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mlx4: do not fire tasklet unless necessary

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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: Eric Dumazet <edumazet@google.com>
Cc: Tariq Toukan <tariqt@mellanox.com>
Cc: Saeed Mahameed <saeedm@mellanox.com>
Acked-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2017-02-10 04:27:58 -08:00 committed by David S. Miller
parent 99d5ceeea5
commit 01f0f42534
2 changed files with 6 additions and 9 deletions
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6
drivers/net/ethernet/mellanox/mlx4/cq.c
View File

@ -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);
}

9
drivers/net/ethernet/mellanox/mlx4/eq.c
View File

@ -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;
}