netdev - Re: [PATCH net-next] net: netdev_alloc_skb() use build

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Message-ID: <1338815213.2760.1806.camel@edumazet-glaptop>
Date:	Mon, 04 Jun 2012 15:06:53 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Willy Tarreau <w@....eu>, David Miller <davem@...emloft.net>,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: netdev_alloc_skb() use build_skb()

On Mon, 2012-06-04 at 15:37 +0300, Michael S. Tsirkin wrote:
> On Thu, May 17, 2012 at 07:34:16PM +0200, Eric Dumazet wrote:
> > From: Eric Dumazet <edumazet@...gle.com>
> > 
> > Please note I havent tested yet this patch, lacking hardware for this.
> > 
> > (tg3/bnx2/bnx2x use build_skb, r8169 does a copy of incoming frames,
> > ixgbe uses fragments...)
> 
> virtio-net uses netdev_alloc_skb but maybe it should call
> build_skb instead?
> 
> Also, it's not uncommon for drivers to copy short packets out to be able
> to reuse pages.  virtio does this but I am guessing the logic is not
> really virtio specific.
> 
> We could do
> 	if (len < GOOD_COPY_LEN)
> 		netdev_alloc_skb
> 		memmov
> 	else
> 		build_skb
> 
> but maybe it makes sense to put this logic in build_skb?
> 
> 

I am not sure to understand the question.

If virtio-net uses netdev_alloc_skb(), all is good, you have nothing to
change.

build_skb() is for drivers that allocate the memory to hold frame, and
wait for NIC completion before allocating/populating the skb itself.



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