On Fri, Aug 26, 2022 at 1:37 PM Bruce Richardson
<bruce.richard...@intel.com> wrote:
>
> On Fri, Aug 26, 2022 at 12:35:16PM +0530, Jerin Jacob wrote:
> > On Thu, Aug 25, 2022 at 8:56 PM Kevin Laatz <kevin.la...@intel.com> wrote:
> > >
> > > From: Anatoly Burakov <anatoly.bura...@intel.com>
> > >
> > > Currently, there is no way to measure lcore poll busyness in a passive
> > > way,
> > > without any modifications to the application. This patch adds a new EAL
> > > API
> > > that will be able to passively track core polling busyness.
> > >
> > > The poll busyness is calculated by relying on the fact that most DPDK
> > > API's
> > > will poll for packets. Empty polls can be counted as "idle", while
> > > non-empty polls can be counted as busy. To measure lcore poll busyness, we
> > > simply call the telemetry timestamping function with the number of polls a
> > > particular code section has processed, and count the number of cycles
> > > we've
> > > spent processing empty bursts. The more empty bursts we encounter, the
> > > less
> > > cycles we spend in "busy" state, and the less core poll busyness will be
> > > reported.
> > >
> > > In order for all of the above to work without modifications to the
> > > application, the library code needs to be instrumented with calls to the
> > > lcore telemetry busyness timestamping function. The following parts of
> > > DPDK
> > > are instrumented with lcore telemetry calls:
> > >
> > > - All major driver API's:
> > > - ethdev
> > > - cryptodev
> > > - compressdev
> > > - regexdev
> > > - bbdev
> > > - rawdev
> > > - eventdev
> > > - dmadev
> > > - Some additional libraries:
> > > - ring
> > > - distributor
> > >
> > > To avoid performance impact from having lcore telemetry support, a global
> > > variable is exported by EAL, and a call to timestamping function is
> > > wrapped
> > > into a macro, so that whenever telemetry is disabled, it only takes one
> > > additional branch and no function calls are performed. It is also possible
> > > to disable it at compile time by commenting out RTE_LCORE_BUSYNESS from
> > > build config.
> > >
> > > This patch also adds a telemetry endpoint to report lcore poll busyness,
> > > as
> > > well as telemetry endpoints to enable/disable lcore telemetry. A
> > > documentation entry has been added to the howto guides to explain the
> > > usage
> > > of the new telemetry endpoints and API.
> > >
> > > Signed-off-by: Kevin Laatz <kevin.la...@intel.com>
> > > Signed-off-by: Conor Walsh <conor.wa...@intel.com>
> > > Signed-off-by: David Hunt <david.h...@intel.com>
> > > Signed-off-by: Anatoly Burakov <anatoly.bura...@intel.com>
> > >
> > > ---
> > > v3:
> > > * Fix missed renaming to poll busyness
> > > * Fix clang compilation
> > > * Fix arm compilation
> > >
> > > v2:
> > > * Use rte_get_tsc_hz() to adjust the telemetry period
> > > * Rename to reflect polling busyness vs general busyness
> > > * Fix segfault when calling telemetry timestamp from an unregistered
> > > non-EAL thread.
> > > * Minor cleanup
> > > ---
> >
> > > diff --git a/meson_options.txt b/meson_options.txt
> > > index 7c220ad68d..725b851f69 100644
> > > --- a/meson_options.txt
> > > +++ b/meson_options.txt
> > > @@ -20,6 +20,8 @@ option('enable_driver_sdk', type: 'boolean', value:
> > > false, description:
> > > 'Install headers to build drivers.')
> > > option('enable_kmods', type: 'boolean', value: false, description:
> > > 'build kernel modules')
> > > +option('enable_lcore_poll_busyness', type: 'boolean', value: true,
> > > description:
> > > + 'enable collection of lcore poll busyness telemetry')
> >
> > IMO, All fastpath features should be opt-in. i.e default should be false.
> > For the trace fastpath related changes, We have done the similar thing
> > even though it cost additional one cycle for disabled trace points
> >
>
> We do need to consider runtime and build defaults differently, though.
> Since this has also runtime enabling, I think having build-time enabling
> true as default is ok, so long as the runtime enabling is false (assuming
> no noticable overhead when the feature is disabled.)
I was talking about buildtime only. "enable_trace_fp" meson option selected as
false as default.
If the concern is enabling on generic distros then distro generic
config can opt in this
>
> /Bruce
