netdev - Re: [net-next RFC] pktgen: don't wait for the device who doesn't free skb immediately after sent

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Message-ID: <20121126093728.0a10f97f@nehalam.linuxnetplumber.net>
Date:	Mon, 26 Nov 2012 09:37:28 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	rusty@...tcorp.com.au, mst@...hat.com, davem@...emloft.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [net-next RFC] pktgen: don't wait for the device who doesn't
 free skb immediately after sent

On Mon, 26 Nov 2012 15:56:52 +0800
Jason Wang <jasowang@...hat.com> wrote:

> Some deivces do not free the old tx skbs immediately after it has been sent
> (usually in tx interrupt). One such example is virtio-net which optimizes for
> virt and only free the possible old tx skbs during the next packet sending. This
> would lead the pktgen to wait forever in the refcount of the skb if no other
> pakcet will be sent afterwards.
> 
> Solving this issue by introducing a new flag IFF_TX_SKB_FREE_DELAY which could
> notify the pktgen that the device does not free skb immediately after it has
> been sent and let it not to wait for the refcount to be one.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Another alternative would be using skb_orphan() and skb->destructor.
There are other cases where skb's are not freed right away.
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