net/mlx5e: Use kernel's mechanism to avoid missing NAPIs

We used a channel state bit MLX5E_CHANNEL_NAPI_SCHED to make
sure no NAPI is missed when a channel's napi_schedule() is called
for completion events of the different channel's resources/rings
while NAPI is currently running.
Now, as similar mechanism is implemented in kernel,
("39e6c8208d7b net: solve a NAPI race"),
we obsolete our own implementation and rely on the return value
of napi_complete_done().

This patch removes a redundant overhead of atomic bit operations.

Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/net/ethernet/mellanox/mlx5/core/en.h

@@ -570,10 +570,6 @@ struct mlx5e_rq {
 	struct mlx5_core_mkey  umr_mkey;
 } ____cacheline_aligned_in_smp;
 
-enum channel_flags {
-	MLX5E_CHANNEL_NAPI_SCHED = 1,
-};
-
 struct mlx5e_channel {
 	/* data path */
 	struct mlx5e_rq            rq;
@@ -585,7 +581,6 @@ struct mlx5e_channel {
 	struct net_device         *netdev;
 	__be32                     mkey_be;
 	u8                         num_tc;
-	unsigned long              flags;
 
 	/* control */
 	struct mlx5e_priv         *priv;

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

@@ -3697,7 +3697,6 @@ static int mlx5e_xdp_set(struct net_device *netdev, struct bpf_prog *prog)
 
 		set_bit(MLX5E_RQ_STATE_ENABLED, &c->rq.state);
 		/* napi_schedule in case we have missed anything */
-		set_bit(MLX5E_CHANNEL_NAPI_SCHED, &c->flags);
 		napi_schedule(&c->napi);
 
 		if (old_prog)

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

@@ -40,8 +40,6 @@ int mlx5e_napi_poll(struct napi_struct *napi, int budget)
 	int work_done;
 	int i;
 
-	clear_bit(MLX5E_CHANNEL_NAPI_SCHED, &c->flags);
-
 	for (i = 0; i < c->num_tc; i++)
 		busy |= mlx5e_poll_tx_cq(&c->sq[i].cq, budget);
 
@@ -56,13 +54,8 @@ int mlx5e_napi_poll(struct napi_struct *napi, int budget)
 	if (busy)
 		return budget;
 
-	napi_complete_done(napi, work_done);
-
-	/* avoid losing completion event during/after polling cqs */
-	if (test_bit(MLX5E_CHANNEL_NAPI_SCHED, &c->flags)) {
-		napi_schedule(napi);
+	if (unlikely(!napi_complete_done(napi, work_done)))
 		return work_done;
-	}
 
 	for (i = 0; i < c->num_tc; i++)
 		mlx5e_cq_arm(&c->sq[i].cq);
@@ -81,7 +74,6 @@ void mlx5e_completion_event(struct mlx5_core_cq *mcq)
 	struct mlx5e_cq *cq = container_of(mcq, struct mlx5e_cq, mcq);
 
 	cq->event_ctr++;
-	set_bit(MLX5E_CHANNEL_NAPI_SCHED, &cq->channel->flags);
 	napi_schedule(cq->napi);
 }