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

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Date:   Tue, 1 Aug 2023 13:34:01 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ze Gao <zegao2021@...il.com>
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>,
        Steven Rostedt <rostedt@...dmis.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, Aug 01, 2023 at 05:01:21PM +0800, Ze Gao wrote:
> Internal representations of task state are likely to be changed
> or ordered, and reporting them to userspace without exporting
> them as part of API is basically wrong, which can easily break
> a userspace observability tool as kernel evolves. For example,
> perf suffers from this and still reports wrong states as of this
> writing.
> 
> OTOH, some masqueraded states like TASK_REPORT_IDLE and
> TASK_REPORT_MAX are also reported inadvertently, which confuses
> things even more and most userspace tools do not even take them
> into consideration.
> 
> So add a new variable in company with the old raw value to
> report task state in symbolic chars, which are self-explaining
> and no further translation is needed. Of course this does not
> break any userspace tool.
> 
> Note for PREEMPT_ACTIVE, we introduce 'p' to report it and use
> the old conventions for the rest.

*sigh*... just because userspace if daft, we need to change the kernel?

Why do we need this character anyway, why not just print the state in
hex and leave it at that? These single character state things are a
relic, please just let them die.