netdev - Re: [PATCH net-next] tc: fix tc actions in case of shared skb

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Message-ID: <55A59657.2050100@plumgrid.com>
Date:	Tue, 14 Jul 2015 16:08:07 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	David Miller <davem@...emloft.net>
Cc:	daniel@...earbox.net, jhs@...atatu.com, jiri@...nulli.us,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] tc: fix tc actions in case of shared skb

On 7/14/15 3:34 PM, David Miller wrote:
>>>> 1 get rid of burst hack for both RX and TX in pktgen (kills
>>>> >>>performance)
> #1 is a serious consideration if you don't come up with better ideas,
> since an optimization is for nothing if it knowingly breaks things.

I've dug up the pktgen source from 2002 and see:
   atomic_inc(&skb->users);
   odev->hard_start_xmit(skb, odev);
so it did this trick forever.
Looks like it's a fundamental way how pktgen was working
and working still. Even when new 'burst' feature is not used,
pktgen still increments skb->users to hold skb.
At present I don't have good ideas how to redesign pktgen
and since apparently no one noticed this tc_action+pktgen
breakage for years, it's probably ok to leave everything as-is until
better ideas come. I'm not giving up yet. Just ran out of ideas.

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