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

Yanteng Si
2025-01-16T02:05:48Z

在 2025/1/15 11:27, Furong Xu 写道:
> 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: Yanteng Si <si.yanteng@linux.dev>

Thanks,
Yanteng
> ---
> 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,