linux-kernel - Re: [PATCH v2 05/12] perf jevents: Support parsing negative exponents

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Date: Wed, 13 Mar 2024 22:35:20 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, John Garry <john.g.garry@...cle.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, Jing Zhang <renyu.zj@...ux.alibaba.com>, 
	Thomas Richter <tmricht@...ux.ibm.com>, James Clark <james.clark@....com>, 
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org, 
	Andi Kleen <ak@...ux.intel.com>, Kajol Jain <kjain@...ux.ibm.com>, 
	Sandipan Das <sandipan.das@....com>, Ravi Bangoria <ravi.bangoria@....com>, 
	Perry Taylor <perry.taylor@...el.com>, Samantha Alt <samantha.alt@...el.com>, 
	Caleb Biggers <caleb.biggers@...el.com>, Weilin Wang <weilin.wang@...el.com>, 
	Edward Baker <edward.baker@...el.com>, Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v2 05/12] perf jevents: Support parsing negative exponents

On Tue, Mar 5, 2024 at 11:20 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Fri, Mar 1, 2024 at 5:00 PM Ian Rogers <irogers@...gle.com> wrote:
> >
> > Support negative exponents when parsing from a json metric string by
> > making the numbers after the 'e' optional in the 'Event' insertion fix
> > up.
> >
> > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > ---
> >  tools/perf/pmu-events/metric.py      | 2 +-
> >  tools/perf/pmu-events/metric_test.py | 4 ++++
> >  2 files changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/pmu-events/metric.py b/tools/perf/pmu-events/metric.py
> > index 847b614d40d5..31eea2f45152 100644
> > --- a/tools/perf/pmu-events/metric.py
> > +++ b/tools/perf/pmu-events/metric.py
> > @@ -573,7 +573,7 @@ def ParsePerfJson(orig: str) -> Expression:
> >    # a double by the Bison parser
> >    py = re.sub(r'0Event\(r"[xX]([0-9a-fA-F]*)"\)', r'Event("0x\1")', py)
> >    # Convert accidentally converted scientific notation constants back
> > -  py = re.sub(r'([0-9]+)Event\(r"(e[0-9]+)"\)', r'\1\2', py)
> > +  py = re.sub(r'([0-9]+)Event\(r"(e[0-9]*)"\)', r'\1\2', py)
>
> I don't understand how it can handle negative numbers.
> Why isn't it like Event\(r"(e-?[0-9]+)"\) ?

When something like 3e12 is converted at this point it would be:
3Event("e12")
and so this substitution remove the Event and puts it back to:
3e12
but it expects a number with the "e". For a negative exponent like 3e-12 we get:
3Event("e")-12
and so there's no number and no substitution. Changing the + to a *
means the number in the event next to the "e" becomes optional and so
we match and remove the Event again.

I'm wondering about having this be a bit more of a parser, but then it
kind of defeats using Python's eval as being the parser.

Thanks,
Ian

> Thanks,
> Namhyung
>
>
> >    # Convert all the known keywords back from events to just the keyword
> >    keywords = ['if', 'else', 'min', 'max', 'd_ratio', 'source_count', 'has_event', 'strcmp_cpuid_str']
> >    for kw in keywords:
> > diff --git a/tools/perf/pmu-events/metric_test.py b/tools/perf/pmu-events/metric_test.py
> > index ee22ff43ddd7..8acfe4652b55 100755
> > --- a/tools/perf/pmu-events/metric_test.py
> > +++ b/tools/perf/pmu-events/metric_test.py
> > @@ -61,6 +61,10 @@ class TestMetricExpressions(unittest.TestCase):
> >      after = before
> >      self.assertEqual(ParsePerfJson(before).ToPerfJson(), after)
> >
> > +    before = r'a + 3e-12 + b'
> > +    after = before
> > +    self.assertEqual(ParsePerfJson(before).ToPerfJson(), after)
> > +
> >    def test_IfElseTests(self):
> >      # if-else needs rewriting to Select and back.
> >      before = r'Event1 if #smt_on else Event2'
> > --
> > 2.44.0.278.ge034bb2e1d-goog
> >