net: Switch from per-iface tx thread to a unique k_poll triggered one

Now that k_poll landed in the kernel, it's worth using it to save
memory and reduce the number of threads at runtime.

Such switch has been first done in bluetooth (see hci_core.c and conn.c
in subsys/bluetooth/host). Since network interfaces kind of follows the
same design for sending data, it was then easy to copy the same change as
in bluetooth.

Change-Id: I7f9734b88ac818284bbabaedc946b4765b905ebb
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>

include/linker/common-ram.ld

@@ -134,10 +134,18 @@
 	{
 		__net_if_start = .;
 		*(".net_if.*")
-		KEEP(*(SORT_BY_NAME(".net_if*")))
+		KEEP(*(SORT_BY_NAME(".net_if.*")))
 		__net_if_end = .;
 	} GROUP_DATA_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
 
+	SECTION_DATA_PROLOGUE(net_if_event, (OPTIONAL),)
+	{
+		__net_if_event_start = .;
+		*(".net_if_event.*")
+		KEEP(*(SORT_BY_NAME(".net_if_event.*")))
+		__net_if_event_end = .;
+	} GROUP_DATA_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
+
 #if defined(CONFIG_NET_SHELL)
 	SECTION_DATA_PROLOGUE(net_stack, (OPTIONAL),)
 	{

include/net/net_if.h

@@ -203,12 +203,6 @@ struct net_if {
 	/** Queue for outgoing packets from apps */
 	struct k_fifo tx_queue;
 
-	/** Stack for the TX thread tied to this interface */
-#ifndef CONFIG_NET_TX_STACK_SIZE
-#define CONFIG_NET_TX_STACK_SIZE 1024
-#endif
-	NET_STACK_DEFINE_EMBEDDED(tx_stack, CONFIG_NET_TX_STACK_SIZE);
-
 #if defined(CONFIG_NET_IPV6)
 #define NET_IF_MAX_IPV6_ADDR CONFIG_NET_IF_UNICAST_IPV6_ADDR_COUNT
 #define NET_IF_MAX_IPV6_MADDR CONFIG_NET_IF_MCAST_IPV6_ADDR_COUNT
@@ -1190,6 +1184,9 @@ struct net_if_api {
 #endif
 
 #define NET_IF_GET_NAME(dev_name, sfx) (__net_if_##dev_name##_##sfx)
+#define NET_IF_EVENT_GET_NAME(dev_name, sfx)	\
+	(__net_if_event_##dev_name##_##sfx)
+
 #define NET_IF_GET(dev_name, sfx)					\
 	((struct net_if *)&NET_IF_GET_NAME(dev_name, sfx))
 
@@ -1202,12 +1199,9 @@ struct net_if_api {
 		.mtu = _mtu,						\
 		NET_IF_DHCPV4_INIT					\
 	};								\
-	NET_STACK_INFO_ADDR(TX,						\
+	static struct k_poll_event					\
-			    dev_name,					\
+	(NET_IF_EVENT_GET_NAME(dev_name, sfx)) __used			\
-			    CONFIG_NET_TX_STACK_SIZE,			\
+		__attribute__((__section__(".net_if_event.data"))) = {}
-			    CONFIG_NET_TX_STACK_SIZE,			\
-			    NET_IF_GET(dev_name, sfx)->tx_stack,	\
-			    sfx)
 
 
 /* Network device initialization macros */

scripts/sanitycheck

@@ -470,7 +470,7 @@ class SizeCalculator:
 		   "_k_sem_area", "_k_mutex_area", "_k_alert_area",
 		   "_k_fifo_area", "_k_lifo_area", "_k_stack_area",
 		   "_k_msgq_area", "_k_mbox_area", "_k_pipe_area",
-                   "net_if", "net_stack", "net_l2_data",
+                   "net_if", "net_if_event", "net_stack", "net_l2_data",
                    "_k_queue_area"]
     # These get copied into RAM only on non-XIP
     ro_sections = ["text", "ctors", "init_array", "reset",

subsys/net/Kconfig

@@ -61,6 +61,7 @@ config NET_BUF_POOL_USAGE
 config  NETWORKING
 	bool "Link layer and IP networking support"
 	select NET_BUF
+	select POLL
 	select RANDOM_GENERATOR
 	default n
 	help

subsys/net/ip/net_if.c

@@ -33,12 +33,18 @@
 extern struct net_if __net_if_start[];
 extern struct net_if __net_if_end[];
 
