[dpdk-dev] DPDK and forked processes

["Eads, Gage" <gage.eads@intel.com>]

Hi all,

Does DPDK support forking secondary processes after executing rte_eal_init()? The l2fwd_fork example and at least one application (OpenEM: https://sourceforge.net/projects/eventmachine/) use this model, and they do so by fixing up the EAL internals (e.g. manually changing process_type from primary to secondary) at the start of the child process. This feels like a hack, and I can't find any documentation describing this model.

Moreover, this approach doesn't appear to be compatible with recent EAL changes. For instance, the multi-process communication creates a couple handler threads ("rte_mp_handle" and "rte_mp_async") during EAL initialization. The child processes won't inherit these threads, and so won't be able to participate in multi-process comms. This means the reworked memory subsystem and upcoming device hotplug support (http://mails.dpdk.org/archives/dev/2018-July/107704.html) won't work with this fork-after-init model.

This is just one example - there may be other features/subsystems that won't work. As far as I can tell there is no official stance (though the l2fwd_fork example implies it's supported, IMO); I think either DPDK should either drop the example and not support this model, or support it and either document its limitations or resolve them. This model could be an interesting way to run multi-process DPDK on an ASLR-enabled system, but supporting this wouldn't be trivial.

Thanks,
Gage