netdev - Re: [RFC] netem: de-GSO packets before enqueing

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Message-ID: <20120113112028.4a24d988@nehalam.linuxnetplumber.net>
Date:	Fri, 13 Jan 2012 11:20:28 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	Ben Hutchings <bhutchings@...arflare.com>,
	netdev <netdev@...r.kernel.org>,
	netfilter-devel <netfilter-devel@...r.kernel.org>
Subject: Re: [RFC] netem:  de-GSO packets before enqueing

On Fri, 13 Jan 2012 16:54:57 +0100
Eric Dumazet <eric.dumazet@...il.com> wrote:

> Le jeudi 12 janvier 2012 à 16:57 -0800, Stephen Hemminger a écrit :
> > Probably something like this is needed (untested).
> > 
> > This issue was discovered when looking at the skb_checksum path for the
> > netem corruption operation, but it is a general problem.
> > Network emulation operations like corruption and drop want to operate
> > on a per-packet (not per-segment) basis. This patch does GSO in software
> > if necessary to break up packets.  Code is similar to logic in xfrm_output.
> > 
> > Although it appears that the operation is not work conserving, it is okay
> > because the higher level qdisc operations account for packets by incrementing
> > by gso_size.
> 
> gso_size ok, but what about qlen ?
> 
> We end up splitting one GSO skb in multiple segments, but shouldnt we
> instruct upper qdisc(s) that qlen was increased, sort of
> qdisc_tree_increase_qlen() call ?
> 
> 
> 

Also, does pkt_len need to be set in cb after de-gso?
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