RE: [PATCH 4/6] service: tweak cycle statistics semantics

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

> -----Original Message-----
> From: Morten Brørup <mb@smartsharesystems.com>
> Sent: Wednesday, September 7, 2022 9:41 AM
> To: mattias.ronnblom <mattias.ronnblom@ericsson.com>; Van Haaren, Harry
> <harry.van.haaren@intel.com>
> Cc: dev@dpdk.org; Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>; nd
> <nd@arm.com>
> Subject: RE: [PATCH 4/6] service: tweak cycle statistics semantics
> 
> > From: Mattias Rönnblom [mailto:mattias.ronnblom@ericsson.com]
> > Sent: Tuesday, 6 September 2022 18.14
> >
> > As a part of its service function, a service usually polls some kind
> > of source (e.g., an RX queue, a ring, an eventdev port, or a timer
> > wheel) to retrieve one or more items of work.
> >
> > In low-load situations, the service framework reports a significant
> > amount of cycles spent for all running services, despite the fact they
> > have performed little or no actual work.
> >
> > The per-call cycle expenditure for an idle service (i.e., a service
> > currently without pending jobs) is typically very low. Polling an
> > empty ring or RX queue is inexpensive. However, since the service
> > function call frequency on an idle or lightly loaded lcore is going to
> > be very high indeed, the service function calls' cycles adds up to a
> > significant amount. The only thing preventing the idle services'
> > cycles counters to make up 100% of the available CPU cycles is the
> > overhead of the service framework itself.
> >
> > If the RTE_SERVICE_ATTR_CYCLES or RTE_SERVICE_LCORE_ATTR_CYCLES are
> > used to estimate service core load, the cores may look very busy when
> > the system is mostly doing nothing useful at all.
> >
> > This patch allows for an idle service to indicate that no actual work
> > was performed during a particular service function call (by returning
> > -EAGAIN). In such cases the RTE_SERVICE_ATTR_CYCLES and
> > RTE_SERVICE_LCORE_ATTR_CYCLES values are not incremented.
> >
> > The convention of returning -EAGAIN for idle services may in the
> > future also be used to have the lcore enter a short sleep, or reduce
> > its operating frequency, in case all services are currently idle.
> >
> > This change is backward-compatible.
> >
> > Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> > ---
> 
> This entire series contains a bunch of good improvements.
> 
> Returning -EAGAIN is a step in the right direction towards measuring CPU usage, and
> a great way to make it backwards compatible.
> 
> Series-Acked-by: Morten Brørup <mb@smartsharesystems.com>

Agreed, thanks Mattias for authoring & Morten for review/ack;

I've left 2 minor comments on individual patches, but for the remaining 4 patches;
Series-Acked-by: Harry van Haaren <harry.van.haaren@intel.com>