[PATCH net-next] mlx4: do not fire tasklet unless necessary
From: Eric Dumazet <hidden>
Date: 2017-02-10 12:56:14
Subsystem:
mellanox mlx4 core vpi driver, networking drivers, the rest · Maintainers:
Tariq Toukan, Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
From: Eric Dumazet <edumazet@google.com> 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 <redacted> Cc: Saeed Mahameed <redacted> --- drivers/net/ethernet/mellanox/mlx4/cq.c | 6 +++++- drivers/net/ethernet/mellanox/mlx4/eq.c | 9 +-------- 2 files changed, 6 insertions(+), 9 deletions(-)
diff --git a/drivers/net/ethernet/mellanox/mlx4/cq.c b/drivers/net/ethernet/mellanox/mlx4/cq.c
index 6b8635378f1fcb2aae4e8ac390bcd09d552c2256..fa6d2354a0e910ee160863e3cbe21a512d77bf03 100644
--- a/drivers/net/ethernet/mellanox/mlx4/cq.c
+++ b/drivers/net/ethernet/mellanox/mlx4/cq.c@@ -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); }
diff --git a/drivers/net/ethernet/mellanox/mlx4/eq.c b/drivers/net/ethernet/mellanox/mlx4/eq.c
index 0509996957d9664b612358dd805359f4bc67b8dc..39232b6a974f4b4b961d3b0b8634f04e6b9d0caa 100644
--- a/drivers/net/ethernet/mellanox/mlx4/eq.c
+++ b/drivers/net/ethernet/mellanox/mlx4/eq.c@@ -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; }