1000;
 int netdev_budget __read_mostly = 300;
 int weight_p __read_mostly = 64;            /* old backlog weight */
 
+/* Called with irq disabled */
+static inline void ____napi_schedule(struct softnet_data *sd,
+                                     struct napi_struct *napi)
+{
+        list_add_tail(&napi->poll_list, &sd->poll_list);
+        __raise_softirq_irqoff(NET_RX_SOFTIRQ);
+}
+
 #ifdef CONFIG_RPS
 
 /* One global table that all flow-based protocols share. */
@@ -2363,7 +2371,7 @@ static void rps_trigger_softirq(void *data)
 {
         struct softnet_data *sd = data;
 
-        __napi_schedule(&sd->backlog);
+        ____napi_schedule(sd, &sd->backlog);
         sd->received_rps++;
 }
 
@@ -2421,7 +2429,7 @@ enqueue:
                 /* Schedule NAPI for backlog device */
                 if (napi_schedule_prep(&sd->backlog)) {
                         if (!rps_ipi_queued(sd))
-                                __napi_schedule(&sd->backlog);
+                                ____napi_schedule(sd, &sd->backlog);
                 }
                 goto enqueue;
         }
@@ -3280,7 +3288,7 @@ static void net_rps_action_and_irq_enable(struct softnet_data *sd)
 static int process_backlog(struct napi_struct *napi, int quota)
 {
         int work = 0;
-        struct softnet_data *sd = &__get_cpu_var(softnet_data);
+        struct softnet_data *sd = container_of(napi, struct softnet_data, backlog);
 
 #ifdef CONFIG_RPS
         /* Check if we have pending ipi, its better to send them now,
@@ -3313,7 +3321,16 @@ static int process_backlog(struct napi_struct *napi, int quota)
                                                    &sd->process_queue);
                 }
                 if (qlen < quota - work) {
-                        __napi_complete(napi);
+                        /*
+                         * Inline a custom version of __napi_complete().
+                         * only current cpu owns and manipulates this napi,
+                         * and NAPI_STATE_SCHED is the only possible flag set on backlog.
+                         * we can use a plain write instead of clear_bit(),
+                         * and we dont need an smp_mb() memory barrier.
+                         */
+                        list_del(&napi->poll_list);
+                        napi->state = 0;
+
                         quota = work + qlen;
                 }
                 rps_unlock(sd);
@@ -3334,8 +3351,7 @@ void __napi_schedule(struct napi_struct *n)
         unsigned long flags;
 
         local_irq_save(flags);
-        list_add_tail(&n->poll_list, &__get_cpu_var(softnet_data).poll_list);
-        __raise_softirq_irqoff(NET_RX_SOFTIRQ);
+        ____napi_schedule(&__get_cpu_var(softnet_data), n);
         local_irq_restore(flags);
 }
 EXPORT_SYMBOL(__napi_schedule);