[PATCH net-next v3 1/4] net: stmmac: Switch to zero-copy in non-XDP RX path

Furong Xu
2025-01-15T03:27:32Z

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>
---
drivers/net/ethernet/stmicro/stmmac/stmmac.h | 1 +
.../net/ethernet/stmicro/stmmac/stmmac_main.c | 26 ++++++++++++-------
2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
index e8dbce20129c..f05cae103d83 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
+++ b/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;
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index acd6994c1764..1d98a5e8c98c 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/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,
--
2.34.1