Re: [dpdk-dev] [PATCH v2 1/2] service: add component useful work attribute

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

> -----Original Message-----
> From: David Marchand <david.marchand@redhat.com>
> Sent: Friday, October 16, 2020 1:20 PM
> To: Van Haaren, Harry <harry.van.haaren@intel.com>; Mattias Rönnblom
> <mattias.ronnblom@ericsson.com>
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2 1/2] service: add component useful work
> attribute
> 
> On Mon, Oct 5, 2020 at 8:59 PM Van Haaren, Harry
> <harry.van.haaren@intel.com> wrote:
> > > -----Original Message-----
> > > From: dev <dev-bounces@dpdk.org> On Behalf Of Van Haaren, Harry
> > > Sent: Wednesday, September 23, 2020 3:17 PM
> > > To: Mattias Rönnblom <mattias.ronnblom@ericsson.com>; dev@dpdk.org
> > > Cc: david.marchand@dpdk.org
> > > Subject: Re: [dpdk-dev] [PATCH v2 1/2] service: add component useful work
> > > attribute
> > >
> > > > -----Original Message-----
> > > > From: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> > > > Sent: Wednesday, September 23, 2020 12:40 PM
> > > > To: Van Haaren, Harry <harry.van.haaren@intel.com>; dev@dpdk.org
> > > > Cc: david.marchand@dpdk.org
> > > > Subject: Re: [dpdk-dev] [PATCH v2 1/2] service: add component useful
> work
> > > > attribute
> > >
> > > Hi Mattias,
> > >
> > > Thanks for taking time to review & prompt reply!
> >
> > Ping Mattias - any input based on follow up discussion below?
> >
> >
> > > > On 2020-09-14 16:37, Harry van Haaren wrote:
> > > > > This commit adds a new attribute which allows the service to indicate
> > > > > if the previous iteration of work was "useful". Useful work here implies
> > > > > forward progress was made.
> > > >
> > > > > Exposing this information via an attribute to the application allows
> > > > > tracking of CPU cycles as being useful or not-useful, and a CPU load
> > > > > estimate can be deduced from that information.
> > > >
> > > >
> > > > How would that tracking be implemented? rte_service.c already keeps
> > > > track of the amount of busy cycles per service. Would it be possible to
> > > > reuse that mechanism to achieve the same goal?
> > >
> > > Tracking "busy cycles" is not exactly the same - Eventdev SW PMD can spend
> > > cycles polling, and trying to move packets around its internal queues, but
> make
> > > no forward progress. Measuring cycles spent in the service would not indicate
> > > the correct "busyness" in that case.
> > >
> > > In the suggested patchset, each service (e.g Eventdev SW PMD) can update
> > > a statistic itself, pushing an attribute value into the service-cores layer.
> > > This method allows each PMD to define "useful work" in its own way.
> > >
> > > > We did some prototyping on dynamic load balancing for the service core
> > > > framework, and then we extended the API is such a way that the service
> > > > callback would return a bool indicating if forward progress was made, if
> > > > I recall correctly. Sampling these counters allowed for tracking load on
> > > > both a per-lcore and per-service basis.
> > >
> > > The service callback return value can be stored/inspected on the service-core
> > > itself, but how to show that to the application? It still requires an attribute API
> > > like proposed below re-using "attr_get" API I think.
> > >
> > > So really the only difference in the prototype you mention is how the
> > > service itself communicates business to the service-cores infrastructure in
> EAL.
> > >
> > > Perhaps re-purposing return-value is simpler, but it limits statistics from the
> > > service to just business, and the API change requires all services to change.
> > >
> > > Pros of adding an API as this patchset proposes is to push attribute values to
> > > service-core in EAL is extensibility, and no API breakage.
> > >
> > > Given that context, Ack / push-back to this suggested approach?
> 
> I need a conclusion.
> Is this required for 20.11?

Given timeline - lets leave this until 21.02 release.
I think the above solution is adequate, but don't want to rush folks.

Thanks for following up, chat next release. -Harry