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net/mlx5: Fix misidentification of write combining CQE during poll loop

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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: d98995b4bf ("net/mlx5: Reimplement write combining test")
Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Jianbo Liu <jianbol@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Jacob Keller <Jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20260218072904.1764634-4-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Gal Pressman
2026-02-18 09:29:01 +02:00
committed by Jakub Kicinski
parent ae3cb71e6c
commit d451994ebc
1 changed files with 5 additions and 9 deletions
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14
drivers/net/ethernet/mellanox/mlx5/core/wc.c
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@@ -2,6 +2,7 @@
// Copyright (c) 2024, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
#include <linux/io.h>
#include <linux/iopoll.h>
#include <linux/mlx5/transobj.h>
#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);