Merge branch 'net-napi-addition-of-napi_defer_hard_irqs'

Eric Dumazet says:

====================
net: napi: addition of napi_defer_hard_irqs

This patch series augments gro_glush_timeout feature with napi_defer_hard_irqs

As extensively described in first patch changelog, this can suppresss
the chit-chat traffic between NIC and host to signal interrupts and re-arming
them, since this can be an issue on high speed NIC with many queues.

The last patch in this series converts mlx4 TX completion to
napi_complete_done(), to enable this new mechanism.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/en_rx.c

@@ -946,7 +946,7 @@ int mlx4_en_poll_rx_cq(struct napi_struct *napi, int budget)
 		xdp_tx_cq = priv->tx_cq[TX_XDP][cq->ring];
 		if (xdp_tx_cq->xdp_busy) {
 			clean_complete = mlx4_en_process_tx_cq(dev, xdp_tx_cq,
-							       budget);
+							       budget) < budget;
 			xdp_tx_cq->xdp_busy = !clean_complete;
 		}
 	}

drivers/net/ethernet/mellanox/mlx4/en_tx.c

@@ -382,8 +382,8 @@ int mlx4_en_free_tx_buf(struct net_device *dev, struct mlx4_en_tx_ring *ring)
 	return cnt;
 }
 
-bool mlx4_en_process_tx_cq(struct net_device *dev,
-			   struct mlx4_en_cq *cq, int napi_budget)
+int mlx4_en_process_tx_cq(struct net_device *dev,
+			  struct mlx4_en_cq *cq, int napi_budget)
 {
 	struct mlx4_en_priv *priv = netdev_priv(dev);
 	struct mlx4_cq *mcq = &cq->mcq;
@@ -405,7 +405,7 @@ bool mlx4_en_process_tx_cq(struct net_device *dev,
 	u32 ring_cons;
 
 	if (unlikely(!priv->port_up))
-		return true;
+		return 0;
 
 	netdev_txq_bql_complete_prefetchw(ring->tx_queue);
 
@@ -480,7 +480,7 @@ bool mlx4_en_process_tx_cq(struct net_device *dev,
 	WRITE_ONCE(ring->cons, ring_cons + txbbs_skipped);
 
 	if (cq->type == TX_XDP)
-		return done < budget;
+		return done;
 
 	netdev_tx_completed_queue(ring->tx_queue, packets, bytes);
 
@@ -492,7 +492,7 @@ bool mlx4_en_process_tx_cq(struct net_device *dev,
 		ring->wake_queue++;
 	}
 
-	return done < budget;
+	return done;
 }
 
 void mlx4_en_tx_irq(struct mlx4_cq *mcq)
@@ -512,14 +512,14 @@ int mlx4_en_poll_tx_cq(struct napi_struct *napi, int budget)
 	struct mlx4_en_cq *cq = container_of(napi, struct mlx4_en_cq, napi);
 	struct net_device *dev = cq->dev;
 	struct mlx4_en_priv *priv = netdev_priv(dev);
-	bool clean_complete;
+	int work_done;
 
-	clean_complete = mlx4_en_process_tx_cq(dev, cq, budget);
-	if (!clean_complete)
+	work_done = mlx4_en_process_tx_cq(dev, cq, budget);
+	if (work_done >= budget)
 		return budget;
 
-	napi_complete(napi);
-	mlx4_en_arm_cq(priv, cq);
+	if (napi_complete_done(napi, work_done))
+		mlx4_en_arm_cq(priv, cq);
 
 	return 0;
 }

drivers/net/ethernet/mellanox/mlx4/mlx4_en.h

@@ -737,8 +737,8 @@ int mlx4_en_process_rx_cq(struct net_device *dev,
 			  int budget);
 int mlx4_en_poll_rx_cq(struct napi_struct *napi, int budget);
 int mlx4_en_poll_tx_cq(struct napi_struct *napi, int budget);
-bool mlx4_en_process_tx_cq(struct net_device *dev,
-			   struct mlx4_en_cq *cq, int napi_budget);
+int mlx4_en_process_tx_cq(struct net_device *dev,
+			  struct mlx4_en_cq *cq, int napi_budget);
 u32 mlx4_en_free_tx_desc(struct mlx4_en_priv *priv,
 			 struct mlx4_en_tx_ring *ring,
 			 int index, u64 timestamp,

include/linux/netdevice.h

@@ -329,6 +329,7 @@ struct napi_struct {
 
 	unsigned long		state;
 	int			weight;
+	int			defer_hard_irqs_count;
 	unsigned long		gro_bitmask;
 	int			(*poll)(struct napi_struct *, int);
 #ifdef CONFIG_NETPOLL
@@ -1995,6 +1996,7 @@ struct net_device {
 
 	struct bpf_prog __rcu	*xdp_prog;
 	unsigned long		gro_flush_timeout;
+	int			napi_defer_hard_irqs;
 	rx_handler_func_t __rcu	*rx_handler;
 	void __rcu		*rx_handler_data;
 

net/core/dev.c

@@ -6227,7 +6227,8 @@ EXPORT_SYMBOL(__napi_schedule_irqoff);
 
 bool napi_complete_done(struct napi_struct *n, int work_done)
 {
-	unsigned long flags, val, new;
+	unsigned long flags, val, new, timeout = 0;
+	bool ret = true;
 
