net/mlx5e: RX, Defer page release in legacy rq for better recycling

Currently, fragmented pages from the page pool can be released
in two ways:

1) In the mlx5e driver when trimming off the unused fragments AND the
associated skb fragments have been released. This path allows
recycling of pages to the page pool cache (allow_direct == true).

2) On the skb release path (last fragment release), which
will always release pages to the page pool ring
(allow_direct == false).

Whichever is releasing the last fragment will be decisive on
where the page gets released: the cache or the ring. So we
obviously want to maximize for doing the release from 1.

This patch does that by deferring the release of page fragments
right before requesting new ones from the page pool. A flag is
added to make sure that there's no release before first alloc
and that XDP_TX fragments are not released prematurely.

This is a preparation patch that doesn't unlock the performance
improvements yet. A followup patch will do that.

Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

1 files changed, 19 insertions, 1 deletions

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
index bb1cbf008876..3cf7d2b59037 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
@@ -520,6 +520,9 @@ static void mlx5e_init_frags_partition(struct mlx5e_rq *rq)
 
 	next_frag.frag_page = &rq->wqe.alloc_units->frag_pages[0];
 
+	/* Skip first release due to deferred release. */
+	next_frag.flags = BIT(MLX5E_WQE_FRAG_SKIP_RELEASE);
+
 	for (i = 0; i < mlx5_wq_cyc_get_size(&rq->wqe.wq); i++) {
 		struct mlx5e_rq_frag_info *frag_info = &rq->wqe.info.arr[0];
 		struct mlx5e_wqe_frag_info *frag =
@@ -558,8 +561,14 @@ static void mlx5e_init_xsk_buffs(struct mlx5e_rq *rq)
 	/* Considering the above assumptions a fragment maps to a single
 	 * xsk_buff.
 	 */
-	for (i = 0; i < mlx5_wq_cyc_get_size(&rq->wqe.wq); i++)
+	for (i = 0; i < mlx5_wq_cyc_get_size(&rq->wqe.wq); i++) {
 		rq->wqe.frags[i].xskp = &rq->wqe.alloc_units->xsk_buffs[i];
+
+		/* Skip first release due to deferred release as WQES are
+		 * not allocated yet.
+		 */
+		rq->wqe.frags[i].flags |= BIT(MLX5E_WQE_FRAG_SKIP_RELEASE);
+	}
 }
 
 static int mlx5e_init_wqe_alloc_info(struct mlx5e_rq *rq, int node)
@@ -1183,12 +1192,21 @@ void mlx5e_free_rx_descs(struct mlx5e_rq *rq)
 						0, true);
 	} else {
 		struct mlx5_wq_cyc *wq = &rq->wqe.wq;
+		u16 missing = mlx5_wq_cyc_missing(wq);
+		u16 head = mlx5_wq_cyc_get_head(wq);
 
 		while (!mlx5_wq_cyc_is_empty(wq)) {
 			wqe_ix = mlx5_wq_cyc_get_tail(wq);
 			rq->dealloc_wqe(rq, wqe_ix);
 			mlx5_wq_cyc_pop(wq);
 		}
+		/* Missing slots might also contain unreleased pages due to
+		 * deferred release.
+		 */
+		while (missing--) {
+			wqe_ix = mlx5_wq_cyc_ctr2ix(wq, head++);
+			rq->dealloc_wqe(rq, wqe_ix);
+		}
 	}
 
 }