Re: [PATCHv3 net-next 11/12] net: mvpp2: switch to build_skb() in the RX path

[Marcin Wojtas]

Hi Thomas,

How about switching to napi_alloc_frag() in mvpp2_rx_refill(), which
is called in hotpath? In easy way, it may give some performance gain.

Best regards,
Marcin

2017-02-02 16:51 GMT+01:00 Thomas Petazzoni
:
> This commit adapts the mvpp2 RX path to use the build_skb() method. Not
> only build_skb() is now the recommended mechanism, but it also
> simplifies the addition of support for the PPv2.2 variant.
>
> Indeed, without build_skb(), we have to keep track for each RX
> descriptor of the physical address of the packet buffer, and the virtual
> address of the SKB. However, in PPv2.2 running on 64 bits platform,
> there is not enough space in the descriptor to store the virtual address
> of the SKB. So having to take care only of the address of the packet
> buffer, and building the SKB upon reception helps in supporting PPv2.2.
>
> The implementation is fairly straightforward:
>
>  - mvpp2_skb_alloc() is renamed to mvpp2_buf_alloc() and no longer
>allocates a SKB. Instead, it allocates a buffer using the new
>mvpp2_frag_alloc() function, with enough space for the data and SKB.
>
>  - The initialization of the RX buffers in mvpp2_bm_bufs_add() as well
>as the refill of the RX buffers in mvpp2_rx_refill() is adjusted
>accordingly.
>
>  - Finally, the mvpp2_rx() is modified to use build_skb().
>
> Signed-off-by: Thomas Petazzoni 
> ---
>  drivers/net/ethernet/marvell/mvpp2.c | 77 
> +---
>  1 file changed, 55 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/net/ethernet/marvell/mvpp2.c 
> b/drivers/net/ethernet/marvell/mvpp2.c
> index ec8f452..4132dc8 100644
> --- a/drivers/net/ethernet/marvell/mvpp2.c
> +++ b/drivers/net/ethernet/marvell/mvpp2.c
> @@ -918,6 +918,7 @@ struct mvpp2_bm_pool {
> int buf_size;
> /* Packet size */
> int pkt_size;
> +   int frag_size;
>
> /* BPPE virtual base address */
> u32 *virt_addr;
> @@ -3354,6 +3355,22 @@ static void mvpp2_cls_oversize_rxq_set(struct 
> mvpp2_port *port)
> mvpp2_write(port->priv, MVPP2_CLS_SWFWD_PCTRL_REG, val);
>  }
>
> +static void *mvpp2_frag_alloc(const struct mvpp2_bm_pool *pool)
> +{
> +   if (likely(pool->frag_size <= PAGE_SIZE))
> +   return netdev_alloc_frag(pool->frag_size);
> +   else
> +   return kmalloc(pool->frag_size, GFP_ATOMIC);
> +}
> +
> +static void mvpp2_frag_free(const struct mvpp2_bm_pool *pool, void *data)
> +{
> +   if (likely(pool->frag_size <= PAGE_SIZE))
> +   skb_free_frag(data);
> +   else
> +   kfree(data);
> +}
> +
>  /* Buffer Manager configuration routines */
>
>  /* Create pool */
> @@ -3428,7 +3445,8 @@ static void mvpp2_bm_bufs_free(struct device *dev, 
> struct mvpp2 *priv,
>
> if (!vaddr)
> break;
> -   dev_kfree_skb_any((struct sk_buff *)vaddr);
> +
> +   mvpp2_frag_free(bm_pool, (void *)vaddr);
> }
>
> /* Update BM driver with number of buffers removed from pool */
> @@ -3542,29 +3560,28 @@ static void mvpp2_rxq_short_pool_set(struct 
> mvpp2_port *port,
> mvpp2_write(port->priv, MVPP2_RXQ_CONFIG_REG(prxq), val);
>  }
>
> -/* Allocate skb for BM pool */
> -static struct sk_buff *mvpp2_skb_alloc(struct mvpp2_port *port,
> -  struct mvpp2_bm_pool *bm_pool,
> -  dma_addr_t *buf_phys_addr,
> -  gfp_t gfp_mask)
> +static void *mvpp2_buf_alloc(struct mvpp2_port *port,
> +struct mvpp2_bm_pool *bm_pool,
> +dma_addr_t *buf_phys_addr,
> +gfp_t gfp_mask)
>  {
> -   struct sk_buff *skb;
> dma_addr_t phys_addr;
> +   void *data;
>
> -   skb = __dev_alloc_skb(bm_pool->pkt_size, gfp_mask);
> -   if (!skb)
> +   data = mvpp2_frag_alloc(bm_pool);
> +   if (!data)
> return NULL;
>
> -   phys_addr = dma_map_single(port->dev->dev.parent, skb->head,
> +   phys_addr = dma_map_single(port->dev->dev.parent, data,
>MVPP2_RX_BUF_SIZE(bm_pool->pkt_size),
> DMA_FROM_DEVICE);
> if (unlikely(dma_mapping_error(port->dev->dev.parent, phys_addr))) {
> -   dev_kfree_skb_any(skb);
> +   mvpp2_frag_free(bm_pool, data);
> return NULL;
> }
> *buf_phys_addr = phys_addr;
>
> -   return skb;
> +   return data;
>  }
>
>  /* Set pool number in a BM cookie */
> @@ -3620,9 +3637,9 @@ static void mvpp2_pool_refill(struct mvpp2_port *port, 
> u32 bm,
>  static int mvpp2_bm_bufs_add(struct mvpp2_port *port,
>  struct mvpp2_bm_pool *bm_pool, int buf_num)
>  {
> -   struct sk_buff *skb;
> int i, 

[PATCHv3 net-next 11/12] net: mvpp2: switch to build_skb() in the RX path

[Thomas Petazzoni]

This commit adapts the mvpp2 RX path to use the build_skb() method. Not
only build_skb() is now the recommended mechanism, but it also
simplifies the addition of support for the PPv2.2 variant.

