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

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

> From: Jerin Jacob [mailto:jerinjacobk@gmail.com]
> Sent: Thursday, 19 September 2024 10.52
> 
> 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 agree it's not pretty, but it's the best solution I can come up with, to meet the requirements driving this patch: reducing attack surface and memory footprint.

> 
> I understand your concern about to reduce the expose attach surface.
> BTW, it will be there with telemetry too.

Yes, I have telemetry in mind too. :-)
Got to work on them one by one, though.

> 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).

Yes, it’s a good topic for discussion in the techboard.

Currently, there are three levels of build-time configuration:
1. Meson, for prominent options.
2. config/rte_config.h for less prominent options, e.g. enabling RTE_ASSERT(), mempool statistics, etc.
3. Header files in various modules/drivers, for tweaking the individual module.

There didn't seem to be any interest in enabling/disabling trace via Meson, so I chose the next level of configuration.

> Also, DPDK never concerned with binary size.

That is a big mistake. DPDK is not only for cloud.
DPDK should also be for CPEs, SOHO firewalls, and similar network appliances. For some of these high-volume network appliances, memory footprint matters.

Also, when running many instances of a service in the cloud, power consumption matters. Bloat increases power consumption.

> Other than binary size,
> following patch and exposed the config through meson
> will fix the other problems. IMO, That's the correct tradeoff.

Yes; the optimal solution would be making EAL less bloated, i.e. purely an abstraction layer to the underlying hardware and O/S.
This would make trace an independent module, which could be enabled/disabled through Meson.

Bruce has contributed a lot in this area, and already made many modules optional.

> 
> 
> #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
> >