linux-kernel - Re: [PATCH v3 2/6] scripts: python: Extact necessary information from process event

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Message-ID: <CAP-5=fW0DT+JkU07K8brv2O_T6=hTM3SQMoji0o2rnsF6w+Y_Q@mail.gmail.com>
Date:   Wed, 12 Jul 2023 10:03:57 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Anup Sharma <anupnewsmail@...il.com>
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>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/6] scripts: python: Extact necessary information from
 process event

On Wed, Jul 12, 2023 at 10:01 AM Ian Rogers <irogers@...gle.com> wrote:
>
> On Mon, Jul 10, 2023 at 4:10 PM Anup Sharma <anupnewsmail@...il.com> wrote:
> >
> > The script takes in a sample event dictionary(param_dict) and retrieves
> > relevant data such as time stamp, PID, TID, thread name. Also start time
> > is defined.
> >
> > Signed-off-by: Anup Sharma <anupnewsmail@...il.com>
> > ---
> >  .../perf/scripts/python/firefox-gecko-converter.py  | 13 ++++++++++++-
> >  1 file changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/scripts/python/firefox-gecko-converter.py b/tools/perf/scripts/python/firefox-gecko-converter.py
> > index 5b342641925c..765f1775cee5 100644
> > --- a/tools/perf/scripts/python/firefox-gecko-converter.py
> > +++ b/tools/perf/scripts/python/firefox-gecko-converter.py
> > @@ -21,8 +21,19 @@ sys.path.append(os.environ['PERF_EXEC_PATH'] + \
> >  from perf_trace_context import *
> >  from Core import *
> >
>
> It'd be nice to have a comment here, perhaps:
> # The time stamp from the first of the time ordered events.
>
> > +start_time = None
> > +
> >  def trace_end():
> >         pass
> >
> >  def process_event(param_dict):
> > -       pass
> > +       global start_time
> > +       # Extract relevant information from the event parameters. The event parameters
> > +       # are in a dictionary:
> > +       time_stamp = (param_dict['sample']['time'] // 1000) / 1000
> > +       pid = param_dict['sample']['pid']
> > +       tid = param_dict['sample']['tid']
> > +       thread_name = param_dict['comm']
> > +
> > +       # Assume that start time is the time of the first event.
> > +       start_time = time_stamp if not start_time else start_time
>
> I appreciate that this is one line, but it takes some getting your
> head around that start_time is being assigned to itself in the common
> case. I think this would be more readable as:
>
> if not start_time:
>   start_time = time_stamp

I believe the events are guaranteed time ordered in perf script. The
ordered_event logic handles this, but I likely haven't got a full
grasp on all the corners of it. You can always assert the behavior
(comments with guarantees :-) ):

assert start_time <= time_stamp, "Events aren't time ordered"

Thanks,
Ian

> Thanks,
> Ian
>
> > --
> > 2.34.1
> >