linux-kernel - Re: [RFC PATCH 1/3] sched, tracing: report task state in symbolic chars instead

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Message-ID: <20230725133100.GL3765278@hirez.programming.kicks-ass.net>
Date:   Tue, 25 Jul 2023 15:31:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ze Gao <zegao2021@...il.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, Ze Gao <zegao@...cent.com>
Subject: Re: [RFC PATCH 1/3] sched, tracing: report task state in symbolic
 chars instead

On Tue, Jul 25, 2023 at 06:53:07PM +0800, Ze Gao wrote:

> > > @@ -232,7 +235,7 @@ TRACE_EVENT(sched_switch,
> > >               __array(        char,   prev_comm,      TASK_COMM_LEN   )
> > >               __field(        pid_t,  prev_pid                        )
> > >               __field(        int,    prev_prio                       )
> > > -             __field(        long,   prev_state                      )
> > > +             __field(        char,   prev_state                      )
> > >               __array(        char,   next_comm,      TASK_COMM_LEN   )
> > >               __field(        pid_t,  next_pid                        )
> > >               __field(        int,    next_prio                       )
> >
> > This is a format change and will likely break a ton of programs :/
> 

> BTW, could you help to point to any possible tools/programs that would
> break other than perf/libtraceevent, because these two are the only
> users I run into so far.

Latencytop was the one breaking a few years ago, but there's a metric
ton of sched_switch users out there, this is bound to generate pain.

Steve, you remember what the status of all this was? at the time
breaking this was considered on par with ABI breakage and we reverted or
something. Is this still so?