Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 31 Jul 2023 11:36:55 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Ze Gao <zegao2021@gmail.com>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Ian Rogers <irogers@google.com>,
        Ingo Molnar <mingo@redhat.com>, Jiri Olsa <jolsa@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
        linux-trace-kernel@vger.kernel.org,
        linux-trace-devel@vger.kernel.org, Ze Gao <zegao@tencent.com>
Subject: Re: [RFC PATCH v2 1/3] sched, tracing: add to report task state in
 symbolic chars
Message-ID: <20230731093655.GC29590@hirez.programming.kicks-ass.net>
References: <20230726121618.19198-1-zegao@tencent.com>
 <20230726121618.19198-2-zegao@tencent.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230726121618.19198-2-zegao@tencent.com>
Precedence: bulk

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.