Re: Service lcores and Application lcores

["Van Haaren, Harry" <harry.van.haaren@intel.com>]

> From: Jerin Jacob [mailto:jerin.jacob@caviumnetworks.com]
> Sent: Friday, June 30, 2017 1:52 PM
> To: Van Haaren, Harry <harry.van.haaren@intel.com>
> Cc: Richardson, Bruce <bruce.richardson@intel.com>; dev@dpdk.org; thomas@monjalon.net;
> Wiles, Keith <keith.wiles@intel.com>
> Subject: Re: Service lcores and Application lcores
> 
> -----Original Message-----
> > Date: Fri, 30 Jun 2017 10:00:18 +0000
> > From: "Van Haaren, Harry" <harry.van.haaren@intel.com>
> > To: Jerin Jacob <jerin.jacob@caviumnetworks.com>, "Richardson, Bruce"
> >  <bruce.richardson@intel.com>
> > CC: "dev@dpdk.org" <dev@dpdk.org>, "thomas@monjalon.net"
> >  <thomas@monjalon.net>, "Wiles, Keith" <keith.wiles@intel.com>
> > Subject: RE: Service lcores and Application lcores

<snip previous non-related items>

> > I don't think providing a remote-launch API is actually beneficial. Remote-launching a
> single service
> > is equivalent to adding that lcore as a service-core, and mapping it to just that single
> service.
> > The advantage of adding it as a service core, is future-proofing for if more services
> need to be added
> > to that core in future, and statistics of the service core infrastructure. A convenience
> API could be
> > provided to perform the core_add(), service_start(), enable_on_service() and
> core_start() APIs in one.
> >
> > Also, the remote_launch API doesn't solve the original problem - what if an application
> lcore wishes
> > to run one iteration of a service "manually". The remote_launch style API does not solve
> this problem.
> 
> Agree with problem statement. But, remote_launch() operates on lcores not on
> not necessary on 1:1 mapped physical cores.
> 
> By introducing "rte_service_iterate", We are creating a parallel infrastructure to
> run the service on non DPDK service lcores aka normal lcores.
> Is this really required? Is there  any real advantage for
> application not use builtin service lcore infrastructure, rather than iterating over
> "rte_service_iterate" and run on normal lcores. If we really want to mux
> a physical core to N lcore, EAL already provides that in the form of threads.
> 
> I think, providing too many parallel options for the same use case may be
> a overkill.
> 
> Just my 2c.


The use-case that the rte_service_iterate() caters for is one where the application
wishes to run a service on an "ordinary app lcore", together with an application workload.

For example, the eventdev-scheduler and one worker can be run on the same lcore. If the schedule() running thread *must* be a service lcore, we would not be able to also use that lcore as an application worker core.

That was my motivation for adding this API, I do agree with you above; it is a second "parallel" method to run a service. I think there's enough value in enabling the use-case as per example above to add it.


Do you see enough value in the use-case above to add the API?