[PATCH] net/mlx5: fix spurious CPU wakeups caused by invalid CQE

[PATCH] net/mlx5: fix spurious CPU wakeups caused by invalid CQE

[Sivaprasad Tummala]

Previously, the PMD used a common monitor callback to determine
CQE ownership for power-aware polling. However, when a CQE contained
an invalid opcode(MLX5_CQE_INVALID), ownership bit was not reliable.
As a result, the monitor condition could falsely indicate CQE
availability and cause the CPU to wake up unnecessarily during
low traffic periods.

This resulted in spurious wakeups in monitor-wait mode and reduced
the expected power savings, as cores exited the sleep state even
when no valid CQEs were available.

This patch introduces a dedicated callback that skips invalid CQEs
and optimizes power efficiency by preventing false wakeups caused
by hardware-owned or invalid entries.

Fixes: a8f0df6bf98d ("net/mlx5: support power monitoring")
Cc: akozyrev@nvidia.com
Cc: stable@dpdk.org

Signed-off-by: Sivaprasad Tummala <sivaprasad.tummala@amd.com>
---
 drivers/net/mlx5/mlx5_rx.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/net/mlx5/mlx5_rx.c b/drivers/net/mlx5/mlx5_rx.c
index 420a03068d..2765b4b730 100644
--- a/drivers/net/mlx5/mlx5_rx.c
+++ b/drivers/net/mlx5/mlx5_rx.c
@@ -295,6 +295,20 @@ mlx5_monitor_callback(const uint64_t value,
 	return (value & m) == v ? -1 : 0;
 }
 
+static int
+mlx5_monitor_cqe_own_callback(const uint64_t value,
+		const uint64_t opaque[RTE_POWER_MONITOR_OPAQUE_SZ])
+{
+	const uint64_t m = opaque[CLB_MSK_IDX];
+	const uint64_t v = opaque[CLB_VAL_IDX];
+	const uint64_t match = ((value & m) == v);
+	const uint64_t opcode = MLX5_CQE_OPCODE(value);
+	const uint64_t valid_op = (opcode ^ MLX5_CQE_INVALID);
+
+	/* ownership bit is not valid for invalid opcode; CQE is HW owned */
+	return -(match & valid_op);
+}
+
 int mlx5_get_monitor_addr(void *rx_queue, struct rte_power_monitor_cond *pmc)
 {
 	struct mlx5_rxq_data *rxq = rx_queue;
@@ -312,12 +326,13 @@ int mlx5_get_monitor_addr(void *rx_queue, struct rte_power_monitor_cond *pmc)
 		pmc->addr = &cqe->validity_iteration_count;
 		pmc->opaque[CLB_VAL_IDX] = vic;
 		pmc->opaque[CLB_MSK_IDX] = MLX5_CQE_VIC_INIT;
+		pmc->fn = mlx5_monitor_callback;
 	} else {
 		pmc->addr = &cqe->op_own;
 		pmc->opaque[CLB_VAL_IDX] = !!idx;
 		pmc->opaque[CLB_MSK_IDX] = MLX5_CQE_OWNER_MASK;
+		pmc->fn = mlx5_monitor_cqe_own_callback;
 	}
-	pmc->fn = mlx5_monitor_callback;
 	pmc->size = sizeof(uint8_t);
 	return 0;
 }
-- 
2.43.0