linux-kernel - Re: [RFC PATCH v4 4/7] sched, tracing: reorganize fields of switch event struct

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Date:   Thu, 3 Aug 2023 10:02:04 +0800
From:   Ze Gao <zegao2021@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     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>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.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 v4 4/7] sched, tracing: reorganize fields of switch
 event struct

On Wed, Aug 2, 2023 at 11:05 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Wed,  2 Aug 2023 08:09:59 -0400
> Ze Gao <zegao2021@...il.com> wrote:
>
> > From: Ze Gao <zegao2021@...il.com>
> >
> > Report priorities in 'short' and prev_state in 'int' to save
> > some buffer space. And also reorder the fields so that we take
> > struct alignment into consideration to make the record compact.
> >
> > Suggested-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> > Signed-off-by: Ze Gao <zegao@...cent.com>
> > ---
> >  include/trace/events/sched.h | 24 ++++++++++++------------
> >  1 file changed, 12 insertions(+), 12 deletions(-)
> >
> > diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> > index fbb99a61f714..7d34db20b2c6 100644
> > --- a/include/trace/events/sched.h
> > +++ b/include/trace/events/sched.h
> > @@ -187,7 +187,7 @@ DEFINE_EVENT(sched_wakeup_template, sched_wakeup_new,
> >            TP_ARGS(p));
> >
> >  #ifdef CREATE_TRACE_POINTS
> > -static inline long __trace_sched_switch_state(bool preempt,
> > +static inline int __trace_sched_switch_state(bool preempt,
> >                                             unsigned int prev_state,
> >                                             struct task_struct *p)
> >  {
> > @@ -229,23 +229,23 @@ TRACE_EVENT(sched_switch,
> >       TP_ARGS(preempt, prev, next, prev_state),
> >
> >       TP_STRUCT__entry(
> > -             __array(        char,   prev_comm,      TASK_COMM_LEN   )
> >               __field(        pid_t,  prev_pid                        )
> > -             __field(        int,    prev_prio                       )
> > -             __field(        long,   prev_state                      )
> > -             __array(        char,   next_comm,      TASK_COMM_LEN   )
> >               __field(        pid_t,  next_pid                        )
> > -             __field(        int,    next_prio                       )
> > +             __field(        short,  prev_prio                       )
> > +             __field(        short,  next_prio                       )
> > +             __field(        int,    prev_state                      )
>
> I was talking with Peter on IRC and since the biggest number that
> prev_state can be is TASK_REPORT_MASK which is 0x100, I think we can make
> prev_state into a short as well.

Make sense, let's change it to short.

Regards,
Ze