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

[Jerin Jacob <jerinjacobk@gmail.com>]

On Thu, Sep 19, 2024 at 9:05 PM Morten Brørup <mb@smartsharesystems.com> wrote:
>
> > Could you share data with a real-world application of the elf size?
> > 1)Without any change
>
> Size of the statically linked executable on the target file system:
> 3,800,528 byte
>
> > 2)Only disabling via __rte_trace_point_emit_header_generic() .. aka below
> > patch.
>
> 3,572,032 byte
>
> > 3)Full disable.
>
> 3,572,032 byte
>
> >
> > I think, size command will spit out with different section's size.
> > This data can be used to take decision and to know how much % it
> > adding up?
>
> I.e. trace adds 228,496 byte = 6.4 % to the size of this specific executable.
>
> ~200 KB might not seem as much, but this is just omitting one module.
> If other unused modules also add ~200 KB, it adds up.
>
> And I haven't done any significant additional memory footprint tuning.
>
>
> > > > #define __rte_trace_point_emit_header_generic(t) \
> > > > void *mem; \
> > > > do { \
> > > >   +      if (RTE_TRACE == 0) \
> > > >   +             return \
>
> Tested without the RTE_TRACE==0 check, simply:
>   void *mem; \
>   do { \
> +         return; \
>           const uint64_t val = rte_atomic_load_explicit(t, rte_memory_order_acquire); \
>
> > > >         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 don't understand why your method uses as little memory as mine...

Compiler is start enough to understand those functions are NOP.


> My method should also omit the trace points themselves, with their names and numbers, and their initialization.
>
> I haven't looked deeper into it.
>
> If your method of omitting trace is as efficient as all my ifdefs, I also prefer your method.
> Simpler is better.
>