Author: hselasky
Date: Thu Sep 6 11:06:07 2018
New Revision: 338489
URL: https://svnweb.freebsd.org/changeset/base/338489
Log:
Maximum number of mbuf frags is off-by-one for worst case scenario in
mlx5en(4).
Inspecting the PRM no more than 0x3F data segments, DS, of size 16 bytes is
allowed.
Worst case scenario summary of DS usage:
Header is fixed: 2 DS
Maximum inlining: 98 => (98 - 2) / 16 = 6 DS
Remainder: 0x3F - 2 - 6 = 55 DS (mbuf frags)
Previously a value of 56 DS was used and this would work in the
normal case because not all inline data area was used up.
MFC after: 3 days
Approved by: re (marius)
Sponsored by: Mellanox Technologies
Modified:
head/sys/dev/mlx5/mlx5_en/en.h
Modified: head/sys/dev/mlx5/mlx5_en/en.h
==============================================================================
--- head/sys/dev/mlx5/mlx5_en/en.h Thu Sep 6 07:10:49 2018
(r338488)
+++ head/sys/dev/mlx5/mlx5_en/en.h Thu Sep 6 11:06:07 2018
(r338489)
@@ -123,7 +123,8 @@
#define MLX5E_MAX_TX_MBUF_SIZE 65536 /* bytes */
#define MLX5E_MAX_TX_MBUF_FRAGS \
((MLX5_SEND_WQE_MAX_WQEBBS * MLX5_SEND_WQEBB_NUM_DS) - \
- (MLX5E_MAX_TX_HEADER / MLX5_SEND_WQE_DS)) /* units */
+ (MLX5E_MAX_TX_HEADER / MLX5_SEND_WQE_DS) - \
+ 1 /* the maximum value of the DS counter is 0x3F and not 0x40 */) /*
units */
#define MLX5E_MAX_TX_INLINE \
(MLX5E_MAX_TX_HEADER - sizeof(struct mlx5e_tx_wqe) + \
sizeof(((struct mlx5e_tx_wqe *)0)->eth.inline_hdr_start)) /* bytes */
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