Re: [PATCH v3] eal: add build-time option to omit trace

[Jerin Jacob <jerinjacobk@gmail.com>]

On Fri, Sep 20, 2024 at 2:38 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>
> ---
> 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             | 11 ++++++++++-
>  config/rte_config.h               |  1 +
>  lib/eal/include/rte_trace_point.h | 21 +++++++++++++++++++++
>  3 files changed, 32 insertions(+), 1 deletion(-)
>
> 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)

Now that, we are is not disabling any symbols,
This conditional compilation can be removed. Use
__rte_trace_point_generic_is_enabled() in another leg.


> +
> +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..b80688ce89 100644
> --- a/lib/eal/include/rte_trace_point.h
> +++ b/lib/eal/include/rte_trace_point.h
> @@ -212,6 +212,25 @@ bool rte_trace_point_is_enabled(rte_trace_point_t *tp);
>  __rte_experimental
>  rte_trace_point_t *rte_trace_point_lookup(const char *name);
>
> +/**
> + * @internal
> + *
> + * Test if the tracepoint compile-time option is enabled.
> + *
> + * @return
> + *   true if tracepoint enabled, false otherwise.
> + */
> +__rte_experimental
> +static __rte_always_inline bool
> +__rte_trace_point_generic_is_enabled(void)

Add to version.map file

> +{
> +#ifdef RTE_TRACE
> +       return true;
> +#else
> +       return false;
> +#endif
> +}
> +
>  /**
>   * @internal
>   *
> @@ -359,6 +378,8 @@ __rte_trace_point_emit_ev_header(void *mem, uint64_t in)
>  #define __rte_trace_point_emit_header_generic(t) \
>  void *mem; \
>  do { \
> +       if (!__rte_trace_point_generic_is_enabled()) \
> +               return; \


To be super safe, Add similar check in
RTE_INIT(trace##_init)

>         const uint64_t val = rte_atomic_load_explicit(t, rte_memory_order_acquire); \
>         if (likely(!(val & __RTE_TRACE_FIELD_ENABLE_MASK))) \
>                 return; \
> --
> 2.43.0
>