Commit 01f0f425 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

mlx4: do not fire tasklet unless necessary 



All rx and rx netdev interrupts are handled by respectively
by mlx4_en_rx_irq() and mlx4_en_tx_irq() which simply schedule a NAPI.

But mlx4_eq_int() also fires a tasklet to service all items that were
queued via mlx4_add_cq_to_tasklet(), but this handler was not called
unless user cqe was handled.

This is very confusing, as "mpstat -I SCPU ..." show huge number of
tasklet invocations.

This patch saves this overhead, by carefully firing the tasklet directly
from mlx4_add_cq_to_tasklet(), removing four atomic operations per IRQ.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Tariq Toukan <tariqt@mellanox.com>
Cc: Saeed Mahameed <saeedm@mellanox.com>
Acked-by: default avatarSaeed Mahameed <saeedm@mellanox.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 99d5ceee

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

+5 −1
Original line number Diff line number Diff line
@@ -81,8 +81,9 @@ void mlx4_cq_tasklet_cb(unsigned long data) 


static void mlx4_add_cq_to_tasklet(struct mlx4_cq *cq)

{

	unsigned long flags;

	struct mlx4_eq_tasklet *tasklet_ctx = cq->tasklet_ctx.priv;

	unsigned long flags;

	bool kick;



	spin_lock_irqsave(&tasklet_ctx->lock, flags);

	/* When migrating CQs between EQs will be implemented, please note
@@ -92,7 +93,10 @@ static void mlx4_add_cq_to_tasklet(struct mlx4_cq *cq) 
	 */

	if (list_empty_careful(&cq->tasklet_ctx.list)) {

		atomic_inc(&cq->refcount);

		kick = list_empty(&tasklet_ctx->list);

		list_add_tail(&cq->tasklet_ctx.list, &tasklet_ctx->list);

		if (kick)

			tasklet_schedule(&tasklet_ctx->task);

	}

	spin_unlock_irqrestore(&tasklet_ctx->lock, flags);

}

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

+1 −8
Original line number Diff line number Diff line
@@ -494,7 +494,7 @@ static int mlx4_eq_int(struct mlx4_dev *dev, struct mlx4_eq *eq) 
{

	struct mlx4_priv *priv = mlx4_priv(dev);

	struct mlx4_eqe *eqe;

	int cqn = -1;

	int cqn;

	int eqes_found = 0;

	int set_ci = 0;

	int port;
@@ -840,13 +840,6 @@ static int mlx4_eq_int(struct mlx4_dev *dev, struct mlx4_eq *eq) 


	eq_set_ci(eq, 1);



	/* cqn is 24bit wide but is initialized such that its higher bits

	 * are ones too. Thus, if we got any event, cqn's high bits should be off

	 * and we need to schedule the tasklet.

	 */

	if (!(cqn & ~0xffffff))

		tasklet_schedule(&eq->tasklet_ctx.task);



	return eqes_found;

}

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