linux-kernel - Re: [PATCH net-next v6 08/12] libie: add Rx buffer management (via Page Pool)

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Message-ID: <1103fe8f-04c8-8cc4-8f1b-ff45cea22b54@huawei.com>
Date:   Fri, 8 Dec 2023 17:28:21 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
CC:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Michal Kubiak <michal.kubiak@...el.com>,
        Larysa Zaremba <larysa.zaremba@...el.com>,
        Alexander Duyck <alexanderduyck@...com>,
        David Christensen <drc@...ux.vnet.ibm.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Paul Menzel <pmenzel@...gen.mpg.de>, <netdev@...r.kernel.org>,
        <intel-wired-lan@...ts.osuosl.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v6 08/12] libie: add Rx buffer management (via
 Page Pool)

On 2023/12/8 1:20, Alexander Lobakin wrote:
...

> +
> +/**
> + * libie_rx_page_pool_create - create a PP with the default libie settings
> + * @bq: buffer queue struct to fill
> + * @napi: &napi_struct covering this PP (no usage outside its poll loops)
> + *
> + * Return: 0 on success, -errno on failure.
> + */
> +int libie_rx_page_pool_create(struct libie_buf_queue *bq,
> +			      struct napi_struct *napi)
> +{
> +	struct page_pool_params pp = {
> +		.flags		= PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV,
> +		.order		= LIBIE_RX_PAGE_ORDER,
> +		.pool_size	= bq->count,
> +		.nid		= NUMA_NO_NODE,

Is there a reason the NUMA_NO_NODE is used here instead of
dev_to_node(napi->dev->dev.parent)?

> +		.dev		= napi->dev->dev.parent,
> +		.netdev		= napi->dev,
> +		.napi		= napi,
> +		.dma_dir	= DMA_FROM_DEVICE,
> +		.offset		= LIBIE_SKB_HEADROOM,
> +	};
> +
> +	/* HW-writeable / syncable length per one page */
> +	pp.max_len = LIBIE_RX_BUF_LEN(pp.offset);
> +
> +	/* HW-writeable length per buffer */
> +	bq->rx_buf_len = libie_rx_hw_len(&pp);
> +	/* Buffer size to allocate */
> +	bq->truesize = roundup_pow_of_two(SKB_HEAD_ALIGN(pp.offset +
> +							 bq->rx_buf_len));
> +
> +	bq->pp = page_pool_create(&pp);
> +
> +	return PTR_ERR_OR_ZERO(bq->pp);
> +}
> +EXPORT_SYMBOL_NS_GPL(libie_rx_page_pool_create, LIBIE);
> +

...

> +/**
> + * libie_rx_sync_for_cpu - synchronize or recycle buffer post DMA
> + * @buf: buffer to process
> + * @len: frame length from the descriptor
> + *
> + * Process the buffer after it's written by HW. The regular path is to
> + * synchronize DMA for CPU, but in case of no data it will be immediately
> + * recycled back to its PP.
> + *
> + * Return: true when there's data to process, false otherwise.
> + */
> +static inline bool libie_rx_sync_for_cpu(const struct libie_rx_buffer *buf,
> +					 u32 len)
> +{
> +	struct page *page = buf->page;
> +
> +	/* Very rare, but possible case. The most common reason:
> +	 * the last fragment contained FCS only, which was then
> +	 * stripped by the HW.
> +	 */
> +	if (unlikely(!len)) {
> +		page_pool_recycle_direct(page->pp, page);
> +		return false;
> +	}
> +
> +	page_pool_dma_sync_for_cpu(page->pp, page, buf->offset, len);

Is there a reason why page_pool_dma_sync_for_cpu() is still used when
page_pool_create() is called with PP_FLAG_DMA_SYNC_DEV flag? Isn't syncing
already handled in page_pool core when when PP_FLAG_DMA_SYNC_DEV flag is
set?

> +
> +	return true;
> +}
>  
>  /* O(1) converting i40e/ice/iavf's 8/10-bit hardware packet type to a parsed
>   * bitfield struct.
>