 	/*
 	 * 1) Don't let napi dequeue from the cpu poll list
@@ -6239,20 +6240,23 @@ bool napi_complete_done(struct napi_struct *n, int work_done)
 				 NAPIF_STATE_IN_BUSY_POLL)))
 		return false;
 
+	if (work_done) {
+		if (n->gro_bitmask)
+			timeout = READ_ONCE(n->dev->gro_flush_timeout);
+		n->defer_hard_irqs_count = READ_ONCE(n->dev->napi_defer_hard_irqs);
+	}
+	if (n->defer_hard_irqs_count > 0) {
+		n->defer_hard_irqs_count--;
+		timeout = READ_ONCE(n->dev->gro_flush_timeout);
+		if (timeout)
+			ret = false;
+	}
 	if (n->gro_bitmask) {
-		unsigned long timeout = 0;
-
-		if (work_done)
-			timeout = n->dev->gro_flush_timeout;
-
 		/* When the NAPI instance uses a timeout and keeps postponing
 		 * it, we need to bound somehow the time packets are kept in
 		 * the GRO layer
 		 */
 		napi_gro_flush(n, !!timeout);
-		if (timeout)
-			hrtimer_start(&n->timer, ns_to_ktime(timeout),
-				      HRTIMER_MODE_REL_PINNED);
 	}
 
 	gro_normal_list(n);
@@ -6284,7 +6288,10 @@ bool napi_complete_done(struct napi_struct *n, int work_done)
 		return false;
 	}
 
-	return true;
+	if (timeout)
+		hrtimer_start(&n->timer, ns_to_ktime(timeout),
+			      HRTIMER_MODE_REL_PINNED);
+	return ret;
 }
 EXPORT_SYMBOL(napi_complete_done);
 
@@ -6464,7 +6471,7 @@ static enum hrtimer_restart napi_watchdog(struct hrtimer *timer)
 	/* Note : we use a relaxed variant of napi_schedule_prep() not setting
 	 * NAPI_STATE_MISSED, since we do not react to a device IRQ.
 	 */
-	if (napi->gro_bitmask && !napi_disable_pending(napi) &&
+	if (!napi_disable_pending(napi) &&
 	    !test_and_set_bit(NAPI_STATE_SCHED, &napi->state))
 		__napi_schedule_irqoff(napi);
 

net/core/net-sysfs.c

@@ -367,7 +367,7 @@ NETDEVICE_SHOW_RW(tx_queue_len, fmt_dec);
 
 static int change_gro_flush_timeout(struct net_device *dev, unsigned long val)
 {
-	dev->gro_flush_timeout = val;
+	WRITE_ONCE(dev->gro_flush_timeout, val);
 	return 0;
 }
 
@@ -382,6 +382,23 @@ static ssize_t gro_flush_timeout_store(struct device *dev,
 }
 NETDEVICE_SHOW_RW(gro_flush_timeout, fmt_ulong);
 
+static int change_napi_defer_hard_irqs(struct net_device *dev, unsigned long val)
+{
+	WRITE_ONCE(dev->napi_defer_hard_irqs, val);
+	return 0;
+}
+
+static ssize_t napi_defer_hard_irqs_store(struct device *dev,
+					  struct device_attribute *attr,
+					  const char *buf, size_t len)
+{
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
+	return netdev_store(dev, attr, buf, len, change_napi_defer_hard_irqs);
+}
+NETDEVICE_SHOW_RW(napi_defer_hard_irqs, fmt_dec);
+
 static ssize_t ifalias_store(struct device *dev, struct device_attribute *attr,
 			     const char *buf, size_t len)
 {
@@ -545,6 +562,7 @@ static struct attribute *net_class_attrs[] __ro_after_init = {
 	&dev_attr_flags.attr,
 	&dev_attr_tx_queue_len.attr,
 	&dev_attr_gro_flush_timeout.attr,
+	&dev_attr_napi_defer_hard_irqs.attr,
 	&dev_attr_phys_port_id.attr,
 	&dev_attr_phys_port_name.attr,
 	&dev_attr_phys_switch_id.attr,