netdev - Re: [PATCH net-next-2.6] net: Introduce skb_orphan

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Date:	Thu, 22 Apr 2010 09:47:03 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next-2.6] net: Introduce skb_orphan_try()

Le jeudi 22 avril 2010 à 00:41 -0700, David Miller a écrit :
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Thu, 22 Apr 2010 09:33:57 +0200
> 
> > Le jeudi 22 avril 2010 à 00:26 -0700, David Miller a écrit :
> >> @@ -1865,6 +1865,7 @@ static int dev_gso_segment(struct sk_buff *skb)
> >>  	int features = dev->features & ~(illegal_highdma(dev, skb) ?
> >>  					 NETIF_F_SG : 0);
> >>  
> >> +	skb_orphan_try(skb);
> >>  	segs = skb_gso_segment(skb, features);
> >>  
> >>  	/* Verifying header integrity only. */
> > 
> > Yes, it seems better.
> > 
> > What about the 
> > 
> > if (dev->priv_flags & IFF_XMIT_DST_RELEASE)
> > 	skb_dst_drop(skb);
> > 
> > This thing might also be moved before the split, since split probably
> > clone all dst ?
> 
> Good catch, agreed.
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 3ba774b..4f897e2 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1851,6 +1851,17 @@ static void dev_gso_skb_destructor(struct sk_buff *skb)
>  		cb->destructor(skb);
>  }
>  
> +/*
> + * Try to orphan skb early, right before transmission by the device.
> + * We cannot orphan skb if tx timestamp is requested, since
> + * drivers need to call skb_tstamp_tx() to send the timestamp.
> + */
> +static inline void skb_orphan_try(struct sk_buff *skb)
> +{
> +	if (!skb_tx(skb)->flags)
> +		skb_orphan(skb);
> +}
> +
>  /**
>   *	dev_gso_segment - Perform emulated hardware segmentation on skb.
>   *	@skb: buffer to segment
> @@ -1865,6 +1876,7 @@ static int dev_gso_segment(struct sk_buff *skb)
>  	int features = dev->features & ~(illegal_highdma(dev, skb) ?
>  					 NETIF_F_SG : 0);
>  
> +	skb_orphan_try(skb);
>  	segs = skb_gso_segment(skb, features);
>  
>  	/* Verifying header integrity only. */
> @@ -1881,17 +1893,6 @@ static int dev_gso_segment(struct sk_buff *skb)
>  	return 0;
>  }
>  
> -/*
> - * Try to orphan skb early, right before transmission by the device.
> - * We cannot orphan skb if tx timestamp is requested, since
> - * drivers need to call skb_tstamp_tx() to send the timestamp.
> - */
> -static inline void skb_orphan_try(struct sk_buff *skb)
> -{
> -	if (!skb_tx(skb)->flags)
> -		skb_orphan(skb);
> -}
> -
>  int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
>  			struct netdev_queue *txq)
>  {
> @@ -1902,13 +1903,6 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
>  		if (!list_empty(&ptype_all))
>  			dev_queue_xmit_nit(skb, dev);
>  
> -		if (netif_needs_gso(dev, skb)) {
> -			if (unlikely(dev_gso_segment(skb)))
> -				goto out_kfree_skb;
> -			if (skb->next)
> -				goto gso;
> -		}
> -
>  		/*
>  		 * If device doesnt need skb->dst, release it right now while
>  		 * its hot in this cpu cache
> @@ -1916,6 +1910,13 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
>  		if (dev->priv_flags & IFF_XMIT_DST_RELEASE)
>  			skb_dst_drop(skb);
>  
> +		if (netif_needs_gso(dev, skb)) {
> +			if (unlikely(dev_gso_segment(skb)))
> +				goto out_kfree_skb;
> +			if (skb->next)
> +				goto gso;
> +		}
> +
>  		skb_orphan_try(skb);
>  		rc = ops->ndo_start_xmit(skb, dev);
>  		if (rc == NETDEV_TX_OK)

You could have one skb_orphan_try() call before the

if (netif_needs_gso(dev, skb)) {

and remove it from dev_gso_segment() ?


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