netdev - [PATCH v4 net-next 9/9] net: don't bother calling list RX functions on empty lists

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Date:   Mon, 2 Jul 2018 16:14:44 +0100
From:   Edward Cree <ecree@...arflare.com>
To:     <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>
Subject: [PATCH v4 net-next 9/9] net: don't bother calling list RX functions
 on empty lists

Generally the check should be very cheap, as the sk_buff_head is in cache.

Signed-off-by: Edward Cree <ecree@...arflare.com>
---
 net/core/dev.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 4c5ebfab9bc8..d6084b0cd9ce 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4773,7 +4773,8 @@ static void __netif_receive_skb_list(struct list_head *head)
 
 			/* Handle the previous sublist */
 			list_cut_before(&sublist, head, &skb->list);
-			__netif_receive_skb_list_core(&sublist, pfmemalloc);
+			if (!list_empty(&sublist))
+				__netif_receive_skb_list_core(&sublist, pfmemalloc);
 			pfmemalloc = !pfmemalloc;
 			/* See comments in __netif_receive_skb */
 			if (pfmemalloc)
@@ -4783,7 +4784,8 @@ static void __netif_receive_skb_list(struct list_head *head)
 		}
 	}
 	/* Handle the remaining sublist */
-	__netif_receive_skb_list_core(head, pfmemalloc);
+	if (!list_empty(head))
+		__netif_receive_skb_list_core(head, pfmemalloc);
 	/* Restore pflags */
 	if (pfmemalloc)
 		memalloc_noreclaim_restore(noreclaim_flag);
@@ -4944,6 +4946,8 @@ void netif_receive_skb_list(struct list_head *head)
 {
 	struct sk_buff *skb;
 
+	if (list_empty(head))
+		return;
 	list_for_each_entry(skb, head, list)
 		trace_netif_receive_skb_list_entry(skb);
 	netif_receive_skb_list_internal(head);