Subject: Re: [net PATCH] atl1c: Fix misuse of netdev_alloc_skb in refilling rx ring

From: Luis Henriques <[email-masked]>
Date: Tue, 30 Jul 2013 09:53:02 +0100

Eric Dumazet <[email-masked]> writes:

> From: Eric Dumazet <[email-masked]>
>
> On Mon, 2013-07-29 at 08:30 -0700, Eric Dumazet wrote:
>> On Mon, 2013-07-29 at 13:09 +0100, Luis Henriques wrote:
>> 
>> > 
>> > I confirm that I can't reproduce the issue using this patch.
>> > 
>> 
>> Thanks, I'll send a polished patch, as this one had an error if
>> build_skb() returns NULL (in case sk_buff allocation fails)
>
> Please try the following patch : It should use 2K frags instead of 4K
> for normal 1500 mtu

This patch seems to work fine as well -- I'm unable to reproduce the
issue.

Cheers,
-- 
Luis

>
> Thanks !
>
> [PATCH] atl1c: use custom skb allocator
>
> We had reports ( https://bugzilla.kernel.org/show_bug.cgi?id=54021 )
> that using high order pages for skb allocations is problematic for atl1c
>
> We do not know exactly what the problem is, but we suspect that crossing
> 4K pages is not well supported by this hardware.
>
> Use a custom allocator, using page allocator and 2K fragments for
> optimal stack behavior. We might make this allocator generic
> in future kernels.
>
> Signed-off-by: Eric Dumazet <[email-masked]>
> Cc: Luis Henriques <[email-masked]>
> Cc: Neil Horman <[email-masked]>
> ---
>  drivers/net/ethernet/atheros/atl1c/atl1c.h      |    3 +
>  drivers/net/ethernet/atheros/atl1c/atl1c_main.c |   40 +++++++++++++-
>  2 files changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/atheros/atl1c/atl1c.h b/drivers/net/ethernet/atheros/atl1c/atl1c.h
> index b2bf324..0f05565 100644
> --- a/drivers/net/ethernet/atheros/atl1c/atl1c.h
> +++ b/drivers/net/ethernet/atheros/atl1c/atl1c.h
> @@ -520,6 +520,9 @@ struct atl1c_adapter {
>  	struct net_device   *netdev;
>  	struct pci_dev      *pdev;
>  	struct napi_struct  napi;
> +	struct page         *rx_page;
> +	unsigned int	    rx_page_offset;
> +	unsigned int	    rx_frag_size;
>  	struct atl1c_hw        hw;
>  	struct atl1c_hw_stats  hw_stats;
>  	struct mii_if_info  mii;    /* MII interface info */
> diff --git a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> index 786a874..a36a760 100644
> --- a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> +++ b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> @@ -481,10 +481,15 @@ static int atl1c_set_mac_addr(struct net_device *netdev, void *p)
>  static void atl1c_set_rxbufsize(struct atl1c_adapter *adapter,
>  				struct net_device *dev)
>  {
> +	unsigned int head_size;
>  	int mtu = dev->mtu;
>  
>  	adapter->rx_buffer_len = mtu > AT_RX_BUF_SIZE ?
>  		roundup(mtu + ETH_HLEN + ETH_FCS_LEN + VLAN_HLEN, 8) : AT_RX_BUF_SIZE;
> +
> +	head_size = SKB_DATA_ALIGN(adapter->rx_buffer_len + NET_SKB_PAD) +
> +		    SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> +	adapter->rx_frag_size = roundup_pow_of_two(head_size);
>  }
>  
>  static netdev_features_t atl1c_fix_features(struct net_device *netdev,
> @@ -952,6 +957,10 @@ static void atl1c_free_ring_resources(struct atl1c_adapter *adapter)
>  		kfree(adapter->tpd_ring[0].buffer_info);
>  		adapter->tpd_ring[0].buffer_info = NULL;
>  	}
> +	if (adapter->rx_page) {
> +		put_page(adapter->rx_page);
> +		adapter->rx_page = NULL;
> +	}
>  }
>  
>  /**
> @@ -1639,6 +1648,35 @@ static inline void atl1c_rx_checksum(struct atl1c_adapter *adapter,
>  	skb_checksum_none_assert(skb);
>  }
>  
> +static struct sk_buff *atl1c_alloc_skb(struct atl1c_adapter *adapter)
> +{
> +	struct sk_buff *skb;
> +	struct page *page;
> +
> +	if (adapter->rx_frag_size > PAGE_SIZE)
> +		return netdev_alloc_skb(adapter->netdev,
> +					adapter->rx_buffer_len);
> +
> +	page = adapter->rx_page;
> +	if (!page) {
> +		adapter->rx_page = page = alloc_page(GFP_ATOMIC);
> +		if (unlikely(!page))
> +			return NULL;
> +		adapter->rx_page_offset = 0;
> +	}
> +
> +	skb = build_skb(page_address(page) + adapter->rx_page_offset,
> +			adapter->rx_frag_size);
> +	if (likely(skb)) {
> +		adapter->rx_page_offset += adapter->rx_frag_size;
> +		if (adapter->rx_page_offset >= PAGE_SIZE)
> +			adapter->rx_page = NULL;
> +		else
> +			get_page(page);
> +	}
> +	return skb;
> +}
> +
>  static int atl1c_alloc_rx_buffer(struct atl1c_adapter *adapter)
>  {
>  	struct atl1c_rfd_ring *rfd_ring = &adapter->rfd_ring;
> @@ -1660,7 +1698,7 @@ static int atl1c_alloc_rx_buffer(struct atl1c_adapter *adapter)
>  	while (next_info->flags & ATL1C_BUFFER_FREE) {
>  		rfd_desc = ATL1C_RFD_DESC(rfd_ring, rfd_next_to_use);
>  
> -		skb = netdev_alloc_skb(adapter->netdev, adapter->rx_buffer_len);
> +		skb = atl1c_alloc_skb(adapter);
>  		if (unlikely(!skb)) {
>  			if (netif_msg_rx_err(adapter))
>  				dev_warn(&pdev->dev, "alloc rx buffer failed\n");
>