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

From: Peter Zijlstra <peterz@infradead.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>, Tejun Heo <tj@kernel.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dmitry Vyukov <dvyukov@google.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] sched/debug: Use terse backtrace for idly sleeping threads.
Date: Thu, 19 Jul 2018 15:46:53 +0200	[thread overview]
Message-ID: <20180719134653.GH2476@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1532007443-3538-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>

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.