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

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Message-ID: <20200401122606.GF20713@hirez.programming.kicks-ass.net>
Date:   Wed, 1 Apr 2020 14:26:06 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     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 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).