Re: [PATCH] eal: added new `rte_lcore_is_service_lcore` API.

[Pavan Nikhilesh Bhagavatula <pbhagavatula@caviumnetworks.com>]

On Mon, Aug 28, 2017 at 03:24:06PM +0000, Van Haaren, Harry wrote:
>
>
> > -----Original Message-----
> > From: Pavan Nikhilesh Bhagavatula [mailto:pbhagavatula@caviumnetworks.com]
> > Sent: Monday, August 28, 2017 4:10 PM
> > To: Van Haaren, Harry <harry.van.haaren@intel.com>
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH] eal: added new `rte_lcore_is_service_lcore` API.
> >
> > On Mon, Aug 28, 2017 at 01:49:37PM +0000, Van Haaren, Harry wrote:
> > > > From: Pavan Nikhilesh Bhagavatula [mailto:pbhagavatula@caviumnetworks.com]
> > > > Sent: Monday, August 28, 2017 12:33 PM
> > > > To: Van Haaren, Harry <harry.van.haaren@intel.com>
> > > > Cc: dev@dpdk.org
> > > > Subject: Re: [dpdk-dev] [PATCH] eal: added new `rte_lcore_is_service_lcore` API.
> > > >
> > > > On Mon, Aug 28, 2017 at 10:59:51AM +0000, Van Haaren, Harry wrote:
> > > > > > From: Pavan Nikhilesh [mailto:pbhagavatula@caviumnetworks.com]
> > > > > > Sent: Wednesday, August 23, 2017 4:10 PM
> > > > > > To: dev@dpdk.org
> > > > > > Cc: Van Haaren, Harry <harry.van.haaren@intel.com>; Pavan Nikhilesh
> > > > > > <pbhagavatula@caviumnetworks.com>
> > > > > > Subject: [dpdk-dev] [PATCH] eal: added new `rte_lcore_is_service_lcore` API.
> > > > > >
> > > > > > This API can be used to test if an lcore(EAL thread) is a service lcore.
> > > > > >
> > > > > > Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
> > > > > > ---
> > > > > >  lib/librte_eal/common/include/rte_lcore.h | 18 ++++++++++++++++++
> > > > > >  1 file changed, 18 insertions(+)
> > > > > >
> > > > > > diff --git a/lib/librte_eal/common/include/rte_lcore.h
> > > > > > b/lib/librte_eal/common/include/rte_lcore.h
> > > > > > index 50e0d0f..7854ea1 100644
> > > > > > --- a/lib/librte_eal/common/include/rte_lcore.h
> > > > > > +++ b/lib/librte_eal/common/include/rte_lcore.h
> > > > > > @@ -180,6 +180,24 @@ rte_lcore_is_enabled(unsigned lcore_id)
> > > > > >  }
> > > > > >
> > > > > >  /**
> > > > > > + * Test if an lcore is service lcore.
> > > > > > + *
> > > > > > + * @param lcore_id
> > > > > > + *   The identifier of the lcore, which MUST be between 0 and
> > > > > > + *   RTE_MAX_LCORE-1.
> > > > > > + * @return
> > > > > > + *   True if the given lcore is service; false otherwise.
> > > > > > + */
> > > > > > +static inline int
> > > > > > +rte_lcore_is_service_lcore(unsigned lcore_id)
> > > > > > +{
> > > > > > +	struct rte_config *cfg = rte_eal_get_configuration();
> > > > > > +	if (lcore_id >= RTE_MAX_LCORE)
> > > > > > +		return 0;
> > > > > > +	return cfg->lcore_role[lcore_id] == ROLE_SERVICE;
> > > > > > +}
> > > > >
> > > > > No header file and Static inline - so this is only to be used internally in the service
> > > > cores library?
> > > > > If so, the function should actually be used, instead of only added but not used in the
> > > > library itself.
> > > > >
> > > >
> > > > The enum rte_lcore_role_t has ROLE_SERVICE which tells that a particular lcore is
> > > > a service lcore as well as an EAL thread some libraries such as rte_timer allow
> > > > specific operations only over EAL threads.
> > >
> > > Understood that role of cores is important, and that rte_timer might require this
> > information.
> > >
> > >
> > > > The rte_timer lib uses the rte_is_lcore_enabled() call to check if a lcore is an
> > > > EAL thread, Which checks if the lcore role is  ROLE_RTE. But it should also
> > > > allow timers to be registered on a service core as processing those timers can
> > > > be done on them.
> > >
> > > No problem from me here either - although it's the Timers library maintainer that should
> > check this.
> > >
> > >
> > > > This new function allows such libraries to check if the role is
> > > > ROLE_SERVICE and allow those operations.
> > >
> > > If the timers library requires information about service-cores, it should use a public API
> > to retrieve that information. Having "internal" functions between libraries is not nice.
> > >
> > > I think a better design would be to add this function as a public function, (add it to the
> > .map files etc) and then call the public function from the timers library.
> > >
> > > Does that sound like a good solution? -Harry
> > >
> >
> > The file rte_lcore.h is in librte_eal/common/include I couldn't find a .map
> > file for eal/common and also other functions that are present in rte_lcore.h
> > aren't mapped in eal/linuxapp or eal/bsdapp.
> > I think it is fine as the functions are static inline.
> >
> > -Pavan
>
> OK - I was looking at this from a service core library POV. The intent seems to be to update EAL in order to allow detection of a core having a ROLE_SERVICE. Now I see your intent better, no problem with the approach. Correct that static-inline functions don't need .map file entries (cause they're inlined :)
>
> One technical issue:
> > +	if (lcore_id >= RTE_MAX_LCORE)
> > +		return 0;
>
> This should return a -ERROR value, as 0 is a valid return value that should indicate one thing (and one thing only) "not a service core".

The function function follows the same structure as rte_lcore_is_enabled i.e.
returns either true(1) or false(0). So, I think returning 0 would be fine?. If
not I'll gladly send a v2.

Thanks for the inputs :). -Pavan.
>
> Please spin a v2 and I'll Ack.
>
> >
> > >
> > > > Currently, the only rte_timer library has this specific role check. The
> > > > following patch shows the usage in rte_timer library.
> > > >
> > > > http://dpdk.org/dev/patchwork/patch/27819/
> > > >
> > > > > Or am I mis-understanding the intent?
> > > > >
> > > > > -Harry
> > > >
> > > > Thanks,
> > > > Pavan.