Subject: Re: [patch net-next RFC v3 10/10] openvswitch: add support for datapath hardware offload

From: John Fastabend <[email-masked]>
Date: Thu, 24 Apr 2014 08:58:32 -0700

On 4/24/2014 8:46 AM, Jiri Pirko wrote:
> Thu, Apr 24, 2014 at 04:54:19PM CEST, [email-masked] wrote:
>> On 04/17/2014 05:15 AM, Jiri Pirko wrote:
>>> Benefit from the possibility to work with flows in switch devices and
>>> use the swdev api to offload flow datapath.
>>>
>>> Signed-off-by: Jiri Pirko <[email-masked]>
>>> ---
>>
>>
>> [...]
>>
>>>
>>> @@ -840,13 +841,15 @@ static int ovs_flow_cmd_new_or_set(struct sk_buff *skb, struct genl_info *info)
>>>   		flow->flow.key = masked_key;
>>>   		flow->flow.unmasked_key = key;
>>>   		rcu_assign_pointer(flow->sf_acts, acts);
>>> +		acts = NULL;
>>>
>>>   		/* Put flow in bucket. */
>>>   		error = ovs_flow_tbl_insert(&dp->table, flow, &mask);
>>> -		if (error) {
>>> -			acts = NULL;
>>> +		if (error)
>>>   			goto err_flow_free;
>>> -		}
>>> +		error = ovs_hw_flow_insert(dp, flow, flow->sf_acts);
>>> +		if (error)
>>> +			goto err_flow_tbl_remove;
>>>
>>>   		reply = ovs_flow_cmd_build_info(flow, dp, info, OVS_FLOW_CMD_NEW);
>>>   	} else {
>>
>> Hi Jiri,
>>
>> If I read this correctly it looks like you do a insert into software
>> flow tables and then an insert into the hardware flow tables. Into
>> all lowerdevs. Let me know if I got this wrong.
>
> It should be sufficient to use one-port-per-switch to insert this. I
> just insert it to all and if 2 ports of the same switch are used the
> switch should see that the flow is already there and bail out. This is
> rough so far. Needs some polishing.
> 		
>

OK that seems fine.

>>
>> This might break on some rules (an insert tag for example) and also
>> underutilize the switch resources by pushing rules into the switch that
>> we really only need in software tables or maybe only on some set of
>> ports.
>
> I thought that I would introduce a flag that would say "push this flow
> to hw".
>

Great this would align with how the FDB interface works. I think this
is a good model although I would prefer a bitfield so I can push it
to hardware, or sw, or both.

>>
>> I think we need to allow applications direct access to the flow table
>> via netlink so I can write my policy in user space and not require
>> OVS. If OVS wants to support a mode where it does this automagically
>> it can support it in userspace and the kernel side does not need to
>> change.
>
> The idea was to use the existing ovs api for this so it would be smooth
> to userspace. For non-ovs usage there is certainly possible to introduce
> new iface which would just call same ndos.
>

If we get a bitfield to push to just hardware and just software then
using the OVS interface is probably ok. We also need someway to expose
capabilities.

Anyways not a bad start. We can clean it up when the hardware support
is ready.

.John