[dpdk-dev] [RFC] Service Cores concept

[Bruce Richardson]

On Wed, May 17, 2017 at 12:11:10AM +0200, Thomas Monjalon wrote:
> 03/05/2017 13:29, Harry van Haaren:
> > The concept is to allow a software function register itself with EAL as
> > a "service", which requires CPU time to perform its duties. Multiple
> > services can be registered in an application, if more than one service
> > exists. The application can retrieve a list of services, and decide how
> > many "service cores" to use. The number of service cores is removed
> > from the application usage, and they are mapped to services based on
> > an application supplied coremask.
> > 
> > The application now continues as normal, without having to manually
> > schedule and implement arbitration of CPU time for the SW services.
> 
> I think it should not be the DPDK responsibility to schedule threads.
> The mainloops and scheduling are application design choices.
> 
> If I understand well the idea of your proposal, it is a helper for
> the application to configure the thread scheduling of known services.
> So I think we could add interrupt processing and other thread creations
> in this concept.
> Could we also embed the rte_eal_mp_remote_launch() calls in this concept?


There are a couple of parts of this:
1. Allowing libraries and drivers to register the fact that they require
background processing, e.g. as a SW fallback for functionality that
would otherwise be implemented in hardware
2. Providing support for easily multi-plexing these independent
functions from different libs onto a different core, compared to the
normal operation of DPDK of firing a single run-forever function on each
core.
3. Providing support for the application to configure the running of
these background services on specific cores.
4. Once configured, hiding these services and the cores they run on from
the rest of the application, so that the rest of the app logic does not
need to change depending on whether service cores are in use or not. For
instance, removing the service cores from the core list in foreach-lcore
loops, and preventing the EAL from trying to run app functions on the
cores when the app calls mp_remote_launch.

Overall, the objective is to provide us a way to have software
equivalents of hardware functions in as transparent a manner as
possible. There is a certain amount of scheduling being done by the
DPDK, but it is still very much under the control of the app.

As for other things being able to use this concept, definite +1 for
interrupt threads and similar. I would not see mp_remote_launch as being
affected here in any significant way (except from the hiding service
cores from it, obviously)

/Bruce