Impact on DPDK application when using the multi-process feature?

[Stephen Hemminger]

On Fri, 26 Nov 2021 13:27:40 +0100
Staffan Wiklund <staffan491 at gmail.com> wrote:

> Hello
> 
> I wonder if you please can help me with some questions regarding the DPDK
> multi-process feature?
> 
> If a primary process and the secondary processes all execute on different
> CPU cores,
> what limitations are there on the secondary processes when using DPDK
> functions
> for initialization of EAL and for handling ethernet devices?
> 
> That is, is a secondary process allowed to call the rte_eal_init function
> or any of
> the rte_eth_xxx functions?


Secondary process has to call rte_eal_init() with secondary (or auto flag).
Which of the rte_eth_xxx functions are you asking about?

> What will happen if a secondary process calls any of these DPDK functions?
> 
> The reason for these questions is that I would like to execute 3-4 DPDK
> applications that
> now executes as stand-alone applications as one primary process and the
> other
> applications as secondary processes. All these processes will share memory
> which
> shall be used to improve the speed of communication between the
> applications.

Several applications do this.

> The applications currently use DPDK for Ethernet based communication and I
> would
> like to learn what needs to be modified in order to be able to execute them
> as a
> primary and secondary processes using DPDK shared memory.
> 
> Best regards
> Staffan

To be honest, my experience is that not all functions work on all drivers
with the multi-process model. The documentation mostly covers the ones that
don't but you have to be careful and test with particular drivers and use cases.