net/mlx5e: Make the wqe_index_mask calculation more exact

The old calculation of wqe_index_mask may give false positives, i.e.
request bulking of pairs of WQEs when not strictly needed, for example,
when the first fragment size is equal to the PAGE_SIZE, bulking is not
needed, even if the number of fragments is odd.

Make the calculation more exact to cut false positives.

Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
index 49306a68b3b5603d1576a41a6b1203480c5dd8bc..ac4d70bb21e815322b3c0b2cd52539e75bad3fa2 100644 (file)
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
@@ -648,7 +648,26 @@ static int mlx5e_build_rq_frags_info(struct mlx5_core_dev *mdev,
         * is not completed yet, WQE 2*N must not be allocated, as it's
         * responsible for allocating a new page.
         */
-       info->wqe_index_mask = info->num_frags % 2;
+       if (frag_size_max == PAGE_SIZE) {
+               /* No WQE can start in the middle of a page. */
+               info->wqe_index_mask = 0;
+       } else {
+               /* PAGE_SIZEs starting from 8192 don't use 2K-sized fragments,
+                * because there would be more than MLX5E_MAX_RX_FRAGS of them.
+                */
+               WARN_ON(PAGE_SIZE != 2 * DEFAULT_FRAG_SIZE);
+
+               /* Odd number of fragments allows to pack the last fragment of
+                * the previous WQE and the first fragment of the next WQE into
+                * the same page.
+                * As long as DEFAULT_FRAG_SIZE is 2048, and MLX5E_MAX_RX_FRAGS
+                * is 4, the last fragment can be bigger than the rest only if
+                * it's the fourth one, so WQEs consisting of 3 fragments will
+                * always share a page.
+                * When a page is shared, WQE bulk size is 2, otherwise just 1.
+                */
+               info->wqe_index_mask = info->num_frags % 2;
+       }
 
 out:
        /* Bulking optimization to skip allocation until at least 8 WQEs can be