Indeed, without build_skb(), we have to keep track for each RX
descriptor of the physical address of the packet buffer, and the virtual
address of the SKB. However, in PPv2.2 running on 64 bits platform,
there is not enough space in the descriptor to store the virtual address
of the SKB. So having to take care only of the address of the packet
buffer, and building the SKB upon reception helps in supporting PPv2.2.

The implementation is fairly straightforward:

 - mvpp2_skb_alloc() is renamed to mvpp2_buf_alloc() and no longer
   allocates a SKB. Instead, it allocates a buffer using the new
   mvpp2_frag_alloc() function, with enough space for the data and SKB.

 - The initialization of the RX buffers in mvpp2_bm_bufs_add() as well
   as the refill of the RX buffers in mvpp2_rx_refill() is adjusted
   accordingly.

 - Finally, the mvpp2_rx() is modified to use build_skb().

Signed-off-by: Thomas Petazzoni 
---
 drivers/net/ethernet/marvell/mvpp2.c | 77 +---
 1 file changed, 55 insertions(+), 22 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvpp2.c 
b/drivers/net/ethernet/marvell/mvpp2.c
index ec8f452..4132dc8 100644
--- a/drivers/net/ethernet/marvell/mvpp2.c
+++ b/drivers/net/ethernet/marvell/mvpp2.c
@@ -918,6 +918,7 @@ struct mvpp2_bm_pool {
int buf_size;
/* Packet size */
int pkt_size;
+   int frag_size;
 
/* BPPE virtual base address */
u32 *virt_addr;
@@ -3354,6 +3355,22 @@ static void mvpp2_cls_oversize_rxq_set(struct mvpp2_port 
*port)
mvpp2_write(port->priv, MVPP2_CLS_SWFWD_PCTRL_REG, val);
 }
 
+static void *mvpp2_frag_alloc(const struct mvpp2_bm_pool *pool)
+{
+   if (likely(pool->frag_size <= PAGE_SIZE))
+   return netdev_alloc_frag(pool->frag_size);
+   else
+   return kmalloc(pool->frag_size, GFP_ATOMIC);
+}
+
+static void mvpp2_frag_free(const struct mvpp2_bm_pool *pool, void *data)
+{
+   if (likely(pool->frag_size <= PAGE_SIZE))
+   skb_free_frag(data);
+   else
+   kfree(data);
+}
+
 /* Buffer Manager configuration routines */
 
 /* Create pool */
@@ -3428,7 +3445,8 @@ static void mvpp2_bm_bufs_free(struct device *dev, struct 
mvpp2 *priv,
 
if (!vaddr)
break;
-   dev_kfree_skb_any((struct sk_buff *)vaddr);
+
+   mvpp2_frag_free(bm_pool, (void *)vaddr);
}
 
/* Update BM driver with number of buffers removed from pool */
@@ -3542,29 +3560,28 @@ static void mvpp2_rxq_short_pool_set(struct mvpp2_port 
*port,
mvpp2_write(port->priv, MVPP2_RXQ_CONFIG_REG(prxq), val);
 }
 
-/* Allocate skb for BM pool */
-static struct sk_buff *mvpp2_skb_alloc(struct mvpp2_port *port,
-  struct mvpp2_bm_pool *bm_pool,
-  dma_addr_t *buf_phys_addr,
-  gfp_t gfp_mask)
+static void *mvpp2_buf_alloc(struct mvpp2_port *port,
+struct mvpp2_bm_pool *bm_pool,
+dma_addr_t *buf_phys_addr,
+gfp_t gfp_mask)
 {
-   struct sk_buff *skb;
dma_addr_t phys_addr;
+   void *data;
 
-   skb = __dev_alloc_skb(bm_pool->pkt_size, gfp_mask);
-   if (!skb)
+   data = mvpp2_frag_alloc(bm_pool);
+   if (!data)
return NULL;
 
-   phys_addr = dma_map_single(port->dev->dev.parent, skb->head,
+   phys_addr = dma_map_single(port->dev->dev.parent, data,
   MVPP2_RX_BUF_SIZE(bm_pool->pkt_size),
DMA_FROM_DEVICE);
if (unlikely(dma_mapping_error(port->dev->dev.parent, phys_addr))) {
-   dev_kfree_skb_any(skb);
+   mvpp2_frag_free(bm_pool, data);
return NULL;
}
*buf_phys_addr = phys_addr;
 
-   return skb;
+   return data;
 }
 
 /* Set pool number in a BM cookie */
@@ -3620,9 +3637,9 @@ static void mvpp2_pool_refill(struct mvpp2_port *port, 
u32 bm,
 static int mvpp2_bm_bufs_add(struct mvpp2_port *port,
 struct mvpp2_bm_pool *bm_pool, int buf_num)
 {
-   struct sk_buff *skb;
int i, buf_size, total_size;
dma_addr_t phys_addr;
+   void *buf;
 
buf_size = MVPP2_RX_BUF_SIZE(bm_pool->pkt_size);
total_size = MVPP2_RX_TOTAL_SIZE(buf_size);
@@ -3636,11 +3653,11 @@ static int mvpp2_bm_bufs_add(struct mvpp2_port *port,
}
 
for (i = 0; i < buf_num; i++) {
-   skb = mvpp2_skb_alloc(port, bm_pool, _addr, GFP_KERNEL);
-   if (!skb)
+   buf = mvpp2_buf_alloc(port, bm_pool, _addr, GFP_KERNEL);
+