netdev - how to make sure that packet is inserted into PACKET_MMAP ring buffer strictly according to its timestamp order?

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Date:	Wed, 22 Dec 2010 12:33:40 +0800
From:	Rui <wirelesser@...il.com>
To:	netdev@...r.kernel.org
Subject: how to make sure that packet is inserted into PACKET_MMAP ring buffer
 strictly according to its timestamp order?

hi

how to make sure that packet is inserted into PACKET_MMAP ring buffer
strictly according to its timestamp order?

I am studying the code below
as the function tpacket_rcv will be running in parallel in multi queue
nic supportted kernel,
is it possible that a later packet get the spinlock earlier,
thus it is copied to the ring buffer prior to packet which timestamp is earlier?

thanks
rui

af_packet.c
static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
		       struct packet_type *pt, struct net_device *orig_dev)
{
...
spin_lock(&sk->sk_receive_queue.lock);
	h.raw = packet_current_frame(po, &po->rx_ring, TP_STATUS_KERNEL);
	if (!h.raw)
		goto ring_is_full;
	packet_increment_head(&po->rx_ring);
	po->stats.tp_packets++;
	if (copy_skb) {
		status |= TP_STATUS_COPY;
		__skb_queue_tail(&sk->sk_receive_queue, copy_skb);
	}
	if (!po->stats.tp_drops)
		status &= ~TP_STATUS_LOSING;
	spin_unlock(&sk->sk_receive_queue.lock);

	skb_copy_bits(skb, 0, h.raw + macoff, snaplen);
}
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