net: stmmac: Switch to zero-copy in non-XDP RX path

Avoid memcpy in non-XDP RX path by marking all allocated SKBs to
be recycled in the upper network stack.

This patch brings ~11.5% driver performance improvement in a TCP RX
throughput test with iPerf tool on a single isolated Cortex-A65 CPU
core, from 2.18 Gbits/sec increased to 2.43 Gbits/sec.

Signed-off-by: Furong Xu <0x1207@gmail.com>
Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Larysa Zaremba <larysa.zaremba@intel.com>
Reviewed-by: Yanteng Si <si.yanteng@linux.dev>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ethernet/stmicro/stmmac/stmmac.h

@@ -126,6 +126,7 @@ struct stmmac_rx_queue {
 	unsigned int cur_rx;
 	unsigned int dirty_rx;
 	unsigned int buf_alloc_num;
+	unsigned int napi_skb_frag_size;
 	dma_addr_t dma_rx_phy;
 	u32 rx_tail_addr;
 	unsigned int state_saved;

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -1341,7 +1341,7 @@ static unsigned int stmmac_rx_offset(struct stmmac_priv *priv)
 	if (stmmac_xdp_is_enabled(priv))
 		return XDP_PACKET_HEADROOM;
 
-	return 0;
+	return NET_SKB_PAD;
 }
 
 static int stmmac_set_bfsize(int mtu, int bufsize)
@@ -2040,17 +2040,21 @@ static int __alloc_dma_rx_desc_resources(struct stmmac_priv *priv,
 	struct stmmac_channel *ch = &priv->channel[queue];
 	bool xdp_prog = stmmac_xdp_is_enabled(priv);
 	struct page_pool_params pp_params = { 0 };
-	unsigned int num_pages;
+	unsigned int dma_buf_sz_pad, num_pages;
 	unsigned int napi_id;
 	int ret;
 
+	dma_buf_sz_pad = stmmac_rx_offset(priv) + dma_conf->dma_buf_sz +
+			 SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+	num_pages = DIV_ROUND_UP(dma_buf_sz_pad, PAGE_SIZE);
+
 	rx_q->queue_index = queue;
 	rx_q->priv_data = priv;
+	rx_q->napi_skb_frag_size = num_pages * PAGE_SIZE;
 
 	pp_params.flags = PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV;
 	pp_params.pool_size = dma_conf->dma_rx_size;
-	num_pages = DIV_ROUND_UP(dma_conf->dma_buf_sz, PAGE_SIZE);
-	pp_params.order = ilog2(num_pages);
+	pp_params.order = order_base_2(num_pages);
 	pp_params.nid = dev_to_node(priv->device);
 	pp_params.dev = priv->device;
 	pp_params.dma_dir = xdp_prog ? DMA_BIDIRECTIONAL : DMA_FROM_DEVICE;
@@ -5582,22 +5586,26 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 		}
 
 		if (!skb) {
+			unsigned int head_pad_len;
+
 			/* XDP program may expand or reduce tail */
 			buf1_len = ctx.xdp.data_end - ctx.xdp.data;
 
-			skb = napi_alloc_skb(&ch->rx_napi, buf1_len);
+			skb = napi_build_skb(page_address(buf->page),
+					     rx_q->napi_skb_frag_size);
 			if (!skb) {
+				page_pool_recycle_direct(rx_q->page_pool,
+							 buf->page);
 				rx_dropped++;
 				count++;
 				goto drain_data;
 			}
 
 			/* XDP program may adjust header */
-			skb_copy_to_linear_data(skb, ctx.xdp.data, buf1_len);
+			head_pad_len = ctx.xdp.data - ctx.xdp.data_hard_start;
+			skb_reserve(skb, head_pad_len);
 			skb_put(skb, buf1_len);
-
-			/* Data payload copied into SKB, page ready for recycle */
-			page_pool_recycle_direct(rx_q->page_pool, buf->page);
+			skb_mark_for_recycle(skb);
 			buf->page = NULL;
 		} else if (buf1_len) {
 			dma_sync_single_for_cpu(priv->device, buf->addr,