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

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Message-Id: <20230731125254.b059f0c7f29761d018dedbe8@kernel.org>
Date:   Mon, 31 Jul 2023 12:52:54 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Ze Gao <zegao2021@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.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 0/3] report task state in symbolic chars from
 sched tracepoint

On Wed, 26 Jul 2023 20:16:15 +0800
Ze Gao <zegao2021@...il.com> wrote:

> 
> 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.

This series looks good to me. Putting the flag in the trace record is
a good idea :)

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

for this series.

Thank you,

> 
> 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
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>