From d451994ebc7d4392610bd4b2ab339b255deb4143 Mon Sep 17 00:00:00 2001 From: Gal Pressman Date: Wed, 18 Feb 2026 09:29:01 +0200 Subject: [PATCH] net/mlx5: Fix misidentification of write combining CQE during poll loop The write combining completion poll loop uses usleep_range() which can sleep much longer than requested due to scheduler latency. Under load, we witnessed a 20ms+ delay until the process was rescheduled, causing the jiffies based timeout to expire while the thread is sleeping. The original do-while loop structure (poll, sleep, check timeout) would exit without a final poll when waking after timeout, missing a CQE that arrived during sleep. Instead of the open-coded while loop, use the kernel's poll_timeout_us() which always performs an additional check after the sleep expiration, and is less error-prone. Note: poll_timeout_us() doesn't accept a sleep range, by passing 10 sleep_us the sleep range effectively changes from 2-10 to 3-10 usecs. Fixes: d98995b4bf98 ("net/mlx5: Reimplement write combining test") Signed-off-by: Gal Pressman Reviewed-by: Jianbo Liu Signed-off-by: Tariq Toukan Reviewed-by: Jacob Keller Link: https://patch.msgid.link/20260218072904.1764634-4-tariqt@nvidia.com Signed-off-by: Jakub Kicinski --- drivers/net/ethernet/mellanox/mlx5/core/wc.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-) diff --git a/drivers/net/ethernet/mellanox/mlx5/core/wc.c b/drivers/net/ethernet/mellanox/mlx5/core/wc.c index 815a7c97d6b0..04d03be1bb77 100644 --- a/drivers/net/ethernet/mellanox/mlx5/core/wc.c +++ b/drivers/net/ethernet/mellanox/mlx5/core/wc.c @@ -2,6 +2,7 @@ // Copyright (c) 2024, NVIDIA CORPORATION & AFFILIATES. All rights reserved. #include +#include #include #include "lib/clock.h" #include "mlx5_core.h" @@ -15,7 +16,7 @@ #define TEST_WC_NUM_WQES 255 #define TEST_WC_LOG_CQ_SZ (order_base_2(TEST_WC_NUM_WQES)) #define TEST_WC_SQ_LOG_WQ_SZ TEST_WC_LOG_CQ_SZ -#define TEST_WC_POLLING_MAX_TIME_JIFFIES msecs_to_jiffies(100) +#define TEST_WC_POLLING_MAX_TIME_USEC (100 * USEC_PER_MSEC) struct mlx5_wc_cq { /* data path - accessed per cqe */ @@ -359,7 +360,6 @@ static int mlx5_wc_poll_cq(struct mlx5_wc_sq *sq) static void mlx5_core_test_wc(struct mlx5_core_dev *mdev) { unsigned int offset = 0; - unsigned long expires; struct mlx5_wc_sq *sq; int i, err; @@ -389,13 +389,9 @@ static void mlx5_core_test_wc(struct mlx5_core_dev *mdev) mlx5_wc_post_nop(sq, &offset, true); - expires = jiffies + TEST_WC_POLLING_MAX_TIME_JIFFIES; - do { - err = mlx5_wc_poll_cq(sq); - if (err) - usleep_range(2, 10); - } while (mdev->wc_state == MLX5_WC_STATE_UNINITIALIZED && - time_is_after_jiffies(expires)); + poll_timeout_us(mlx5_wc_poll_cq(sq), + mdev->wc_state != MLX5_WC_STATE_UNINITIALIZED, 10, + TEST_WC_POLLING_MAX_TIME_USEC, false); mlx5_wc_destroy_sq(sq); -- 2.30.2