[dpdk-dev] [PATCH] common/mlx5: fix receiving queue doorbell register size

[Viacheslav Ovsiienko]

When received queue is being created with DevX the allocated
doorbell register size is only uint64_t. That is definitely
less than size of CPU cacheline and it might happen the
registers attached to different queues handled by different
cores are allocated within same cacheline. It might cause
contention on doorbell register writing.

This patch extends the allocated memory size for doorbell
register to cacheline size.

Fixes: 21cae8580fd0 ("net/mlx5: allocate door-bells via DevX")
Cc: stable at dpdk.org

Signed-off-by: Viacheslav Ovsiienko <viacheslavo at mellanox.com>
---
 drivers/common/mlx5/mlx5_common.c |  2 +-
 drivers/common/mlx5/mlx5_common.h | 10 ++++++----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/common/mlx5/mlx5_common.c b/drivers/common/mlx5/mlx5_common.c
index 79cd5ba..193e73b 100644
--- a/drivers/common/mlx5/mlx5_common.c
+++ b/drivers/common/mlx5/mlx5_common.c
@@ -187,7 +187,7 @@ static inline void mlx5_cpu_id(unsigned int level,
 	page->dbr_bitmap[i] |= (UINT64_C(1) << j);
 	page->dbr_count++;
 	*dbr_page = page;
-	return (((i * 64) + j) * sizeof(uint64_t));
+	return (i * CHAR_BIT * sizeof(uint64_t) + j) * MLX5_DBR_SIZE;
 }
 
 /**
diff --git a/drivers/common/mlx5/mlx5_common.h b/drivers/common/mlx5/mlx5_common.h
index 5b9b7bd..ef7b61b 100644
--- a/drivers/common/mlx5/mlx5_common.h
+++ b/drivers/common/mlx5/mlx5_common.h
@@ -214,10 +214,12 @@ enum mlx5_class {
 	MLX5_CLASS_VDPA = RTE_BIT64(1),
 };
 
-#define MLX5_DBR_PAGE_SIZE 4096 /* Must be >= 512. */
-#define MLX5_DBR_SIZE 8
-#define MLX5_DBR_PER_PAGE (MLX5_DBR_PAGE_SIZE / MLX5_DBR_SIZE)
-#define MLX5_DBR_BITMAP_SIZE (MLX5_DBR_PER_PAGE / 64)
+#define MLX5_DBR_SIZE RTE_CACHE_LINE_SIZE
+#define MLX5_DBR_PER_PAGE 64
+/* Must be >= CHAR_BIT * sizeof(uint64_t) */
+#define MLX5_DBR_PAGE_SIZE (MLX5_DBR_PER_PAGE * MLX5_DBR_SIZE)
+/* Page size must be >= 512. */
+#define MLX5_DBR_BITMAP_SIZE (MLX5_DBR_PER_PAGE / (CHAR_BIT * sizeof(uint64_t)))
 
 struct mlx5_devx_dbr_page {
 	/* Door-bell records, must be first member in structure. */
-- 
1.8.3.1