netdev - Re: TCP and reordering

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Message-ID: <1354119695.21562.72.camel@shinybook.infradead.org>
Date:	Wed, 28 Nov 2012 16:21:35 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Vijay Subramanian <subramanian.vijay@...il.com>,
	David Miller <davem@...emloft.net>, saku@...i.fi,
	rick.jones2@...com, netdev@...r.kernel.org
Subject: Re: TCP and reordering

On Wed, 2012-11-28 at 08:09 -0800, Eric Dumazet wrote:
> My point was that if you limit number of in flight packet to 1,
> its relatively easy to add glue in the priv dev data, so that you chain
> the destructor without adding yet another fields in all skbs.

Hm, true. I do think we'll need to be able to have at least two packets
in-flight though. There's a fair amount of network stack to be navigated
by a skb once we release it, in the PPPoE and especially L2TP cases. The
latency involved in that, if we only allow one packet at a time, will
surely be noticeable. You're basically guaranteeing that a 'TX done' IRQ
won't have another packet in the device's queue ready to send, and you
won't be able to saturate the uplink.

I suppose your principle applies even for more than one skb at a time;
we can have an array of {skb, old_destructor} tuples in our per-channel
private state, rather than having to keep it with the skb itself... but
that's slightly less simple.

I'll go and knock something up...

-- 
dwmw2

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