net: busy-poll: return busypolling status to drivers

NAPI drivers use napi_complete_done() or napi_complete() when
they drained RX ring and right before re-enabling device interrupts.

In busy polling, we can avoid interrupts being delivered since
we are polling RX ring in a controlled loop.

Drivers can chose to use napi_complete_done() return value
to reduce interrupts overhead while busy polling is active.

This is optional, legacy drivers should work fine even
if not updated.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Adam Belay <abelay@google.com>
Cc: Tariq Toukan <tariqt@mellanox.com>
Cc: Yuval Mintz <Yuval.Mintz@cavium.com>
Cc: Ariel Elior <ariel.elior@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -463,16 +463,17 @@ static inline bool napi_reschedule(struct napi_struct *napi)
 	return false;
 }
 
-void __napi_complete(struct napi_struct *n);
-void napi_complete_done(struct napi_struct *n, int work_done);
+bool __napi_complete(struct napi_struct *n);
+bool napi_complete_done(struct napi_struct *n, int work_done);
 /**
  *	napi_complete - NAPI processing complete
  *	@n: NAPI context
  *
  * Mark NAPI processing as complete.
  * Consider using napi_complete_done() instead.
+ * Return false if device should avoid rearming interrupts.
  */
-static inline void napi_complete(struct napi_struct *n)
+static inline bool napi_complete(struct napi_struct *n)
 {
 	return napi_complete_done(n, 0);
 }

net/core/dev.c

@@ -4898,7 +4898,7 @@ void __napi_schedule_irqoff(struct napi_struct *n)
 }
 EXPORT_SYMBOL(__napi_schedule_irqoff);
 
-void __napi_complete(struct napi_struct *n)
+bool __napi_complete(struct napi_struct *n)
 {
 	BUG_ON(!test_bit(NAPI_STATE_SCHED, &n->state));
 
@@ -4906,15 +4906,16 @@ void __napi_complete(struct napi_struct *n)
 	 * napi_complete_done().
 	 */
 	if (unlikely(test_bit(NAPI_STATE_IN_BUSY_POLL, &n->state)))
-		return;
+		return false;
 
 	list_del_init(&n->poll_list);
 	smp_mb__before_atomic();
 	clear_bit(NAPI_STATE_SCHED, &n->state);
+	return true;
 }
 EXPORT_SYMBOL(__napi_complete);
 
-void napi_complete_done(struct napi_struct *n, int work_done)
+bool napi_complete_done(struct napi_struct *n, int work_done)
 {
 	unsigned long flags;
 
@@ -4926,7 +4927,7 @@ void napi_complete_done(struct napi_struct *n, int work_done)
 	 */
 	if (unlikely(n->state & (NAPIF_STATE_NPSVC |
 				 NAPIF_STATE_IN_BUSY_POLL)))
-		return;
+		return false;
 
 	if (n->gro_list) {
 		unsigned long timeout = 0;
@@ -4948,6 +4949,7 @@ void napi_complete_done(struct napi_struct *n, int work_done)
 		__napi_complete(n);
 		local_irq_restore(flags);
 	}
+	return true;
 }
 EXPORT_SYMBOL(napi_complete_done);