linux-kernel - Re: [RFC PATCH] sched/debug: Use terse backtrace for idly sleeping threads.

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Date:   Thu, 19 Jul 2018 15:46:53 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tejun Heo <tj@...nel.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] sched/debug: Use terse backtrace for idly sleeping
 threads.

On Thu, Jul 19, 2018 at 10:37:23PM +0900, Tetsuo Handa wrote:
> This patch can be applied before proposing abovementioned changes.
> Since there are many kernel threads whose backtrace is boring due to idly
> waiting for an event inside the main loop, this patch introduces a kernel
> config option (which allows SysRq-t to use one-liner backtrace for threads
> idly waiting for an event) and simple helpers (which allow current thread
> to declare that current thread is about to start/end idly waiting).

> diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
> index f776807..6b8c8bd 100644
> --- a/drivers/base/devtmpfs.c
> +++ b/drivers/base/devtmpfs.c
> @@ -406,7 +406,9 @@ static int devtmpfsd(void *p)
>  		}
>  		__set_current_state(TASK_INTERRUPTIBLE);
>  		spin_unlock(&req_lock);
> +		start_idle_sleeping();
>  		schedule();
> +		end_idle_sleeping();
>  	}
>  	return 0;
>  out:

So I _really_ hate the idea of sprinking that all around the kernel like
this.