RE: [PATCH v3 1/3] eal: add lcore poll busyness telemetry

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Kevin Laatz [mailto:kevin.laatz@intel.com]
> Sent: Monday, 29 August 2022 15.37
> 
> On 29/08/2022 13:49, Morten Brørup wrote:
> > From: Kevin Laatz [mailto:kevin.laatz@intel.com]
> > Sent: Monday, 29 August 2022 14.37
> >> The patches currently include runtime options to enable/disable the
> feature via API and via telemetry endpoints. We have run performance
> tests and have failed to measure any performance impact with the
> feature runtime disabled.
> > Lots of features are added to DPDK all the time, and they all use the
> same "insignificant performance impact" argument. But the fact is, each
> added test-and-branch has some small performance impact (and consume
> some entries in the branch prediction table, which may impact
> performance elsewhere). If you add a million features using this
> argument, there will be a significant and measurable performance
> impact.
> >
> > Which is why I keep insisting on the ability to omit non-core
> features from DPDK at build time.
> 
> I think there's general consensus in having a buildtime option to
> disable it.
> 
> Do we agree that it should be buildtime enabled, and runtime disabled
> by
> default (so just the single additional branch by default), with the
> meson option available to disable it completely at buildtime?

No. This feature is in the fast path, so please follow the "enable_trace_fp" design pattern, which also has fast path trace disabled at build time.

-Morten