6.1-stable review patch. If anyone has any objections, please let me know.
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From: Armen Ratner armeng@nvidia.com
commit 8b0587a885fdb34fd6090a3f8625cb7ac1444826 upstream.
When port buffer headroom changes, port_update_shared_buffer() recalculates the shared buffer size and splits it in a 3:1 ratio (lossy:lossless) - Currently, the calculation is: lossless = shared / 4; lossy = (shared / 4) * 3;
Meaning, the calculation dropped the remainder of shared % 4 due to integer division, unintentionally reducing the total shared buffer by up to three cells on each update. Over time, this could shrink the buffer below usable size.
Fix it by changing the calculation to: lossless = shared / 4; lossy = shared - lossless;
This retains all buffer cells while still approximating the intended 3:1 split, preventing capacity loss over time.
While at it, perform headroom calculations in units of cells rather than in bytes for more accurate calculations avoiding extra divisions.
Fixes: a440030d8946 ("net/mlx5e: Update shared buffer along with device buffer changes") Signed-off-by: Armen Ratner armeng@nvidia.com Signed-off-by: Maher Sanalla msanalla@nvidia.com Reviewed-by: Tariq Toukan tariqt@nvidia.com Signed-off-by: Alexei Lazar alazar@nvidia.com Signed-off-by: Mark Bloch mbloch@nvidia.com Reviewed-by: Przemek Kitszel przemyslaw.kitszel@intel.com Link: https://patch.msgid.link/20250820133209.389065-9-mbloch@nvidia.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/ethernet/mellanox/mlx5/core/en/port_buffer.c | 18 ++++++--------- 1 file changed, 8 insertions(+), 10 deletions(-)
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/port_buffer.c +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/port_buffer.c @@ -272,8 +272,8 @@ static int port_update_shared_buffer(str /* Total shared buffer size is split in a ratio of 3:1 between * lossy and lossless pools respectively. */ - lossy_epool_size = (shared_buffer_size / 4) * 3; lossless_ipool_size = shared_buffer_size / 4; + lossy_epool_size = shared_buffer_size - lossless_ipool_size;
mlx5e_port_set_sbpr(mdev, 0, MLX5_EGRESS_DIR, MLX5_LOSSY_POOL, 0, lossy_epool_size); @@ -288,14 +288,12 @@ static int port_set_buffer(struct mlx5e_ u16 port_buff_cell_sz = priv->dcbx.port_buff_cell_sz; struct mlx5_core_dev *mdev = priv->mdev; int sz = MLX5_ST_SZ_BYTES(pbmc_reg); - u32 new_headroom_size = 0; - u32 current_headroom_size; + u32 current_headroom_cells = 0; + u32 new_headroom_cells = 0; void *in; int err; int i;
- current_headroom_size = port_buffer->headroom_size; - in = kzalloc(sz, GFP_KERNEL); if (!in) return -ENOMEM; @@ -306,12 +304,14 @@ static int port_set_buffer(struct mlx5e_
for (i = 0; i < MLX5E_MAX_NETWORK_BUFFER; i++) { void *buffer = MLX5_ADDR_OF(pbmc_reg, in, buffer[i]); + current_headroom_cells += MLX5_GET(bufferx_reg, buffer, size); + u64 size = port_buffer->buffer[i].size; u64 xoff = port_buffer->buffer[i].xoff; u64 xon = port_buffer->buffer[i].xon;
- new_headroom_size += size; do_div(size, port_buff_cell_sz); + new_headroom_cells += size; do_div(xoff, port_buff_cell_sz); do_div(xon, port_buff_cell_sz); MLX5_SET(bufferx_reg, buffer, size, size); @@ -320,10 +320,8 @@ static int port_set_buffer(struct mlx5e_ MLX5_SET(bufferx_reg, buffer, xon_threshold, xon); }
- new_headroom_size /= port_buff_cell_sz; - current_headroom_size /= port_buff_cell_sz; - err = port_update_shared_buffer(priv->mdev, current_headroom_size, - new_headroom_size); + err = port_update_shared_buffer(priv->mdev, current_headroom_cells, + new_headroom_cells); if (err) goto out;