Re: [dpdk-dev] Unable to configure ethdev in secondary process using ring PMD

[Alexey Bogdanenko <abogdanenko@ecotelecom.ru>]

On 11/30/2015 07:53 PM, Richardson, Bruce wrote:
>
>
>> -----Original Message-----
>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Alexey Bogdanenko
>> Sent: Monday, November 30, 2015 4:17 PM
>> To: dev@dpdk.org
>> Subject: [dpdk-dev] Unable to configure ethdev in secondary process using
>> ring PMD
>>
>> Hello,
>>
>> I would like to setup communication between two existing DPDK applications
>> and run them on the same host.
>>
>> "Connecting their ports" in some way in order not to rewrite the
>> applications would be very desirable. Specifically, I would like one
>> process to send packets and the second process to receive the packets
>> using rte_eth_tx_burst() and rte_eth_rx_burst() respectively.
>>
>> The most straightforward way to accomplish this seems to be by using ring
>> based PMD API as described in the documentation [1] and email [2].
>> To adapt the example from the documentation to multi-process scenario, I
>> call rte_ring_create() and rte_eth_from_rings() in the primary process,
>> rte_ring_lookup() and rte_eth_from_rings() in the secondary process.
>> After that each process calls rte_eth_dev_configure().
>>
>> Unfortunately, the function returns -1001 in the secondary process, which
>> is explained in debug log:
>>
>> PMD: rte_eth_dev_configure: Cannot run in secondary processes
>>
>> Is it possible to connect the applications as described above? Any advice
>> would be appreciated.
>>
>> References:
>>
>> 1. Network Interface Controller Drivers. Chapter 8.
>> Libpcap and Ring Based Poll Mode Drivers.
>>
>> 2. DPDK ML. Fri Dec 6 07:22:06 CET 2013. How to know corresponding device
>> from port number. Tetsuya.Mukawa
>>
>> Thanks,
>>
>> Alexey Bogdanenko
>
> Hi Alexey,
>
> The ring PMDs returned from eth_from_rings should be all ready to be used without having to explicitly configure it or set up the queues.
>
> /Bruce
>

Thanks for the quick reply,

I updated dpdk from v2.1.0 to a more recent version (near v2.2.0-rc2), 
removed calls to rte_eth_dev_configure(), rte_eth_rx_queue_setup(). It 
solved the problem.

Your advice was very helpful.

However, I encountered a rather minor but similar issue, which is that
rte_eth_dev_start() returns -1001 in the secondary processes. The 
message I get is:

rte_eth_dev_start: Cannot run in secondary processes

Now, I could avoid calling the function altogether, however in this case
rte_eth_link_get_nowait() reports that the link status is down which is 
a bit inconvenient.

Did I miss anything or is it just a limitation of ring PMD?

Alexey Bogdanenko