[PATCH v6] eal: add build-time option to omit trace

[Morten Brørup]

> From: Jerin Jacob [mailto:jerinjacobk at gmail.com]
> Sent: Monday, 7 October 2024 07.45
> 
> On Sun, Oct 6, 2024 at 7:44 PM Morten Brørup <mb at smartsharesystems.com>
> wrote:
> >
> > Some applications want to omit the trace feature.
> > Either to reduce the memory footprint, to reduce the exposed attack
> > surface, or for other reasons.
> >
> > This patch adds an option in rte_config.h to include or omit trace in
> the
> > build. Trace is included by default.
> >
> > Omitting trace works by omitting all trace points.
> > For API and ABI compatibility, the trace feature itself remains.
> >
> > Signed-off-by: Morten Brørup <mb at smartsharesystems.com>
> > ---
> > v6:
> >   Removed test_trace_perf.c changes; they don't compile for Windows
> >   target, and are superfluous.
> > v5:
> >   Added public function rte_trace_feature_is_enabled(), to test if
> trace
> >   is build time enabled in both the DPDK and the application. Use in
> test
> >   application instead of private function. (Jerin Jacob)
> > v4:
> > * Added check for generic trace enabled when registering trace
> points, in
> >   RTE_INIT. (Jerin Jacob)
> > * Test application uses function instead of macro to check if generic
> >   trace is enabled. (Jerin Jacob)
> > * Performance test application uses function to check if generic
> trace is
> >   enabled.
> > v3:
> > * Simpler version with much fewer ifdefs. (Jerin Jacob)
> > v2:
> > * Added/modified macros required for building applications with trace
> >   omitted.
> > ---
> >  app/test/test_trace.c                      |  4 +++
> >  config/rte_config.h                        |  1 +
> >  lib/eal/common/eal_common_trace.c          | 10 +++++++
> >  lib/eal/include/rte_trace.h                | 33
> ++++++++++++++++++++++
> >  lib/eal/include/rte_trace_point.h          | 21 ++++++++++++++
> >  lib/eal/include/rte_trace_point_register.h |  2 ++
> >  lib/eal/version.map                        |  3 ++
> >  7 files changed, 74 insertions(+)
> >
> > diff --git a/app/test/test_trace.c b/app/test/test_trace.c
> > index 00809f433b..8ea1443044 100644
> > --- a/app/test/test_trace.c
> > +++ b/app/test/test_trace.c
> > @@ -245,6 +245,10 @@ static struct unit_test_suite trace_tests = {
> >  static int
> >  test_trace(void)
> >  {
> > +       if (!rte_trace_feature_is_enabled()) {
> > +               printf("Trace omitted at build-time, skipping
> test\n");
> > +               return TEST_SKIPPED;
> > +       }
> >         return unit_test_suite_runner(&trace_tests);
> >  }
> >
> > diff --git a/config/rte_config.h b/config/rte_config.h
> > index dd7bb0d35b..fd6f8a2f1a 100644
> > --- a/config/rte_config.h
> > +++ b/config/rte_config.h
> > @@ -49,6 +49,7 @@
> >  #define RTE_MAX_TAILQ 32
> >  #define RTE_LOG_DP_LEVEL RTE_LOG_INFO
> >  #define RTE_MAX_VFIO_CONTAINERS 64
> > +#define RTE_TRACE 1
> >
> >  /* bsd module defines */
> >  #define RTE_CONTIGMEM_MAX_NUM_BUFS 64
> > diff --git a/lib/eal/common/eal_common_trace.c
> b/lib/eal/common/eal_common_trace.c
> > index 918f49bf4f..06130c756d 100644
> > --- a/lib/eal/common/eal_common_trace.c
> > +++ b/lib/eal/common/eal_common_trace.c
> > @@ -100,6 +100,16 @@ rte_trace_is_enabled(void)
> >         return rte_atomic_load_explicit(&trace.status,
> rte_memory_order_acquire) != 0;
> >  }
> >
> > +bool
> > +__rte_trace_feature_is_enabled(void)
> > +{
> > +#ifdef RTE_TRACE
> > +       return true;
> > +#else
> > +       return false;
> > +#endif
> > +}
> > +static __rte_always_inline
> > +bool rte_trace_feature_is_enabled(void)
> > +{
> > +#ifdef RTE_TRACE
> > +       return __rte_trace_feature_is_enabled();
> > +#else
> > +       return false;
> > +#endif
> > +}
> > +__rte_experimental
> > +static __rte_always_inline bool
> > +__rte_trace_point_generic_is_enabled(void)
> > +{
> > +#ifdef RTE_TRACE
> > +       return true;
> > +#else
> > +       return false;
> > +#endif
> 
> __rte_trace_feature_is_enabled(), rte_trace_feature_is_enabled(),
> __rte_trace_point_generic_is_enabled() are duplicates.
> There is no harm in using a public API inside the implementation.
> Please keep only rte_trace_feature_is_enabled()
> and use it across implementation and app/test.

They are there to support DPDK being built as a library, and the application being built separately with a different rte_config.h.
But I suppose we generally don't support that. I will spin another version, which assumes that both DPDK (library) and application are built with the same rte_config.h.

I will rename __rte_trace_point_generic_is_enabled() to rte_trace_feature_is_enabled(), make it non-internal, and use that everywhere. It still needs to be inline, so the compiler can recognize it and omit the implementation when building with RTE_TRACE disabled.

> 
> > +}
> > +
> >  /**
> >   * @internal
> >   *
> 
> >         rte_vfio_get_device_info; # WINDOWS_NO_EXPORT
> > +
> > +       # added in 24.11
> > +       __rte_trace_feature_is_enabled;
> 
> rte_trace_feature_is_enabled;

It will be inline, and thus removed from here.

> 
> With the above changes,
> 
> Acked-by: Jerin Jacob <jerinj at marvell.com>

Thank you for the quick response, Jerin.