netdev - [PATCH net-next 2/4] gro: don't dereference napi->gro_hash[x] multiple times in dev_gro

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Message-ID: <20210312162127.239795-3-alobakin@pm.me>
Date:   Fri, 12 Mar 2021 16:21:58 +0000
From:   Alexander Lobakin <alobakin@...me>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        Alexander Lobakin <alobakin@...me>,
        Eric Dumazet <edumazet@...gle.com>,
        Wei Wang <weiwan@...gle.com>,
        Cong Wang <cong.wang@...edance.com>,
        Taehee Yoo <ap420073@...il.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH net-next 2/4] gro: don't dereference napi->gro_hash[x] multiple times in dev_gro_receive()

GRO bucket index doesn't change through the entire function.
Store a pointer to the corresponding bucket on stack once and use
it later instead of dereferencing again and again.

Signed-off-by: Alexander Lobakin <alobakin@...me>
---
 net/core/dev.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index adc42ba7ffd8..ee124aecb8a2 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5957,6 +5957,7 @@ static void gro_flush_oldest(struct napi_struct *napi, struct list_head *head)
 static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
 {
 	u32 bucket = skb_get_hash_raw(skb) & (GRO_HASH_BUCKETS - 1);
+	struct gro_list *gro_list = &napi->gro_hash[bucket];
 	struct list_head *head = &offload_base;
 	struct packet_offload *ptype;
 	__be16 type = skb->protocol;
@@ -6024,7 +6025,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	if (pp) {
 		skb_list_del_init(pp);
 		napi_gro_complete(napi, pp);
-		napi->gro_hash[bucket].count--;
+		gro_list->count--;
 	}

 	if (same_flow)
@@ -6033,10 +6034,10 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	if (NAPI_GRO_CB(skb)->flush)
 		goto normal;

-	if (unlikely(napi->gro_hash[bucket].count >= MAX_GRO_SKBS)) {
+	if (unlikely(gro_list->count >= MAX_GRO_SKBS)) {
 		gro_flush_oldest(napi, gro_head);
 	} else {
-		napi->gro_hash[bucket].count++;
+		gro_list->count++;
 	}
 	NAPI_GRO_CB(skb)->count = 1;
 	NAPI_GRO_CB(skb)->age = jiffies;
@@ -6050,7 +6051,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	if (grow > 0)
 		gro_pull_from_frag0(skb, grow);
 ok:
-	if (napi->gro_hash[bucket].count) {
+	if (gro_list->count) {
 		if (!test_bit(bucket, &napi->gro_bitmask))
 			__set_bit(bucket, &napi->gro_bitmask);
 	} else if (test_bit(bucket, &napi->gro_bitmask)) {
--
2.30.2