netdev - Re: [RFC v1] hand off skb list to other cpu to submit to upper layer

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Date:	Wed, 04 Mar 2009 01:39:37 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	yanmin_zhang@...ux.intel.com
Cc:	herbert@...dor.apana.org.au, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, jesse.brandeburg@...el.com,
	shemminger@...tta.com
Subject: Re: [RFC v1] hand off skb list to other cpu to submit to upper
 layer

From: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Date: Wed, 04 Mar 2009 17:27:48 +0800

> Both the new skb_record_rx_queue and current kernel have an
> assumption on multi-queue. The assumption is it's best to send out
> packets from the TX of the same number of queue like the one of RX
> if the receved packets are related to the out packets. Or more
> direct speaking is we need send packets on the same cpu on which we
> receive them. The start point is that could reduce skb and data
> cache miss.

We have to use the same TX queue for all packets for the same
connection flow (same src/dst IP address and ports) otherwise
we introduce reordering.

Herbert brought this up, now I have explicitly brought this up,
and you cannot ignore this issue.

You must not knowingly reorder packets, and using different TX
queues for packets within the same flow does that.
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