Merge branch 'gro-micro-optimize-dev_gro_receive'

Alexander Lobakin says:

====================
gro: micro-optimize dev_gro_receive()

This random series addresses some of suboptimal constructions used
in the main GRO entry point.
The main body is gro_list_prepare() simplification and pointer usage
optimization in dev_gro_receive() itself. Being mostly cosmetic, it
gives like +10 Mbps on my setup to both TCP and UDP (both single- and
multi-flow).

Since v1 [0]:
 - drop the replacement of bucket index calculation with
   reciprocal_scale() since it makes absolutely no sense (Eric);
 - improve stack usage in dev_gro_receive() (Eric);
 - reverse the order of patches to avoid changes superseding.

[0] https://lore.kernel.org/netdev/20210312162127.239795-1-alobakin@pm.me
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -5858,15 +5858,13 @@ void napi_gro_flush(struct napi_struct *napi, bool flush_old)
 }
 EXPORT_SYMBOL(napi_gro_flush);
 
-static struct list_head *gro_list_prepare(struct napi_struct *napi,
-					  struct sk_buff *skb)
+static void gro_list_prepare(const struct list_head *head,
+			     const struct sk_buff *skb)
 {
 	unsigned int maclen = skb->dev->hard_header_len;
 	u32 hash = skb_get_hash_raw(skb);
-	struct list_head *head;
 	struct sk_buff *p;
 
-	head = &napi->gro_hash[hash & (GRO_HASH_BUCKETS - 1)].list;
 	list_for_each_entry(p, head, list) {
 		unsigned long diffs;
 
@@ -5892,8 +5890,6 @@ static struct list_head *gro_list_prepare(struct napi_struct *napi,
 				       maclen);
 		NAPI_GRO_CB(p)->same_flow = !diffs;
 	}
-
-	return head;
 }
 
 static void skb_gro_reset_offset(struct sk_buff *skb)
@@ -5956,11 +5952,11 @@ 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 hash = skb_get_hash_raw(skb) & (GRO_HASH_BUCKETS - 1);
+	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;
-	struct list_head *gro_head;
 	struct sk_buff *pp = NULL;
 	enum gro_result ret;
 	int same_flow;
@@ -5969,7 +5965,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	if (netif_elide_gro(skb->dev))
 		goto normal;
 
-	gro_head = gro_list_prepare(napi, skb);
+	gro_list_prepare(&gro_list->list, skb);
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(ptype, head, list) {
@@ -6005,7 +6001,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 
 		pp = INDIRECT_CALL_INET(ptype->callbacks.gro_receive,
 					ipv6_gro_receive, inet_gro_receive,
-					gro_head, skb);
+					&gro_list->list, skb);
 		break;
 	}
 	rcu_read_unlock();
@@ -6024,7 +6020,7 @@ 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[hash].count--;
+		gro_list->count--;
 	}
 
 	if (same_flow)
@@ -6033,16 +6029,16 @@ 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[hash].count >= MAX_GRO_SKBS)) {
-		gro_flush_oldest(napi, gro_head);
-	} else {
-		napi->gro_hash[hash].count++;
-	}
+	if (unlikely(gro_list->count >= MAX_GRO_SKBS))
+		gro_flush_oldest(napi, &gro_list->list);
+	else
+		gro_list->count++;
+
 	NAPI_GRO_CB(skb)->count = 1;
 	NAPI_GRO_CB(skb)->age = jiffies;
 	NAPI_GRO_CB(skb)->last = skb;
 	skb_shinfo(skb)->gso_size = skb_gro_len(skb);
-	list_add(&skb->list, gro_head);
+	list_add(&skb->list, &gro_list->list);
 	ret = GRO_HELD;
 
 pull:
@@ -6050,11 +6046,11 @@ 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[hash].count) {
-		if (!test_bit(hash, &napi->gro_bitmask))
-			__set_bit(hash, &napi->gro_bitmask);
-	} else if (test_bit(hash, &napi->gro_bitmask)) {
-		__clear_bit(hash, &napi->gro_bitmask);
+	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)) {
+		__clear_bit(bucket, &napi->gro_bitmask);
 	}
 
 	return ret;