[PATCH net-next V2 3/5] net/mlx5e: XDP, Remove stride size limitation

[Tariq Toukan]

From: Dragos Tatulea <dtatulea@xxxxxxxxxx>

Currently XDP mode always uses PAGE_SIZE strides. This limitation
existed because page fragment counting was not implemented when XDP was
added. Furthermore, due to this limitation there were other issues as
well on system with larger pages (e.g. 64K):

- XDP for Striding RQ was effectively disabled on such systems.

- Legacy RQ allows the configuration but uses a fixed scheme of one XDP
  buffer per page which is inefficient.

As fragment counting was added during the driver conversion to
page_pool and the support for XDP multi-buffer, it is now possible
to remove this stride size limitation. This patch does just that.

Now it is possible to use XDP on systems with higher page sizes (e.g.
64K):

- For Striding RQ, loading the program is no longer blocked.
  Although a 64K page can fit any packet, MTUs that result in
  stride > 8K will still make the RQ in non-linear mode. That's
  because the HW doesn't support a higher than 8K stride.

- For Legacy RQ, the stride size was PAGE_SIZE which was very
  inefficient. Now the stride size will be calculated relative to MTU.
  Legacy RQ will always be in linear mode for larger system pages.

  This can be observed with an XDP_DROP test [1] when running
  in Legacy RQ mode on a ARM Neoverse-N1 system with a 64K
  page size:
  +-----------------------------------------------+
  | MTU  | baseline   | this change | improvement |
  |------+------------+-------------+-------------|
  | 1500 | 15.55 Mpps | 18.99 Mpps  | 22.0 %      |
  | 9000 | 15.53 Mpps | 18.24 Mpps  | 17.5 %      |
  +-----------------------------------------------+

There are performance benefits for Striding RQ mode as well:

- Striding RQ non-linear mode now uses 256B strides, just like
  non-XDP mode.

- Striding RQ linear mode can now fit a number of XDP buffers per page
  that is relative to the MTU size. That means that on 4K page systems
  and a small enough MTU, 2 XDP buffers can fit in one page.

The above benefits for Striding RQ can be observed with an
XDP_DROP test [1] when running on a 4K page x86_64 system
(Intel Xeon Platinum 8580):
  +-----------------------------------------------+
  | MTU  | baseline   | this change | improvement |
  |------+------------+-------------+-------------|
  | 1000 | 28.36 Mpps | 33.98 Mpps  | 19.82 %     |
  | 9000 | 20.76 Mpps | 26.30 Mpps  | 26.70 %     |
  +-----------------------------------------------+

[1] Test description:
- xdp-bench with XDP_DROP
- RX: single queue
- TX: sends 64B packets to saturate CPU on RX side

Signed-off-by: Dragos Tatulea <dtatulea@xxxxxxxxxx>
Reviewed-by: Carolina Jubran <cjubran@xxxxxxxxxx>
Signed-off-by: Tariq Toukan <tariqt@xxxxxxxxxx>
---
 drivers/net/ethernet/mellanox/mlx5/core/en/params.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
index 26bb31c56e45..1f4a547917ba 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
@@ -298,12 +298,9 @@ static u32 mlx5e_rx_get_linear_stride_sz(struct mlx5_core_dev *mdev,
 	 * no_head_tail_room should be set in the case of XDP with Striding RQ
 	 * when SKB is not linear. This is because another page is allocated for the linear part.
 	 */
-	sz = roundup_pow_of_two(mlx5e_rx_get_linear_sz_skb(params, no_head_tail_room));
+	sz = mlx5e_rx_get_linear_sz_skb(params, no_head_tail_room);
 
-	/* XDP in mlx5e doesn't support multiple packets per page.
-	 * Do not assume sz <= PAGE_SIZE if params->xdp_prog is set.
-	 */
-	return params->xdp_prog && sz < PAGE_SIZE ? PAGE_SIZE : sz;
+	return roundup_pow_of_two(sz);
 }
 
 static u8 mlx5e_mpwqe_log_pkts_per_wqe(struct mlx5_core_dev *mdev,
@@ -453,10 +450,6 @@ u8 mlx5e_mpwqe_get_log_stride_size(struct mlx5_core_dev *mdev,
 		return order_base_2(mlx5e_rx_get_linear_stride_sz(mdev, params,
 								  rqo, true));
 
-	/* XDP in mlx5e doesn't support multiple packets per page. */
-	if (params->xdp_prog)
-		return PAGE_SHIFT;
-
 	return MLX5_MPWRQ_DEF_LOG_STRIDE_SZ(mdev);
 }
 
-- 
2.44.0