netdev - sunvnet and ->xmit

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Message-Id: <20141007.151849.84417269004453869.davem@davemloft.net>
Date:	Tue, 07 Oct 2014 15:18:49 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	netdev@...r.kernel.org
CC:	david.stevens@...cle.com, Raghuram.Kothakota@...cle.com,
	sowmini.varadhan@...cle.com
Subject: sunvnet and ->xmit_more

David and others working on sunvnet, I just wanted to point out that
in the net-next tree there is a new facility that can improve
performance quite a bit in sunvnet.

Basically in the ->ndo_start_xmit() handler, if you see skb->xmit_more
set then the stack is telling you that it guarentees that another
packet will be given to you immediately when ->ndo_start_xmit()
returns.

This means that, unless you have filled up your TX queue, you can
defer the TX indication to the device.

For example, in the virtio_net driver the test is:

	if (__netif_subqueue_stopped(dev, qnum) || !skb->xmit_more)
		virtqueue_kick(sq->vq);

The pktgen module also has a new "burst" parameter you can use to test
out this facility directly, and the qdisc layer has heuristics for
dequeueing multiple packets at a time for normal traffic.

Just FYI...
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