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

From: Lorenzo Bianconi <[email-masked]>
Date: Mon, 7 Oct 2019 14:27:57 +0200

> Hi Lorenzo, 

Hi Ilias,

> 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 <[email-masked]>
> > Signed-off-by: Ilias Apalodimas <[email-masked]>
> > Signed-off-by: Jesper Dangaard Brouer <[email-masked]>
> > Signed-off-by: Lorenzo Bianconi <[email-masked]>
> > ---
> >  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. 

ack, I will add a dma_sync_to_device() in v2, thx for the hint :)

> 
> 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

Right.

Regards,
Lorenzo

> 
> >  
> > -	/* 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