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

[David Miller <davem@davemloft.net>]

From: Alexei Starovoitov <ast@plumgrid.com>
Date: Mon, 13 Jul 2015 15:26:46 -0700

> On 7/13/15 1:55 PM, Daniel Borkmann wrote:
>> On 07/13/2015 10:17 PM, Alexei Starovoitov wrote:
>> ...
>>> We cannot check tc actions from pktgen, since they can be added
>>> dynamically.
>>> So I see three options:
>>> 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.

>>> 2 add unlikely(skb_shread) check to few tc actions
>>> 3 do nothing
> ...
>> pktgen case. :/ With regards to option 2, you could hide that behind
>> a static inline helper wrapped in IS_ENABLED(CONFIG_NET_PKTGEN), but
>> that is a veeeery ugly workaround/hack as well (and distros might
>> even ship it nevertheless).
> 
> naming such helper is a headache as well.
> static inline bool is_pktgen_shared_skb(struct sk_buff *skb)
> {
> #if IS_ENABLED(CONFIG_NET_PKTGEN)

As mentioned by others, this ifdef accomplishes nothing as indeed
every distribution turns pktgen on so %99.9999 of all users will not
benefit from this optimized check.