net: introduce struct net_hotdata

Instead of spreading networking critical fields
all over the places, add a custom net_hotdata
structure so that we can precisely control its layout.

In this first patch, move :

- gro_normal_batch used in rx (GRO stack)
- offload_base used in rx and tx (GRO and TSO stacks)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240306160031.874438-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/netdevice.h

@@ -4796,7 +4796,6 @@ void dev_get_tstats64(struct net_device *dev, struct rtnl_link_stats64 *s);
 extern int		netdev_max_backlog;
 extern int		dev_rx_weight;
 extern int		dev_tx_weight;
-extern int		gro_normal_batch;
 
 enum {
 	NESTED_SYNC_IMM_BIT,

include/net/gro.h

@@ -9,6 +9,7 @@
 #include <net/ip6_checksum.h>
 #include <linux/skbuff.h>
 #include <net/udp.h>
+#include <net/hotdata.h>
 
 struct napi_gro_cb {
 	union {
@@ -446,7 +447,7 @@ static inline void gro_normal_one(struct napi_struct *napi, struct sk_buff *skb,
 {
 	list_add_tail(&skb->list, &napi->rx_list);
 	napi->rx_count += segs;
-	if (napi->rx_count >= READ_ONCE(gro_normal_batch))
+	if (napi->rx_count >= READ_ONCE(net_hotdata.gro_normal_batch))
 		gro_normal_list(napi);
 }
 
@@ -493,6 +494,4 @@ static inline void inet6_get_iif_sdif(const struct sk_buff *skb, int *iif, int *
 #endif
 }
 
-extern struct list_head offload_base;
-
 #endif /* _NET_IPV6_GRO_H */

include/net/hotdata.h

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _NET_HOTDATA_H
+#define _NET_HOTDATA_H
+
+#include <linux/types.h>
+
+/* Read mostly data used in network fast paths. */
+struct net_hotdata {
+	struct list_head	offload_base;
+	int			gro_normal_batch;
+};
+
+extern struct net_hotdata net_hotdata;
+
+#endif /* _NET_HOTDATA_H */

net/core/Makefile

@@ -18,6 +18,7 @@ obj-y		     += dev.o dev_addr_lists.o dst.o netevent.o \
 obj-$(CONFIG_NETDEV_ADDR_LIST_TEST) += dev_addr_lists_test.o
 
 obj-y += net-sysfs.o
+obj-y += hotdata.o
 obj-$(CONFIG_PAGE_POOL) += page_pool.o page_pool_user.o
 obj-$(CONFIG_PROC_FS) += net-procfs.o
 obj-$(CONFIG_NET_PKTGEN) += pktgen.o

net/core/gro.c

@@ -10,9 +10,6 @@
 #define GRO_MAX_HEAD (MAX_HEADER + 128)
 
 static DEFINE_SPINLOCK(offload_lock);
-struct list_head offload_base __read_mostly = LIST_HEAD_INIT(offload_base);
-/* Maximum number of GRO_NORMAL skbs to batch up for list-RX */
-int gro_normal_batch __read_mostly = 8;
 
 /**
  *	dev_add_offload - register offload handlers
@@ -31,7 +28,7 @@ void dev_add_offload(struct packet_offload *po)
 	struct packet_offload *elem;
 
 	spin_lock(&offload_lock);
-	list_for_each_entry(elem, &offload_base, list) {
+	list_for_each_entry(elem, &net_hotdata.offload_base, list) {
 		if (po->priority < elem->priority)
 			break;
 	}
@@ -55,7 +52,7 @@ EXPORT_SYMBOL(dev_add_offload);
  */
 static void __dev_remove_offload(struct packet_offload *po)
 {
-	struct list_head *head = &offload_base;
+	struct list_head *head = &net_hotdata.offload_base;
 	struct packet_offload *po1;
 
 	spin_lock(&offload_lock);
@@ -235,9 +232,9 @@ done:
 
 static void napi_gro_complete(struct napi_struct *napi, struct sk_buff *skb)
 {
+	struct list_head *head = &net_hotdata.offload_base;
 	struct packet_offload *ptype;
 	__be16 type = skb->protocol;
-	struct list_head *head = &offload_base;
 	int err = -ENOENT;
 
 	BUILD_BUG_ON(sizeof(struct napi_gro_cb) > sizeof(skb->cb));
@@ -444,7 +441,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 {
 	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 list_head *head = &net_hotdata.offload_base;
 	struct packet_offload *ptype;
 	__be16 type = skb->protocol;
 	struct sk_buff *pp = NULL;
@@ -550,7 +547,7 @@ normal:
 
 struct packet_offload *gro_find_receive_by_type(__be16 type)
 {
-	struct list_head *offload_head = &offload_base;
+	struct list_head *offload_head = &net_hotdata.offload_base;
 	struct packet_offload *ptype;
 
 	list_for_each_entry_rcu(ptype, offload_head, list) {
@@ -564,7 +561,7 @@ EXPORT_SYMBOL(gro_find_receive_by_type);
 
 struct packet_offload *gro_find_complete_by_type(__be16 type)
 {
-	struct list_head *offload_head = &offload_base;
+	struct list_head *offload_head = &net_hotdata.offload_base;
 	struct packet_offload *ptype;
 
 	list_for_each_entry_rcu(ptype, offload_head, list) {

net/core/gso.c

@@ -17,7 +17,7 @@ struct sk_buff *skb_eth_gso_segment(struct sk_buff *skb,
 	struct packet_offload *ptype;
 
 	rcu_read_lock();
-	list_for_each_entry_rcu(ptype, &offload_base, list) {
+	list_for_each_entry_rcu(ptype, &net_hotdata.offload_base, list) {
 		if (ptype->type == type && ptype->callbacks.gso_segment) {
 			segs = ptype->callbacks.gso_segment(skb, features);
 			break;
@@ -48,7 +48,7 @@ struct sk_buff *skb_mac_gso_segment(struct sk_buff *skb,
 	__skb_pull(skb, vlan_depth);
 
 	rcu_read_lock();
-	list_for_each_entry_rcu(ptype, &offload_base, list) {
+	list_for_each_entry_rcu(ptype, &net_hotdata.offload_base, list) {
 		if (ptype->type == type && ptype->callbacks.gso_segment) {
 			segs = ptype->callbacks.gso_segment(skb, features);
 			break;

net/core/hotdata.c

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <net/hotdata.h>
+#include <linux/cache.h>
+#include <linux/list.h>
+
+struct net_hotdata net_hotdata __cacheline_aligned = {
+	.offload_base = LIST_HEAD_INIT(net_hotdata.offload_base),
+	.gro_normal_batch = 8,
+};

net/core/sysctl_net_core.c

@@ -23,6 +23,7 @@
 #include <net/net_ratelimit.h>
 #include <net/busy_poll.h>
 #include <net/pkt_sched.h>
+#include <net/hotdata.h>
 
 #include "dev.h"
 
@@ -632,7 +633,7 @@ static struct ctl_table net_core_table[] = {
 	},
 	{
 		.procname	= "gro_normal_batch",
-		.data		= &gro_normal_batch,
+		.data		= &net_hotdata.gro_normal_batch,
 		.maxlen		= sizeof(unsigned int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,