[PATCH 4.2.y-ckt 94/98] net/mlx5e: Remove wrong poll CQ optimization

Kamal Mostafa
2016-03-15T23:31:28Z

From: Tariq Toukan <tariqt@mellanox.com>

commit 59a7c2fd336eaafb030aac9c91ac21d136a99f33 upstream.

With the MLX5E_CQ_HAS_CQES optimization flag, the following buggy
flow might occur:
- Suppose RX is always busy, TX has a single packet every second.
- We poll a single TX cqe and clear its flag.
- We never arm it again as RX is always busy.
- TX CQ flag is never changed, and new TX cqes are not polled.

We revert this optimization.

Fixes: e586b3b0baee ('net/mlx5: Ethernet Datapath files')
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[ kamal: backport to 4.2-stable: context around mlx5e_poll_rx_cq return ]
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
drivers/net/ethernet/mellanox/mlx5/core/en.h | 5 -----
drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 8 +-------
drivers/net/ethernet/mellanox/mlx5/core/en_tx.c | 10 +---------
drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c | 1 -
4 files changed, 2 insertions(+), 22 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en.h b/drivers/net/ethernet/mellanox/mlx5/core/en.h
index 3d23bd6..09e8331 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en.h
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en.h
@@ -201,14 +201,9 @@ enum {
MLX5E_RQ_STATE_POST_WQES_ENABLE,
};

-enum cq_flags {
- MLX5E_CQ_HAS_CQES = 1,
-};
-
struct mlx5e_cq {
/* data path - accessed per cqe */
struct mlx5_cqwq wq;
- unsigned long flags;

/* data path - accessed per napi poll */
struct napi_struct *napi;
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
index 9a93741..8a0e8a2 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
@@ -194,10 +194,6 @@ bool mlx5e_poll_rx_cq(struct mlx5e_cq *cq, int budget)
struct mlx5e_rq *rq = container_of(cq, struct mlx5e_rq, cq);
int i;

- /* avoid accessing cq (dma coherent memory) if not needed */
- if (!test_and_clear_bit(MLX5E_CQ_HAS_CQES, &cq->flags))
- return false;
-
for (i = 0; i < budget; i++) {
struct mlx5e_rx_wqe *wqe;
struct mlx5_cqe64 *cqe;
@@ -243,10 +239,8 @@ wq_ll_pop:
/* ensure cq space is freed before enabling more cqes */
wmb();

- if (i == budget) {
- set_bit(MLX5E_CQ_HAS_CQES, &cq->flags);
+ if (i == budget)
return true;
- }

return false;
}
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
index 03f28f4..3088081 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
@@ -262,10 +262,6 @@ bool mlx5e_poll_tx_cq(struct mlx5e_cq *cq)
u16 sqcc;
int i;

- /* avoid accessing cq (dma coherent memory) if not needed */
- if (!test_and_clear_bit(MLX5E_CQ_HAS_CQES, &cq->flags))
- return false;
-
sq = container_of(cq, struct mlx5e_sq, cq);

npkts = 0;
@@ -341,10 +337,6 @@ bool mlx5e_poll_tx_cq(struct mlx5e_cq *cq)
netif_tx_wake_queue(sq->txq);
sq->stats.wake++;
}
- if (i == MLX5E_TX_CQ_POLL_BUDGET) {
- set_bit(MLX5E_CQ_HAS_CQES, &cq->flags);
- return true;
- }

- return false;
+ return (i == MLX5E_TX_CQ_POLL_BUDGET);
}
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c
index 2c7cb67..ce29bca 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c
@@ -87,7 +87,6 @@ void mlx5e_completion_event(struct mlx5_core_cq *mcq)
{
struct mlx5e_cq *cq = container_of(mcq, struct mlx5e_cq, mcq);

- set_bit(MLX5E_CQ_HAS_CQES, &cq->flags);
set_bit(MLX5E_CHANNEL_NAPI_SCHED, &cq->channel->flags);
barrier();
napi_schedule(cq->napi);
--
2.7.0