netdev - Re: [PATCH net-next] net: openvswitch: Set OvS recirc

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Date:   Tue, 20 Aug 2019 07:08:13 +0000
From:   Paul Blakey <paulb@...lanox.com>
To:     Pravin Shelar <pshelar@....org>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
CC:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Justin Pettit <jpettit@...ira.com>,
        Simon Horman <simon.horman@...ronome.com>,
        Vlad Buslov <vladbu@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>, Roi Dayan <roid@...lanox.com>,
        Yossi Kuperman <yossiku@...lanox.com>,
        Rony Efraim <ronye@...lanox.com>, Oz Shlomo <ozsh@...lanox.com>
Subject: Re: [PATCH net-next] net: openvswitch: Set OvS recirc_id from tc
 chain


On 8/20/2019 8:50 AM, Pravin Shelar wrote:
> On Mon, Aug 19, 2019 at 10:42 AM Marcelo Ricardo Leitner
> <marcelo.leitner@...il.com> wrote:
>> On Sun, Aug 18, 2019 at 07:00:59PM +0300, Paul Blakey wrote:
>>> What do you guys say about the following diff on top of the last one?
>>> Use static key, and also have OVS_DP_CMD_SET command probe/enable the feature.
>>>
>>> This will allow userspace to probe the feature, and selectivly enable it via the
>>> OVS_DP_CMD_SET command.
>> I'm not convinced yet that we need something like this. Been
>> wondering, skb_ext_find() below is not that expensive if not in use.
>> It's just a bit check and that's it, it returns NULL.
>>
>> And drivers will only be setting this if they have tc-offloading
>> enabled (assuming they won't be seeing it for chain 0 all the time).
>> On which case, with tc offloading, we need this in order to work
>> properly.
>>
>> Is the bit checking really that worrysome?
>>
> Point is this would be completely unnecessary check for software only
> cases, that is what static key is used for, when you have a feature in
> datapath that is not used by majority of users. So I do not see any
> downside of having this static key.

Also it's good that I can now probe kernel support via OVS_DP_CMD_SET.

Since user can disable the kernel support or even use a different 
version of the datapath module, it would silently bug on misses from tc.

Now I can set the recirc sharing feature in user_feature via SET op, and 
check the returned new user_features or an error code.

If no error, and user_features contains the flag (won't be there for 
older DPs that won't return error), then DP supports this feature and

kernel config is enabled.