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Date:   Fri, 12 Mar 2021 16:21:58 +0000
To:     "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>
From:   Alexander Lobakin <alobakin@pm.me>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andriin@fb.com>,
        Alexander Lobakin <alobakin@pm.me>,
        Eric Dumazet <edumazet@google.com>,
        Wei Wang <weiwan@google.com>,
        Cong Wang <cong.wang@bytedance.com>,
        Taehee Yoo <ap420073@gmail.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Reply-To: Alexander Lobakin <alobakin@pm.me>
Subject: [PATCH net-next 2/4] gro: don't dereference napi->gro_hash[x] multiple times in dev_gro_receive()
Message-ID: <20210312162127.239795-3-alobakin@pm.me>
In-Reply-To: <20210312162127.239795-1-alobakin@pm.me>
References: <20210312162127.239795-1-alobakin@pm.me>
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Precedence: bulk

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@pm.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)
 {
 =09u32 bucket =3D skb_get_hash_raw(skb) & (GRO_HASH_BUCKETS - 1);
+=09struct gro_list *gro_list =3D &napi->gro_hash[bucket];
 =09struct list_head *head =3D &offload_base;
 =09struct packet_offload *ptype;
 =09__be16 type =3D skb->protocol;
@@ -6024,7 +6025,7 @@ static enum gro_result dev_gro_receive(struct napi_st=
ruct *napi, struct sk_buff
 =09if (pp) {
 =09=09skb_list_del_init(pp);
 =09=09napi_gro_complete(napi, pp);
-=09=09napi->gro_hash[bucket].count--;
+=09=09gro_list->count--;
 =09}

 =09if (same_flow)
@@ -6033,10 +6034,10 @@ static enum gro_result dev_gro_receive(struct napi_=
struct *napi, struct sk_buff
 =09if (NAPI_GRO_CB(skb)->flush)
 =09=09goto normal;

-=09if (unlikely(napi->gro_hash[bucket].count >=3D MAX_GRO_SKBS)) {
+=09if (unlikely(gro_list->count >=3D MAX_GRO_SKBS)) {
 =09=09gro_flush_oldest(napi, gro_head);
 =09} else {
-=09=09napi->gro_hash[bucket].count++;
+=09=09gro_list->count++;
 =09}
 =09NAPI_GRO_CB(skb)->count =3D 1;
 =09NAPI_GRO_CB(skb)->age =3D jiffies;
@@ -6050,7 +6051,7 @@ static enum gro_result dev_gro_receive(struct napi_st=
ruct *napi, struct sk_buff
 =09if (grow > 0)
 =09=09gro_pull_from_frag0(skb, grow);
 ok:
-=09if (napi->gro_hash[bucket].count) {
+=09if (gro_list->count) {
 =09=09if (!test_bit(bucket, &napi->gro_bitmask))
 =09=09=09__set_bit(bucket, &napi->gro_bitmask);
 =09} else if (test_bit(bucket, &napi->gro_bitmask)) {
--
2.30.2