linux-kernel - Re: [RFC PATCH 2/3] docs: scheduler: Add scheduler overview documentation

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Message-ID: <jhjv9mjjp5p.mognet@arm.com>
Date:   Wed, 01 Apr 2020 14:45:06 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Daniel Bristot de Oliveira <bristot@...hat.com>,
        John Mathew <john.mathew@...kie.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        corbet@....net, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        tsbogend@...ha.franken.de, lukas.bulwahn@...il.com, x86@...nel.org,
        linux-mips@...r.kernel.org, tglx@...utronix.de,
        mostafa.chamanara@...emark.com
Subject: Re: [RFC PATCH 2/3] docs: scheduler: Add scheduler overview documentation


On Wed, Apr 01 2020, Peter Zijlstra wrote:
> On Wed, Apr 01, 2020 at 01:47:04PM +0200, Daniel Bristot de Oliveira wrote:
>> On 4/1/20 12:35 PM, Peter Zijlstra wrote:
>> >> +Scheduler State Transition
>> >> +==========================
>> >> +
>> >> +A very high level scheduler state transition flow with a few states can be
>> >> +depicted as follows.
>> >> +
>> >> +.. kernel-render:: DOT
>> >> +   :alt: DOT digraph of Scheduler state transition
>> >> +   :caption: Scheduler state transition
>> >> +
>> >> +   digraph sched_transition {
>> >> +      node [shape = point,  label="exisiting task\n calls fork()"]; fork
>> >> +      node [shape = box, label="TASK_NEW\n(Ready to run)"] tsk_new;
>> >> +      node [shape = box, label="TASK_RUNNING\n(Ready to run)"] tsk_ready_run;
>> >> +      node [shape = box, label="TASK_RUNNING\n(Running)"] tsk_running;
>> >> +      node [shape = box, label="TASK_DEAD\nEXIT_ZOMBIE"] exit_zombie;
>> >> +      node [shape = box, label="TASK_INTERRUPTIBLE\nTASK_UNINTERRUPTIBLE\nTASK_WAKEKILL"] tsk_int;
>> >> +      fork -> tsk_new [ label = "task\nforks" ];
>> >> +      tsk_new -> tsk_ready_run;
>> >> +      tsk_ready_run -> tsk_running [ label = "schedule() calls context_switch()" ];
>> >> +      tsk_running -> tsk_ready_run [ label = "task is pre-empted" ];
>> >> +      subgraph int {
>> >> +         tsk_running -> tsk_int [ label = "task needs to wait for event" ];
>> >> +         tsk_int ->  tsk_ready_run [ label = "event occurred" ];
>> >> +      }
>> >> +      tsk_int ->  exit_zombie [ label = "task exits via do_exit()" ];
>> >> +   }
>> > And that is a prime example of why I hates RST, it pretty much mandates
>> > you view this with something other than a text editor.
>>
>> The good thing about the dot format is that we can convert it to many other
>> formats, including text:
>
> Oh, I know and love dot files, I generate them occasionally. But they
> stink as end-result, which is what it is here.
>
> If you can't read a document (or worse comment) in a code editor it's
> broken (and yes, I know some subsystems have a different opinion here).

Agreed. Feel free to use dot to draw stuff, but please include the textual
version in the doc. If you really insist on having a fancier image in the
web output, have a look at things like ditaa (or whatever equivalent is
supported in rst).