Re: [PATCH 2/7] net: mvneta: introduce page pool API for sw buffer manager

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

Hi Lorenzo, 

On Sat, Oct 05, 2019 at 10:44:35PM +0200, Lorenzo Bianconi wrote:
> Use the page_pool api for allocations and DMA handling instead of
> __dev_alloc_page()/dma_map_page() and free_page()/dma_unmap_page().
> Pages are unmapped using page_pool_release_page before packets
> go into the network stack.
> 
> The page_pool API offers buffer recycling capabilities for XDP but
> allocates one page per packet, unless the driver splits and manages
> the allocated page.
> This is a preliminary patch to add XDP support to mvneta driver
> 
> Tested-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> ---
>  drivers/net/ethernet/marvell/Kconfig  |  1 +
>  drivers/net/ethernet/marvell/mvneta.c | 76 ++++++++++++++++++++-------
>  2 files changed, 58 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/Kconfig b/drivers/net/ethernet/marvell/Kconfig
> index fb942167ee54..3d5caea096fb 100644
> --- a/drivers/net/ethernet/marvell/Kconfig
> +++ b/drivers/net/ethernet/marvell/Kconfig
> @@ -61,6 +61,7 @@ config MVNETA
>  	depends on ARCH_MVEBU || COMPILE_TEST
>  	select MVMDIO
>  	select PHYLINK
> +	select PAGE_POOL
>  	---help---
>  	  This driver supports the network interface units in the
>  	  Marvell ARMADA XP, ARMADA 370, ARMADA 38x and
> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> index 128b9fded959..8beae0e1eda7 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> @@ -37,6 +37,7 @@
>  #include <net/ip.h>
>  #include <net/ipv6.h>
>  #include <net/tso.h>
> +#include <net/page_pool.h>
>  
>  /* Registers */
>  #define MVNETA_RXQ_CONFIG_REG(q)                (0x1400 + ((q) << 2))
> @@ -603,6 +604,10 @@ struct mvneta_rx_queue {
>  	u32 pkts_coal;
>  	u32 time_coal;
>  
> +	/* page_pool */
> +	struct page_pool *page_pool;
> +	struct xdp_rxq_info xdp_rxq;
> +
>  	/* Virtual address of the RX buffer */
>  	void  **buf_virt_addr;
>  
> @@ -1815,19 +1820,12 @@ static int mvneta_rx_refill(struct mvneta_port *pp,
>  	dma_addr_t phys_addr;
>  	struct page *page;
>  
> -	page = __dev_alloc_page(gfp_mask);
> +	page = page_pool_alloc_pages(rxq->page_pool,
> +				     gfp_mask | __GFP_NOWARN);
>  	if (!page)
>  		return -ENOMEM;

Is the driver syncing the buffer somewhere else? (for_device)
If not you'll have to do this here. 

On a non-cache coherent machine (and i think this one is) you may get dirty
cache lines handed to the device. Those dirty cache lines might get written back
*after* the device has DMA'ed it's data. You need to flush those first to avoid
any data corruption

>  
> -	/* map page for use */
> -	phys_addr = dma_map_page(pp->dev->dev.parent, page, 0, PAGE_SIZE,
> -				 DMA_FROM_DEVICE);
> -	if (unlikely(dma_mapping_error(pp->dev->dev.parent, phys_addr))) {
> -		__free_page(page);
> -		return -ENOMEM;
> -	}
> -
> -	phys_addr += pp->rx_offset_correction;
> +	phys_addr = page_pool_get_dma_addr(page) + pp->rx_offset_correction;
>  	mvneta_rx_desc_fill(rx_desc, phys_addr, page, rxq);
>  	return 0;
>  }
> @@ -1894,10 +1892,11 @@ static void mvneta_rxq_drop_pkts(struct mvneta_port *pp,
>  		if (!data || !(rx_desc->buf_phys_addr))
>  			continue;
>  
> -		dma_unmap_page(pp->dev->dev.parent, rx_desc->buf_phys_addr,
> -			       PAGE_SIZE, DMA_FROM_DEVICE);
> -		__free_page(data);
> +		page_pool_put_page(rxq->page_pool, data, false);
>  	}
> +	if (xdp_rxq_info_is_reg(&rxq->xdp_rxq))
> +		xdp_rxq_info_unreg(&rxq->xdp_rxq);
> +	page_pool_destroy(rxq->page_pool);
>  }
>  
>  static void
> @@ -2029,8 +2028,7 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
>  				skb_add_rx_frag(rxq->skb, frag_num, page,
>  						frag_offset, frag_size,
>  						PAGE_SIZE);
> -				dma_unmap_page(dev->dev.parent, phys_addr,
> -					       PAGE_SIZE, DMA_FROM_DEVICE);
> +				page_pool_release_page(rxq->page_pool, page);
>  				rxq->left_size -= frag_size;
>  			}
>  		} else {
> @@ -2060,9 +2058,7 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
>  						frag_offset, frag_size,
>  						PAGE_SIZE);
>  
> -				dma_unmap_page(dev->dev.parent, phys_addr,
> -					       PAGE_SIZE, DMA_FROM_DEVICE);
> -
> +				page_pool_release_page(rxq->page_pool, page);
>  				rxq->left_size -= frag_size;
>  			}
>  		} /* Middle or Last descriptor */
> @@ -2829,11 +2825,53 @@ static int mvneta_poll(struct napi_struct *napi, int budget)
>  	return rx_done;
>  }
>  
> +static int mvneta_create_page_pool(struct mvneta_port *pp,
> +				   struct mvneta_rx_queue *rxq, int size)
> +{
> +	struct page_pool_params pp_params = {
> +		.order = 0,
> +		.flags = PP_FLAG_DMA_MAP,
> +		.pool_size = size,
> +		.nid = cpu_to_node(0),
> +		.dev = pp->dev->dev.parent,
> +		.dma_dir = DMA_FROM_DEVICE,
> +	};
> +	int err;
> +
> +	rxq->page_pool = page_pool_create(&pp_params);
> +	if (IS_ERR(rxq->page_pool)) {
> +		err = PTR_ERR(rxq->page_pool);
> +		rxq->page_pool = NULL;
> +		return err;
> +	}
> +
> +	err = xdp_rxq_info_reg(&rxq->xdp_rxq, pp->dev, 0);
> +	if (err < 0)
> +		goto err_free_pp;
> +
> +	err = xdp_rxq_info_reg_mem_model(&rxq->xdp_rxq, MEM_TYPE_PAGE_POOL,
> +					 rxq->page_pool);
> +	if (err)
> +		goto err_unregister_rxq;
> +
> +	return 0;
> +
> +err_unregister_rxq:
> +	xdp_rxq_info_unreg(&rxq->xdp_rxq);
> +err_free_pp:
> +	page_pool_destroy(rxq->page_pool);
> +	return err;
> +}
> +
>  /* Handle rxq fill: allocates rxq skbs; called when initializing a port */
>  static int mvneta_rxq_fill(struct mvneta_port *pp, struct mvneta_rx_queue *rxq,
>  			   int num)
>  {
> -	int i;
> +	int i, err;
> +
> +	err = mvneta_create_page_pool(pp, rxq, num);
> +	if (err < 0)
> +		return err;
>  
>  	for (i = 0; i < num; i++) {
>  		memset(rxq->descs + i, 0, sizeof(struct mvneta_rx_desc));
> -- 
> 2.21.0
> 


Thanks
/Ilias