net: optimize ____napi_schedule() to avoid extra NET_RX_SOFTIRQ

____napi_schedule() adds a napi into current cpu softnet_data poll_list,
then raises NET_RX_SOFTIRQ to make sure net_rx_action() will process it.

Idea of this patch is to not raise NET_RX_SOFTIRQ when being called indirectly
from net_rx_action(), because we can process poll_list from this point,
without going to full softirq loop.

This needs a change in net_rx_action() to make sure we restart
its main loop if sd->poll_list was updated without NET_RX_SOFTIRQ
being raised.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Tested-by: Jason Xing <kerneljasonxing@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/core/dev.c b/net/core/dev.c
index f34ce93..0c4b212 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4360,7 +4360,11 @@ static inline void ____napi_schedule(struct softnet_data *sd,
        }
 
        list_add_tail(&napi->poll_list, &sd->poll_list);
-       __raise_softirq_irqoff(NET_RX_SOFTIRQ);
+       /* If not called from net_rx_action()
+        * we have to raise NET_RX_SOFTIRQ.
+        */
+       if (!sd->in_net_rx_action)
+               __raise_softirq_irqoff(NET_RX_SOFTIRQ);
 }
 
 #ifdef CONFIG_RPS
@@ -6648,6 +6652,7 @@ static __latent_entropy void net_rx_action(struct softirq_action *h)
        LIST_HEAD(list);
        LIST_HEAD(repoll);
 
+start:
        sd->in_net_rx_action = true;
        local_irq_disable();
        list_splice_init(&sd->poll_list, &list);
@@ -6659,9 +6664,18 @@ static __latent_entropy void net_rx_action(struct softirq_action *h)
                skb_defer_free_flush(sd);
 
                if (list_empty(&list)) {
-                       sd->in_net_rx_action = false;
-                       if (!sd_has_rps_ipi_waiting(sd) && list_empty(&repoll))
-                               goto end;
+                       if (list_empty(&repoll)) {
+                               sd->in_net_rx_action = false;
+                               barrier();
+                               /* We need to check if ____napi_schedule()
+                                * had refilled poll_list while
+                                * sd->in_net_rx_action was true.
+                                */
+                               if (!list_empty(&sd->poll_list))
+                                       goto start;
+                               if (!sd_has_rps_ipi_waiting(sd))
+                                       goto end;
+                       }
                        break;
                }