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

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

> From: Jerin Jacob [mailto:jerinjacobk@gmail.com]
> Sent: Wednesday, 18 September 2024 11.50
to omit trace
> 
> On Wed, Sep 18, 2024 at 2:39 PM Morten Brørup <mb@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@smartsharesystems.com>
> > ---
> >  app/test/test_trace.c                      | 11 ++++++++++-
> >  config/rte_config.h                        |  1 +
> >  lib/eal/include/rte_trace_point.h          |  6 +++++-
> >  lib/eal/include/rte_trace_point_register.h |  8 ++++++++
> >  4 files changed, 24 insertions(+), 2 deletions(-)
> >
> > diff --git a/app/test/test_trace.c b/app/test/test_trace.c
> > index 00809f433b..7918cc865d 100644
> > --- a/app/test/test_trace.c
> > +++ b/app/test/test_trace.c
> > @@ -12,7 +12,16 @@
> >
> >  int app_dpdk_test_tp_count;
> >
> > -#ifdef RTE_EXEC_ENV_WINDOWS
> > +#if !defined(RTE_TRACE)
> > +
> > +static int
> > +test_trace(void)
> > +{
> > +       printf("trace omitted at build-time, skipping test\n");
> > +       return TEST_SKIPPED;
> > +}
> > +
> > +#elif defined(RTE_EXEC_ENV_WINDOWS)
> >
> >  static int
> >  test_trace(void)
> > 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/include/rte_trace_point.h
> b/lib/eal/include/rte_trace_point.h
> > index 41e2a7f99e..1b60bba043 100644
> > --- a/lib/eal/include/rte_trace_point.h
> > +++ b/lib/eal/include/rte_trace_point.h
> > @@ -212,6 +212,7 @@ bool rte_trace_point_is_enabled(rte_trace_point_t *tp);
> >  __rte_experimental
> >  rte_trace_point_t *rte_trace_point_lookup(const char *name);
> >
> > +#ifdef RTE_TRACE
> >  /**
> >   * @internal
> >   *
> > @@ -230,6 +231,7 @@ __rte_trace_point_fp_is_enabled(void)
> >         return false;
> >  #endif
> >  }
> > +#endif /* RTE_TRACE */
> >
> >  /**
> >   * @internal
> > @@ -356,6 +358,8 @@ __rte_trace_point_emit_ev_header(void *mem, uint64_t in)
> >         return RTE_PTR_ADD(mem, __RTE_TRACE_EVENT_HEADER_SZ);
> >  }
> >
> > +#ifdef RTE_TRACE
> 
> 
> Please change to 1.4.5 style _if possible_ in
> https://doc.dpdk.org/guides/contributing/coding_style.html.

The Coding Style's chapter 1.4.5 only applies to O/S selection.
Boolean configuration definitions either have the value 1 or are not defined.

> Assuming linker will remove the memory from the image if it is not
> using by stubbing out.

Assumption could be false if building with optimizations disabled. Don't know.

> 
> Untested.
> 
> #define __rte_trace_point_emit_header_generic(t) \
> void *mem; \
> do { \
>   +      if (RTE_TRACE_ENABLED == 0) \
>   +             return \
>         const uint64_t val = rte_atomic_load_explicit(t,
> rte_memory_order_acquire); \
>         if (likely(!(val & __RTE_TRACE_FIELD_ENABLE_MASK))) \
>                 return; \
>         mem = __rte_trace_mem_get(val); \
>         if (unlikely(mem == NULL)) \
>                 return; \
>         mem = __rte_trace_point_emit_ev_header(mem, val); \
> } while (0)

I was initially down that path, inspired by how FP is enabled/disabled;
using an added __rte_trace_point_is_enabled(void) inline function, like the __rte_trace_point_fp_is_enabled(void).

But I kept getting lots of warnings, either about nonexisting references, or stuff not being used.

So I gave up and did it this way instead.
After having tried the other way, this way also looks cleaner to me.

> 
> 
> 
> > +
> >  #define __rte_trace_point_emit_header_generic(t) \
> >  void *mem; \
> >  do { \
> > @@ -411,7 +415,7 @@ do { \
> >         RTE_SET_USED(len); \
> >  } while (0)
> >
> > -
> > +#endif /* RTE_TRACE */
> >  #endif /* ALLOW_EXPERIMENTAL_API */
> >  #endif /* _RTE_TRACE_POINT_REGISTER_H_ */
> >
> > diff --git a/lib/eal/include/rte_trace_point_register.h
> b/lib/eal/include/rte_trace_point_register.h
> > index 41260e5964..78c0ede5f1 100644
> > --- a/lib/eal/include/rte_trace_point_register.h
> > +++ b/lib/eal/include/rte_trace_point_register.h
> > @@ -18,6 +18,8 @@ extern "C" {
> >
> >  RTE_DECLARE_PER_LCORE(volatile int, trace_point_sz);
> >
> > +#ifdef RTE_TRACE
> > +
> >  #define RTE_TRACE_POINT_REGISTER(trace, name) \
> >  rte_trace_point_t __rte_section("__rte_trace_point") __##trace; \
> >  static const char __##trace##_name[] = RTE_STR(name); \
> > @@ -27,6 +29,12 @@ RTE_INIT(trace##_init) \
> >                 (void (*)(void)) trace); \
> >  }
> >
> > +#else
> > +
> > +#define RTE_TRACE_POINT_REGISTER(trace, name)
> > +
> > +#endif /* RTE_TRACE */
> > +
> >  #define __rte_trace_point_emit_header_generic(t) \
> >         RTE_PER_LCORE(trace_point_sz) = __RTE_TRACE_EVENT_HEADER_SZ
> >
> > --
> > 2.43.0
> >