linux-kernel - Re: [RFC PATCH v2 3/3] libtraceevent: use the new prev_state_char instead in tracepoint sched

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Message-ID: <CAD8CoPB1hRZb5eRWBxw3SRH+Hcd7JWfDNqGMadB4+5mibJ17qg@mail.gmail.com>
Date:   Tue, 1 Aug 2023 09:36:56 +0800
From:   Ze Gao <zegao2021@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org,
        linux-trace-devel@...r.kernel.org, Ze Gao <zegao@...cent.com>
Subject: Re: [RFC PATCH v2 3/3] libtraceevent: use the new prev_state_char
 instead in tracepoint sched_switch

Roger that!

Thanks,
Ze

On Mon, Jul 31, 2023 at 11:40 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Wed, 26 Jul 2023 20:16:18 +0800
> Ze Gao <zegao2021@...il.com> wrote:
>
> > Since the sched_switch tracepoint introduces a new variable to
> > report sched-out task state in symbolic char, we switch to use
> > that instead to spare from knowing internal implementations
> > in kernel.
>
> This needs to be changed to check if the "prev_state_char" field exists,
> and if not, then it must use the old method. Same for perf. The tools must
> work with older kernels.
>
> -- Steve
>
> >
> > Signed-off-by: Ze Gao <zegao@...cent.com>
> > ---
> >  plugins/plugin_sched_switch.c | 29 ++++-------------------------
> >  1 file changed, 4 insertions(+), 25 deletions(-)
> >
> > diff --git a/plugins/plugin_sched_switch.c b/plugins/plugin_sched_switch.c
> > index 8752cae..5dbdc28 100644
> > --- a/plugins/plugin_sched_switch.c
> > +++ b/plugins/plugin_sched_switch.c
> > @@ -9,27 +9,6 @@
> >  #include "event-parse.h"
> >  #include "trace-seq.h"
> >
> > -static void write_state(struct trace_seq *s, int val)
> > -{
> > -     const char states[] = "SDTtZXxW";
> > -     int found = 0;
> > -     int i;
> > -
> > -     for (i = 0; i < (sizeof(states) - 1); i++) {
> > -             if (!(val & (1 << i)))
> > -                     continue;
> > -
> > -             if (found)
> > -                     trace_seq_putc(s, '|');
> > -
> > -             found = 1;
> > -             trace_seq_putc(s, states[i]);
> > -     }
> > -
> > -     if (!found)
> > -             trace_seq_putc(s, 'R');
> > -}
> > -
> >  static void write_and_save_comm(struct tep_format_field *field,
> >                               struct tep_record *record,
> >                               struct trace_seq *s, int pid)
> > @@ -97,10 +76,10 @@ static int sched_switch_handler(struct trace_seq *s,
> >       trace_seq_printf(s, "%lld ", val);
> >
> >       if (tep_get_field_val(s, event, "prev_prio", record, &val, 1) ==
> > 0)
> > -             trace_seq_printf(s, "[%d] ", (int) val);
> > +             trace_seq_printf(s, "[%d] ", (short) val);
> >
> > -     if (tep_get_field_val(s,  event, "prev_state", record, &val, 1)
> > == 0)
> > -             write_state(s, val);
> > +     if (tep_get_field_val(s,  event, "prev_state_char", record,
> > &val, 1) == 0)
> > +             trace_seq_putc(s, (char) val);
> >
> >       trace_seq_puts(s, " ==> ");
> >
> > @@ -115,7 +94,7 @@ static int sched_switch_handler(struct trace_seq *s,
> >       trace_seq_printf(s, "%lld", val);
> >
> >       if (tep_get_field_val(s, event, "next_prio", record, &val, 1) ==
> > 0)
> > -             trace_seq_printf(s, " [%d]", (int) val);
> > +             trace_seq_printf(s, " [%d]", (short) val);
> >
> >       return 0;
> >  }
>