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From: "Van Haaren, Harry" <harry.van.haaren@intel.com>
Subject: Re: Service lcores and Application lcores
Date: Fri, 30 Jun 2017 13:24:17 +0000
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Cc: "Richardson, Bruce" <bruce.richardson@intel.com>, "dev@dpdk.org"
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To: Jerin Jacob <jerin.jacob@caviumnetworks.com>
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> From: Jerin Jacob [mailto:jerin.jacob@caviumnetworks.com]
> Sent: Friday, June 30, 2017 2:21 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
>=20
> -----Original Message-----
> > Date: Fri, 30 Jun 2017 13:08:26 +0000
> > From: "Van Haaren, Harry" <harry.van.haaren@intel.com>
> > To: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> > CC: "Richardson, Bruce" <bruce.richardson@intel.com>, "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
> >
> > > 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; tho=
mas@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, Bruc=
e"
> > > >  <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 i=
t to just that
> single
> > > service.
> > > > The advantage of adding it as a service core, is future-proofing fo=
r if more
> services
> > > need to be added
> > > > to that core in future, and statistics of the service core infrastr=
ucture. A
> convenience
> > > API could be
> > > > provided to perform the core_add(), service_start(), enable_on_serv=
ice() and
> > > core_start() APIs in one.
> > > >
> > > > Also, the remote_launch API doesn't solve the original problem - wh=
at if an
> application
> > > lcore wishes
> > > > to run one iteration of a service "manually". The remote_launch sty=
le 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 infr=
astructure 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 ma=
y 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 ap=
plication
> workload.
> >
> > For example, the eventdev-scheduler and one worker can be run on the sa=
me 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 enabl=
ing the use-case
> as per example above to add it.
> >
> >
> > Do you see enough value in the use-case above to add the API?
>=20
> The above use case can be realized like --lcores=3D'(0-1)@1'(Two lcore on
> an physical core). I believe, application writers never want to write a
> code based on specific number of cores available in the system. If they
> do then they will be stuck on running on another environment and too
> many combination to address.

Good point.

> For me it complicates service lcore usage. But someone think, it will use=
ful then
> I don't have strong objection.

We can easily add APIs later - and removing them isn't so easy. +1 from me =
leave it out for now, and we can see about adding it for 17.11 if the need =
arises.

Thanks for your input, I'll spin a v3 without the rte_service_iterate() fun=
ction, and that should be it then!
=20