+extern struct k_poll_event __net_if_event_start[];
+extern struct k_poll_event __net_if_event_stop[];
+
 static struct net_if_router routers[CONFIG_NET_MAX_ROUTERS];
 
 /* We keep track of the link callbacks in this list.
  */
 static sys_slist_t link_callbacks;
 
+NET_STACK_DEFINE(TX, tx_stack, CONFIG_NET_TX_STACK_SIZE,
+		 CONFIG_NET_TX_STACK_SIZE);
+
 #if defined(CONFIG_NET_DEBUG_IF)
 #define debug_check_packet(buf)						    \
 	{								    \
@@ -67,17 +73,23 @@ static inline void net_context_send_cb(struct net_context *context,
 #endif
 }
 
-static void iface_send_data(struct net_if *iface, struct net_buf *buf)
+static bool net_if_tx(struct net_if *iface)
 {
 	const struct net_if_api *api = iface->dev->driver_api;
 	struct net_linkaddr *dst;
 	struct net_context *context;
+	struct net_buf *buf;
 	void *context_token;
 	int status;
 #if defined(CONFIG_NET_STATISTICS)
 	size_t pkt_len;
 #endif
 
+	buf = net_buf_get(&iface->tx_queue, K_NO_WAIT);
+	if (!buf) {
+		return false;
+	}
+
 	debug_check_packet(buf);
 
 	dst = net_nbuf_ll_dst(buf);
@@ -109,6 +121,8 @@ static void iface_send_data(struct net_if *iface, struct net_buf *buf)
 	}
 
 	net_if_call_link_cb(iface, dst, status);
+
+	return true;
 }
 
 static void net_if_flush_tx(struct net_if *iface)
@@ -126,56 +140,88 @@ static void net_if_flush_tx(struct net_if *iface)
 	k_yield();
 
 	while (1) {
-		struct net_buf *buf;
+		if (!net_if_tx(iface)) {
-
-		buf = net_buf_get(&iface->tx_queue, K_NO_WAIT);
-		if (!buf) {
 			break;
 		}
-
-		iface_send_data(iface, buf);
 	}
 }
 
-static void net_if_tx_thread(struct net_if *iface)
+static void net_if_process_events(struct k_poll_event *event, int ev_count)
 {
-	const struct net_if_api *api = iface->dev->driver_api;
+	for (; ev_count; event++, ev_count--) {
+		switch (event->state) {
+		case K_POLL_STATE_SIGNALED:
+			break;
+		case K_POLL_STATE_FIFO_DATA_AVAILABLE:
+		{
+			struct net_if *iface;
 
-	NET_ASSERT(api && api->init && api->send);
+			iface = CONTAINER_OF(event->fifo, struct net_if,
+					     tx_queue);
+			net_if_tx(iface);
 
-	NET_DBG("Starting TX thread (stack %zu bytes) for driver %p queue %p",
+			break;
-		sizeof(iface->tx_stack), api, &iface->tx_queue);
+		}
+		case K_POLL_STATE_NOT_READY:
+			break;
+		default:
+			break;
+		}
+	}
+}
 
-	api->init(iface);
+static int net_if_prepare_events(void)
-	/* Attempt to bring the interface up */
+{
-	net_if_up(iface);
+	struct net_if *iface;
+	int ev_count = 0;
+
+	for (iface = __net_if_start; iface != __net_if_end; iface++) {
+		if (!atomic_test_bit(iface->flags, NET_IF_UP)) {
+			continue;
+		}
+
+		k_poll_event_init(&__net_if_event_start[ev_count],
+				  K_POLL_TYPE_FIFO_DATA_AVAILABLE,
+				  K_POLL_MODE_NOTIFY_ONLY,
+				  &iface->tx_queue);
+		ev_count++;
+	}
+
+	return ev_count;
+}
+
+static void net_if_tx_thread(void)
+{
+	NET_DBG("Starting TX thread (stack %zu bytes)",
+		CONFIG_NET_TX_STACK_SIZE);
 
 	while (1) {
-		struct net_buf *buf;
+		int ev_count;
 
