Re: [dpdk-dev] [PATCH] net/i40e: add a specific API to control the LLDP agent

[Thomas Monjalon <thomas@monjalon.net>]

21/05/2018 10:58, Laurent Hardy:
> Hello Thomas,
> 
> On 05/21/2018 10:39 AM, Thomas Monjalon wrote:
> > 21/05/2018 05:35, Zijie Pan:
> >>>> Add a new API rte_pmd_i40e_set_lldp_cmd to control LLDP agent for i40e.
> >>>> It supports the following i40e debug lldp commands:
> >>>>      - start/stop of the LLDP agent.
> >>>>      - get local/remote of the LLDP MIB (Management Information Base).
> >>>>
> >>>> Signed-off-by: Laurent Hardy <laurent.hardy@6wind.com>
> >>>> Signed-off-by: Zijie Pan <zijie.pan@6wind.com>
> >>> Does it mean that this feature is enabled by default in i40e devices?
> >>> Should it be disabled by default?
> >> The new API is just an interface to control the LLDP agent. No functions of i40e call it by default. It is only used to debug LLDP of i40e devices. For example we can add a new command for test-pmd to debug lldp of i40e by calling rte_pmd_i40e_set_lldp_cmd().
> > There is a command to stop the LLDP agent.
> > My question is to know whether this agent is running by default
> > and should be disabled?
> This agent is running by default.
> Beside, disabling LLDP agent when using old fw (NVM 4.53 or 5.x) could 
> have some side effects.
> 
> https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/xl710-10-40-controller-spec-update.pdf
> 
> Extracted from x710 intel spec:
> 
> "70. LLDP Disable Can Result in Incorrect Configuration of the Receive Packet Buffer
> 
> Problem:
> ---------
> The default operation of the device is LLDP enabled.
> LLDP can be disabled by an AQ command or by a custom NVM obtained from Intel.
> Disabling LLDP when using NVM 4.53 or 5.x can result in the device firmware not configuring the Receive Packet Buffer according to the link mode and flow control settings.
> Implication:
> ------------
> If flow control is disabled, a hang of the receive data path could occur wherein all received packets are dropped.
> If flow control is enabled, the incorrect settings could cause packet drops despite the flow control, making the flow control ineffective.
> Also, throughput might be sub-optimal in some cases.
> Workaround:
> -----------
> When using NVM 4.53 or 5.x, do one of the following:
> •  Do not disable LLDP or DCBx. Leave the device in default operation mode.
> •  Use the Set Local LLDP MIB admin queue command to apply the (default) DCB configuration during driver initialization and following any link-up event.
> When using NVM 6.01 or later, the receive data path does not hang even if the FW LLDP is disabled."

OK, interesting, thank you.

I think you should add a comment in the code to explain why it is not disabled.
And later, we could consider disabling it with new firmwares.


> > I mean i40e is generating LLDP packets by default?

So the answer is yes, i40e generates packets silently :)