Re: [dpdk-dev] [RFCv2] service core concept

[Jerin Jacob <jerin.jacob@caviumnetworks.com>]

-----Original Message-----
> Date: Fri, 2 Jun 2017 16:09:13 +0000
> From: "Van Haaren, Harry" <harry.van.haaren@intel.com>
> To: "dev@dpdk.org" <dev@dpdk.org>
> CC: Thomas Monjalon <thomas@monjalon.net>, Jerin Jacob
>  <jerin.jacob@caviumnetworks.com>, "Richardson, Bruce"
>  <bruce.richardson@intel.com>, "Ananyev, Konstantin"
>  <konstantin.ananyev@intel.com>, "Wiles, Keith" <keith.wiles@intel.com>
> Subject: [dpdk-dev] [RFCv2] service core concept
> 
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Van Haaren, Harry
> > Sent: Thursday, May 25, 2017 2:28 PM
> > Subject: Re: [dpdk-dev] [RFC] service core concept header implementation
> > 
> > Thanks everybody for the input on the RFC - appreciated! From an application point-of-view, I
> > see merit in Konstantin's suggestions for the API, over the RFC I sent previously. I will re-
> > work the API taking inspiration from both APIs and send an RFCv2, you'll be on CC :)
> 
> 
> Hi All,
> 
> This email is the v2 RFC for Service Cores, in response to the v1 sent previously[1].
> The service-cores API has been updated, and various concepts have changed.
> 
> The API has been redesigned, with Konstantin's API suggestions as a base, and the
> other comments taken into account. In my opinion this v2 API is more application-centric,
> and enables the common application tasks much better. Such tasks are for example start/stop
> of a service, and add/remove of a service core.
> 
> In particular this version of the API enables applications that are not aware of services to
> benefit from the services concept, as EAL args can be used to setup services and service cores.
> With this design, switching to/from SW/HW PMD is transparent to the application. An example
> use-case is the Eventdev HW PMD to Eventdev SW PMD that requires a service core. 
> 
> I have noted the implementation comments that were raised on the v1. For v2, I think our time
> is better spent looking at the API design, and I will handle implementation feedback in the
> follow-up patchset to v2 RFC.
> 
> Below a summary of what we are trying to achieve, and the current API design.
> Have a good weekend! Cheers, -Harry
> 
> 
> Summary of goals (summarized from a previous email)
> 1. Allowing libraries and drivers to register the fact that they require background processing
> 2. Providing support for easily multiplexing these independent functions from different libs onto a different 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
> 
> 
> === RFC v2 API ===
> 
> There are 3 parts to the API; they separate the concerns of each "user" of the API:
> 	- Service Registration
> 	- Service Config
> 	- ServiceCore Config
> 
> Service Registration: 
> A service requires a core. It only knows about its NUMA node, and that it requires CPU time.
> Registration of a service requires only that information.
> 
> Service Config:
> An application may configure what service runs where using the Service Config APIs.
> EAL is capable of performing this during rte_eal_init() if requested by passing a
> --service-cores argument. The application (mostly) calls these functions at initialization
> time, with start() and stop() being available to dynamically switch on/off a service if required.
> 
> ServiceCore Config
> An application can start/stop or add/remove service-lcores using the ServiceCore Config, allowing
> dynamically scaling the number of used lcores by services. Lcores used as service-cores are removed
> from the application coremask, and are not available to remote_launch() as they are already in use.
> 
> 
> Service Registration:
> int32_t rte_service_register(const struct rte_service_spec *spec);
> int32_t rte_service_unregister(struct rte_service_spec *service);
> 
> Service Configuration:
> uint32_t rte_service_get_count(void);
> struct rte_service_spec *rte_service_get_by_id(uint32_t id);
> const char *rte_service_get_name(const struct rte_service_spec *service);
> int32_t rte_service_set_coremask(struct rte_service_spec *service, const rte_cpuset_t *coremask);
> int32_t rte_service_start(struct rte_service_spec *service); /* runtime function */
> int32_t rte_service_stop(struct rte_service_spec *service);  /* runtime function */

Looks good to me in general.

How about an API to query the service function running status?
bool rte_service_is_running(struct rte_service_spec *service); or something similar.


> 
> ServiceCore Configuration:
> int32_t rte_service_cores_start(void);
> int32_t rte_service_cores_stop(void);
> int32_t rte_service_cores_add(const rte_cpuset_t *coremask);
> int32_t rte_service_cores_del(const rte_cpuset_t *coremask);
> 
> 
> I am working on a patchset - but for now I would appreciate general design feedback,
> particularly if a specific use-case is not handled.