netdev - [net-next 05/16] net/mlx5: Pack mlx5_rl

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Date:   Sat,  3 Apr 2021 21:19:43 -0700
From:   Saeed Mahameed <saeed@...nel.org>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, Tariq Toukan <tariqt@...dia.com>,
        Parav Pandit <parav@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: [net-next 05/16] net/mlx5: Pack mlx5_rl_entry structure

From: Parav Pandit <parav@...dia.com>

mlx5_rl_entry structure is not properly packed as shown below. Due to this
an array of size 9144 bytes allocated which is aligned to 16Kbytes.
Hence, pack the structure and avoid the wastage.

This offers 8Kbytes of saving per mlx5_core_dev struct.

pahole -C mlx5_rl_entry  drivers/net/ethernet/mellanox/mlx5/core/en_main.o

Existing layout:

struct mlx5_rl_entry {
        u8                         rl_raw[48];           /*     0    48 */
        u16                        index;                /*    48     2 */

        /* XXX 6 bytes hole, try to pack */

        u64                        refcount;             /*    56     8 */
        /* --- cacheline 1 boundary (64 bytes) --- */
        u16                        uid;                  /*    64     2 */
        u8                         dedicated:1;          /*    66: 0  1 */

        /* size: 72, cachelines: 2, members: 5 */
        /* sum members: 60, holes: 1, sum holes: 6 */
        /* sum bitfield members: 1 bits (0 bytes) */
        /* padding: 5 */
        /* bit_padding: 7 bits */
        /* last cacheline: 8 bytes */
};

After alignment:

struct mlx5_rl_entry {
        u8                         rl_raw[48];           /*     0    48 */
        u64                        refcount;             /*    48     8 */
        u16                        index;                /*    56     2 */
        u16                        uid;                  /*    58     2 */
        u8                         dedicated:1;          /*    60: 0  1 */

        /* size: 64, cachelines: 1, members: 5 */
        /* padding: 3 */
        /* bit_padding: 7 bits */
};

Signed-off-by: Parav Pandit <parav@...dia.com>
Signed-off-by: Saeed Mahameed <saeedm@...dia.com>
---
 include/linux/mlx5/driver.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/mlx5/driver.h b/include/linux/mlx5/driver.h
index 23bb01d7c9b9..a9bd7e3bd554 100644
--- a/include/linux/mlx5/driver.h
+++ b/include/linux/mlx5/driver.h
@@ -517,8 +517,8 @@ struct mlx5_rate_limit {
 
 struct mlx5_rl_entry {
 	u8 rl_raw[MLX5_ST_SZ_BYTES(set_pp_rate_limit_context)];
-	u16 index;
 	u64 refcount;
+	u16 index;
 	u16 uid;
 	u8 dedicated : 1;
 };
-- 
2.30.2