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

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Message-ID: <Z4fpMRF1hfytUnla@lzaremba-mobl.ger.corp.intel.com>
Date: Wed, 15 Jan 2025 17:58:25 +0100
From: Larysa Zaremba <larysa.zaremba@...el.com>
To: Furong Xu <0x1207@...il.com>
CC: <netdev@...r.kernel.org>, <linux-stm32@...md-mailman.stormreply.com>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	Alexander Lobakin <aleksander.lobakin@...el.com>, Joe Damato
	<jdamato@...tly.com>, Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Maxime Coquelin
	<mcoquelin.stm32@...il.com>, <xfr@...look.com>
Subject: Re: [PATCH net-next v3 1/4] net: stmmac: Switch to zero-copy in
 non-XDP RX path

On Wed, Jan 15, 2025 at 11:27:02AM +0800, Furong Xu wrote:
> 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@...il.com>
> Reviewed-by: Alexander Lobakin <aleksander.lobakin@...el.com>

Reviewed-by: Larysa Zaremba <larysa.zaremba@...el.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
> 
>