Commit 17c84cb4 authored by Maxim Mikityanskiy's avatar Maxim Mikityanskiy Committed by Saeed Mahameed
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net/mlx5e: Sync txq2sq updates with mlx5e_xmit for HTB queues 



This commit makes necessary changes to guarantee that txq2sq remains
stable while mlx5e_xmit is running. Proper synchronization is added for
HTB TX queues.

All updates to txq2sq are performed while the corresponding queue is
disabled (i.e. mlx5e_xmit doesn't run on that queue). smp_wmb after each
change guarantees that mlx5e_xmit can see the updated value after the
queue is enabled. Comments explaining this mechanism are added to
mlx5e_xmit.

When an HTB SQ can be deleted (after deleting an HTB node), synchronize
with RCU to wait for mlx5e_select_queue to finish and stop selecting
that queue, before we re-enable it to avoid TX timeout watchdog alarms.

Signed-off-by: default avatarMaxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: default avatarTariq Toukan <tariqt@nvidia.com>
Signed-off-by: default avatarSaeed Mahameed <saeedm@nvidia.com>
parent 6ce204ea

drivers/net/ethernet/mellanox/mlx5/core/en/qos.c

+20 −4
Original line number Diff line number Diff line
@@ -50,7 +50,6 @@ static int mlx5e_find_unused_qos_qid(struct mlx5e_priv *priv) 


struct mlx5e_qos_node {

	struct hlist_node hnode;

	struct rcu_head rcu;

	struct mlx5e_qos_node *parent;

	u64 rate;

	u32 bw_share;
@@ -132,7 +131,11 @@ static void mlx5e_sw_node_delete(struct mlx5e_priv *priv, struct mlx5e_qos_node 
		__clear_bit(node->qid, priv->htb.qos_used_qids);

		mlx5e_update_tx_netdev_queues(priv);

	}

	kfree_rcu(node, rcu);

	/* Make sure this qid is no longer selected by mlx5e_select_queue, so

	 * that mlx5e_reactivate_qos_sq can safely restart the netdev TX queue.

	 */

	synchronize_net();

	kfree(node);

}



/* TX datapath API */
@@ -273,10 +276,18 @@ static int mlx5e_open_qos_sq(struct mlx5e_priv *priv, struct mlx5e_channels *chs 
static void mlx5e_activate_qos_sq(struct mlx5e_priv *priv, struct mlx5e_qos_node *node)

{

	struct mlx5e_txqsq *sq;

	u16 qid;



	sq = mlx5e_get_qos_sq(priv, node->qid);



	WRITE_ONCE(priv->txq2sq[mlx5e_qid_from_qos(&priv->channels, node->qid)], sq);

	qid = mlx5e_qid_from_qos(&priv->channels, node->qid);



	/* If it's a new queue, it will be marked as started at this point.

	 * Stop it before updating txq2sq.

	 */

	mlx5e_tx_disable_queue(netdev_get_tx_queue(priv->netdev, qid));



	priv->txq2sq[qid] = sq;



	/* Make the change to txq2sq visible before the queue is started.

	 * As mlx5e_xmit runs under a spinlock, there is an implicit ACQUIRE,
@@ -299,8 +310,13 @@ static void mlx5e_deactivate_qos_sq(struct mlx5e_priv *priv, u16 qid) 
	qos_dbg(priv->mdev, "Deactivate QoS SQ qid %u\n", qid);

	mlx5e_deactivate_txqsq(sq);



	/* The queue is disabled, no synchronization with datapath is needed. */

	priv->txq2sq[mlx5e_qid_from_qos(&priv->channels, qid)] = NULL;



	/* Make the change to txq2sq visible before the queue is started again.

	 * As mlx5e_xmit runs under a spinlock, there is an implicit ACQUIRE,

	 * which pairs with this barrier.

	 */

	smp_wmb();

}



static void mlx5e_close_qos_sq(struct mlx5e_priv *priv, u16 qid)

drivers/net/ethernet/mellanox/mlx5/core/en_tx.c

+13 −0
Original line number Diff line number Diff line
@@ -691,8 +691,21 @@ netdev_tx_t mlx5e_xmit(struct sk_buff *skb, struct net_device *dev) 
	struct mlx5e_txqsq *sq;

	u16 pi;



	/* All changes to txq2sq are performed in sync with mlx5e_xmit, when the

	 * queue being changed is disabled, and smp_wmb guarantees that the

	 * changes are visible before mlx5e_xmit tries to read from txq2sq. It

	 * guarantees that the value of txq2sq[qid] doesn't change while

	 * mlx5e_xmit is running on queue number qid. smb_wmb is paired with

	 * HARD_TX_LOCK around ndo_start_xmit, which serves as an ACQUIRE.

	 */

	sq = priv->txq2sq[skb_get_queue_mapping(skb)];

	if (unlikely(!sq)) {

		/* Two cases when sq can be NULL:

		 * 1. The HTB node is registered, and mlx5e_select_queue

		 * selected its queue ID, but the SQ itself is not yet created.

		 * 2. HTB SQ creation failed. Similar to the previous case, but

		 * the SQ won't be created.

		 */

		dev_kfree_skb_any(skb);

		return NETDEV_TX_OK;

	}