linux-kernel - [RFC PATCH v2 0/3] report task state in symbolic chars from sched tracepoint

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Message-Id: <20230726121618.19198-1-zegao@tencent.com>
Date:   Wed, 26 Jul 2023 20:16:15 +0800
From:   Ze Gao <zegao2021@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Namhyung Kim <namhyung@...nel.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>,
        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: [RFC PATCH v2 0/3] report task state in symbolic chars from sched tracepoint

This is the 2nd attempt to fix the report task state issue in sched
tracepint, here is the first version:

https://lore.kernel.org/linux-trace-kernel/20230725072254.32045-1-zegao@tencent.com

Against v1, add a new var to report task state in symbolic char instead
of replacing the old one and to not to break anything.

--

In the status quo, we should see three different outcomes of the reported
sched-out task state from perf-script, perf-sched-timehist, and Tp_printk
of tracepoint sched_switch.  And it's not hard to figure out that the
former two are built upon the third one, and the reason why we see this
inconsistency is that the former two does not catch up with the internal
change of reported task state definitions as the kernel evolves.

IMHO, exporting internal representations of task state in the tracepoint
sched_switch is not a good practice and not encouraged at all, which can
easily break userspace tools that relies on it. Especially when tracepoints
are massively used in many observability tools nowadays due to its stable
nature, which makes them no longer used for debug only purpose and we
should be careful to decide what ought to be reported to userspace and what
ought not.

Therefore, to fix the issues mentioned above for good, instead of choosing
I proposed to add a new variable to report task state in sched_switch with
a symbolic character along with the old hardcoded value, and save the
further processing of userspace tools and spare them from knowing
implementation details in the kernel.

After this patch seires, we report 'RSDTtXZPI' the same as in procfs, plus
a 'p' which denotes PREEMP_ACTIVE and is used for sched_switch tracepoint only.

Reviews welcome!

Regards,

Ze

Ze Gao (2):
  sched, tracing: add to report task state in symbolic chars
  perf sched: use the new prev_state_char instead in tracepoint
    sched_switch

 include/trace/events/sched.h | 60 +++++++++++++++++++++---------------
 tools/perf/builtin-sched.c   | 57 ++++++----------------------------
 2 files changed, 45 insertions(+), 72 deletions(-)

Ze Gao (1):
  libtraceevent: use the new prev_state_char instead in tracepoint
    sched_switch

 plugins/plugin_sched_switch.c | 29 ++++-------------------------
 1 file changed, 4 insertions(+), 25 deletions(-)

-- 
2.40.1