Re: [PATCH v2] eal: add build-time option to omit trace

[Jerin Jacob <jerinjacobk@gmail.com>]

On Thu, Sep 19, 2024 at 1:37 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>
> ---
> v2:
> * Added/modified macros required for building applications with trace
>   omitted.
> ---
>  app/test/test_trace.c                      | 11 ++++++++++-
>  config/rte_config.h                        |  1 +
>  lib/eal/include/rte_trace_point.h          | 22 +++++++++++++++++++++-
>  lib/eal/include/rte_trace_point_register.h | 17 +++++++++++++++++
>  4 files changed, 49 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


Too many ifdefs down using this, IMO, This approach will make
difficult to manage the code and make sure
 RTE_TRACE 0 works always.

I understand your concern about to reduce the expose attach surface.
BTW, it will be there with telemetry too.
Disabling full feature  for the code via config/rte_config.h is new to
DPDK. I think, we need wider opinion on this(Adding techboard).
Also, DPDK never concerned with binary size. Other than binary size,
following patch and exposed the config through meson
will fix the other problems. IMO, That's the correct tradeoff.


#define __rte_trace_point_emit_header_generic(t) \
void *mem; \
do { \
  +      if (RTE_TRACE == 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)

>
>  /* 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..fd864125a7 100644
> --- a/lib/eal/include/rte_trace_point.h
> +++ b/lib/eal/include/rte_trace_point.h
> @@ -42,6 +42,8 @@ typedef RTE_ATOMIC(uint64_t) rte_trace_point_t;
>   */
>  #define RTE_TRACE_POINT_ARGS
>
> +#ifdef RTE_TRACE
> +
>  /** @internal Helper macro to support RTE_TRACE_POINT and RTE_TRACE_POINT_FP */
>  #define __RTE_TRACE_POINT(_mode, _tp, _args, ...) \
>  extern rte_trace_point_t __##_tp; \
> @@ -100,6 +102,20 @@ _tp _args \
>  #define RTE_TRACE_POINT_FP(tp, args, ...) \
>         __RTE_TRACE_POINT(fp, tp, args, __VA_ARGS__)
>
> +#else
> +
> +/** @internal Helper macro to support RTE_TRACE_POINT and RTE_TRACE_POINT_FP */
> +#define __RTE_TRACE_POINT_VOID(_tp, ...) \
> +static __rte_always_inline void \
> +_tp(...) \
> +{ \
> +}
> +
> +#define RTE_TRACE_POINT(tp, args, ...) __RTE_TRACE_POINT_VOID(tp, args)
> +#define RTE_TRACE_POINT_FP(tp, args, ...) __RTE_TRACE_POINT_VOID(tp, args)
> +
> +#endif /* RTE_TRACE */
> +
>  #ifdef __DOXYGEN__
>
>  /**
> @@ -212,6 +228,7 @@ 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 +247,7 @@ __rte_trace_point_fp_is_enabled(void)
>         return false;
>  #endif
>  }
> +#endif /* RTE_TRACE */
>
>  /**
>   * @internal
> @@ -356,6 +374,8 @@ __rte_trace_point_emit_ev_header(void *mem, uint64_t in)
>         return RTE_PTR_ADD(mem, __RTE_TRACE_EVENT_HEADER_SZ);
>  }
>
> +#ifdef RTE_TRACE
> +
>  #define __rte_trace_point_emit_header_generic(t) \
>  void *mem; \
>  do { \
> @@ -411,7 +431,7 @@ 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..567fce534e 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); \
> @@ -56,6 +58,21 @@ do { \
>                 RTE_STR(uint8_t)); \
>  } while (0)
>
> +#else
> +
> +#define RTE_TRACE_POINT_REGISTER(...)
> +#define __rte_trace_point_emit_header_generic(t) RTE_SET_USED(t)
> +#define __rte_trace_point_emit_header_fp(t) RTE_SET_USED(t)
> +#define __rte_trace_point_emit(in, type) RTE_SET_USED(in)
> +#define rte_trace_point_emit_string(in) RTE_SET_USED(in)
> +#define rte_trace_point_emit_blob(in, len) \
> +do { \
> +       RTE_SET_USED(in); \
> +       RTE_SET_USED(len); \
> +} while (0)
> +
> +#endif /* RTE_TRACE */
> +
>  #ifdef __cplusplus
>  }
>  #endif
> --
> 2.43.0
>