-		/* Get next packet from application - wait if necessary */
+		ev_count = net_if_prepare_events();
-		buf = net_buf_get(&iface->tx_queue, K_FOREVER);
 
-		iface_send_data(iface, buf);
+		k_poll(__net_if_event_start, ev_count, K_FOREVER);
 
-		net_analyze_stack("TX thread", iface->tx_stack,
+		net_if_process_events(__net_if_event_start, ev_count);
-				  sizeof(iface->tx_stack));
-		net_nbuf_print();
 
 		k_yield();
 	}
 }
 
-static inline void init_tx_queue(struct net_if *iface)
+static inline void init_iface(struct net_if *iface)
 {
+	const struct net_if_api *api = iface->dev->driver_api;
+
+	NET_ASSERT(api && api->init && api->send);
+
 	NET_DBG("On iface %p", iface);
 
 	k_fifo_init(&iface->tx_queue);
 
-	k_thread_spawn(iface->tx_stack, sizeof(iface->tx_stack),
+	api->init(iface);
-		       (k_thread_entry_t)net_if_tx_thread,
+
-		       iface, NULL, NULL, K_PRIO_COOP(7),
+	/* Attempt to bring the interface up */
-		       K_ESSENTIAL, K_NO_WAIT);
+	net_if_up(iface);
 }
 
 enum net_verdict net_if_send_data(struct net_if *iface, struct net_buf *buf)
@@ -1561,7 +1607,7 @@ void net_if_init(void)
 	NET_DBG("");
 
 	for (iface = __net_if_start; iface != __net_if_end; iface++) {
-		init_tx_queue(iface);
+		init_iface(iface);
 
 #if defined(CONFIG_NET_IPV4)
 		iface->ttl = CONFIG_NET_INITIAL_TTL;
@@ -1575,6 +1621,11 @@ void net_if_init(void)
 #endif
 	}
 
+	k_thread_spawn(tx_stack, sizeof(tx_stack),
+		       (k_thread_entry_t)net_if_tx_thread,
+		       NULL, NULL, NULL, K_PRIO_COOP(7),
+		       K_ESSENTIAL, K_NO_WAIT);
+
 	/* RPL init must be done after the network interface is up
 	 * as the RPL code wants to add multicast address to interface.
 	 */

subsys/net/ip/net_shell.c

@@ -76,29 +76,6 @@ static inline const char *addrstate2str(enum net_addr_state addr_state)
 	return "<invalid state>";
 }
 
-static void tx_stack(struct net_if *iface, unsigned char *stack,
-		     size_t stack_size)
-{
-	ARG_UNUSED(iface);
-
-#if defined(CONFIG_INIT_STACKS)
-	unsigned int stack_offset, pcnt, unused;
-
-	net_analyze_stack_get_values(stack, stack_size,
-				     &stack_offset, &pcnt, &unused);
-
-	printk("TX stack size %zu/%zu bytes unused %u usage %zu/%zu (%u %%)\n",
-	       stack_size,
-	       stack_size + stack_offset, unused,
-	       stack_size - unused, stack_size, pcnt);
-#else
-	ARG_UNUSED(stack_size);
-	ARG_UNUSED(stack);
-
-	printk("TX stack usage not available.\n");
-#endif
-}
-
 static void iface_cb(struct net_if *iface, void *user_data)
 {
 #if defined(CONFIG_NET_IPV6)
@@ -114,8 +91,6 @@ static void iface_cb(struct net_if *iface, void *user_data)
 	printk("Interface %p\n", iface);
 	printk("====================\n");
 
-	tx_stack(iface, iface->tx_stack, CONFIG_NET_TX_STACK_SIZE);
-
 	printk("Link addr : %s\n", net_sprint_ll_addr(iface->link_addr.addr,
 						      iface->link_addr.len));
 	printk("MTU       : %d\n", iface->mtu);