linux-kernel - Re: [PATCH 1/7] perf tools: Track all user changed config bits

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Message-ID: <20251202112147.GT724103@e132581.arm.com>
Date: Tue, 2 Dec 2025 11:21:47 +0000
From: Leo Yan <leo.yan@....com>
To: James Clark <james.clark@...aro.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Mike Leach <mike.leach@...aro.org>,
	John Garry <john.g.garry@...cle.com>, Will Deacon <will@...nel.org>,
	Leo Yan <leo.yan@...ux.dev>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, coresight@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/7] perf tools: Track all user changed config bits

On Tue, Dec 02, 2025 at 10:40:49AM +0000, James Clark wrote:
> 
> 
> On 02/12/2025 10:15 am, Leo Yan wrote:
> > On Mon, Dec 01, 2025 at 04:41:04PM +0000, Coresight ML wrote:
> > 
> > [...]
> > 
> > > +#define ADD_CONFIG_CHG(format_type, term_type, new_term)		\
> > > +{									\
> > > +	struct parse_events_term *term;					\
> > > +	u64 bits = 0;							\
> > > +	int type;							\
> > > +									\
> > > +	list_for_each_entry(term, &head_config->terms, list) {		\
> > > +		if (term->type_term == PARSE_EVENTS__TERM_TYPE_USER) {  \
> > > +			type = perf_pmu__format_type(pmu, term->config);\
> > > +			if (type != format_type)			\
> > > +				continue;				\
> > > +			bits |= perf_pmu__format_bits(pmu, term->config); \
> > > +		} else if (term->type_term == term_type) {		\
> > > +			bits = ~(u64)0;					\
> > > +		}							\
> > > +	}								\
> > > +									\
> > > +	if (bits)							\
> > > +		ADD_CONFIG_TERM_VAL(new_term, cfg_chg, bits, false);	\
> > > +	return 0;							\
> > 
> > Nitpick: "return 0" is not needed here.  Otherwise:
> > 
> > Reviewed-by: Leo Yan <leo.yan@....com>
> 
> I think it's worse than not needed, it makes it stop collecting the changes
> after the first one.

Just curious how this can happen.

  foo()
  {
      {
          chunk 1;
      }

      {
          chunk 2;
      }
  }

Seem to me, if without "return 0" in chunk 1, it still can continue to
run chunk 2, no?

> It was annoying that this had to be a macro instead of a function because
> ADD_CONFIG_TERM_VAL constructs the #define name of the first argument.
> 
> It's probably worth putting in some effort to make ADD_CONFIG_CHG() a
> function to avoid problems like this and maybe add a test.

This would be fine for me.

Thanks,
Leo