linux-kernel - Re: [RFC PATCH v3 3/6] sched, tracing: add to report task state in symbolic chars

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Message-ID: <20230801102729.71906f13@gandalf.local.home>
Date:   Tue, 1 Aug 2023 10:27:29 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ze Gao <zegao2021@...il.com>,
        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>,
        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 v3 3/6] sched, tracing: add to report task state in
 symbolic chars

On Tue, 1 Aug 2023 13:45:45 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, Aug 01, 2023 at 05:01:21PM +0800, Ze Gao wrote:
> > @@ -233,6 +255,7 @@ TRACE_EVENT(sched_switch,
> >  		__field(	pid_t,	prev_pid			)
> >  		__field(	int,	prev_prio			)
> >  		__field(	long,	prev_state			)
> > +		__field(	char,	prev_state_char			)
> >  		__array(	char,	next_comm,	TASK_COMM_LEN	)
> >  		__field(	pid_t,	next_pid			)
> >  		__field(	int,	next_prio			)  
> 
> And this again will wreck everybody that consumes the raw tracepoint
> without looking at tracefs.

Nobody does that anymore, as the events change constantly, and are
different on different kernels. Powertop (the tool that caused us pain
before by using raw values) had to break down and use libtraceevent,
because it would break if there was a 32 bit version running on a 64 bit
kernel.

I've changed the offsets of raw events a few times and nobody has
complained since.

-- Steve