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

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Date:	Sat, 14 Jan 2012 17:06:46 +0100
From:	Hagen Paul Pfeifer <hagen@...u.net>
To:	Stephen Hemminger <shemminger@...tta.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

* Stephen Hemminger | 2012-01-12 16:57:20 [-0800]:

>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.

Thanks Stephen! Corruption is currently unusable if GSO is enabled. We disable
GSO/TSO on all our test machines therefore.

I have a larger set of patches for the corruption option for this merge
window. We will now test your patch (and the hopefully following qdisc len
updated patch).

Hagen
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