linux-kernel - Re: [RFC PATCH v2 1/3] sched, tracing: add to report task state in symbolic chars

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Message-ID: <20230731093655.GC29590@hirez.programming.kicks-ass.net>
Date:   Mon, 31 Jul 2023 11:36:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ze Gao <zegao2021@...il.com>
Cc:     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 1/3] sched, tracing: add to report task state in
 symbolic chars

On Wed, Jul 26, 2023 at 08:16:16PM +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 not a good choice, which can easily break a userspace
> observability tool as kernel evolves. For example, perf suffers from
> this and still reports wrong states by this patch.
> 
> OTOH, some masqueraded state like TASK_REPORT_IDLE and TASK_REPORT_MAX
> are also reported inadvertently, which confuses things even more.
> 
> So add a new variable in company with the old raw value to report task
> state in symbolic char, which is self-explaining and no further
> translation is needed, and also report priorities in 'short' to save
> some buffer space.  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.

So I really dont much like this. This looses the ability to see the
actual wait state flags, there could be multiple. Eg, things like
TASK_FREEZEABLE gets lost completely.

And this is on top of my reluctance to touch any of this at all, for
fear of further regressions.