Re: [PATCH RFC v3 02/12] perf jevents: Add support for system events tables

[Jiri Olsa]

On Mon, May 11, 2020 at 09:21:00AM -0700, Ian Rogers wrote:

SNIP

> >  >> +           fprintf(outfp, "\n\t{\n\t\t.table = %s,\n\t},",
> >  >> +                   sys_event_table->name);
> >  >> +   }
> >  >> +   fprintf(outfp, "\n\t{\n\t\t.table = 0\n\t},");
> >  >
> >  > this will add extra tabs:
> >  >
> >  >          {
> >  >                  .table = 0
> >  >          },
> >  >
> >  > while the rest of the file starts items without any indent
> >  >
> >
> > I'll ensure the indent is the same.
> >
> > BTW, is there anything to be said for removing the empty map feature
> > (and always breaking the perf build instead)? I guess that it was just
> > an early feature for dealing with unstable JSONs.
> 
> +1
> I'd very much like it if JSON parse errors and the like didn't result
> in an empty map but failed the build. I think ideally we could also

yep, that seems like good approach to me

> validate metric expressions using expr.y. If we include expr.y into
> jevents then is there any need to parse the metric expression at
> runtime? Could we just generate C code from jevents with a list of
> events (aka ids) for programming and a dedicated print function for
> each metric. The events would still be symbolic and checked at
> runtime, but the expressions being C code could yield compile time
> errors.

nice idea.. not sure we are able to do that with just expr.y code,
like to generate specific C code for metric, but I'd like to see
patches for that ;-)

but we would still need expr.y int perf code for custom user metrics,
so it still needs to stay anyway

jirka