linux-kernel - Re: [RFC PATCH 09/18] kthread: Make it easier to correctly sleep in iterant kthreads

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Message-ID: <20150608134810.3abd862b@gandalf.local.home>
Date:	Mon, 8 Jun 2015 13:48:10 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Petr Mladek <pmladek@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Richard Weinberger <richard@....at>,
	David Woodhouse <dwmw2@...radead.org>,
	linux-mtd@...ts.infradead.org,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	Anna Schumaker <anna.schumaker@...app.com>,
	linux-nfs@...r.kernel.org, Chris Mason <clm@...com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>, Borislav Petkov <bp@...e.de>,
	Michal Hocko <mhocko@...e.cz>, live-patching@...r.kernel.org,
	linux-api@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 09/18] kthread: Make it easier to correctly sleep in
 iterant kthreads

On Fri, 5 Jun 2015 18:10:21 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Fri, Jun 05, 2015 at 05:01:08PM +0200, Petr Mladek wrote:
> > Many kthreads go into an interruptible sleep when there is nothing
> > to do. They should check if anyone did not requested the kthread
> > to terminate, freeze, or park in the meantime. It is easy to do
> > it a wrong way.
> 
> INTERRUPTIBLE is the wrong state to idle in for kthreads, use
> TASK_IDLE.
> 
> ---
> 
> commit 80ed87c8a9ca0cad7ca66cf3bbdfb17559a66dcf
> Author: Peter Zijlstra <peterz@...radead.org>
> Date:   Fri May 8 14:23:45 2015 +0200
> 
>     sched/wait: Introduce TASK_NOLOAD and TASK_IDLE
>     
>     Currently people use TASK_INTERRUPTIBLE to idle kthreads and wait for
>     'work' because TASK_UNINTERRUPTIBLE contributes to the loadavg. Having
>     all idle kthreads contribute to the loadavg is somewhat silly.

Not to mention, tasks in TASK_UNINTERRUPTIBLE state for too long will
trigger hung task detection.


>     
>     Now mostly this works OK, because kthreads have all their signals
>     masked. However there's a few sites where this is causing problems and
>     TASK_UNINTERRUPTIBLE should be used, except for that loadavg issue.
>     
>     This patch adds TASK_NOLOAD which, when combined with
>     TASK_UNINTERRUPTIBLE avoids the loadavg accounting.
>     
>     As most of imagined usage sites are loops where a thread wants to
>     idle, waiting for work, a helper TASK_IDLE is introduced.
>     
>     Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

>     Cc: Julian Anastasov <ja@....bg>
>     Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>     Cc: NeilBrown <neilb@...e.de>
>     Cc: Oleg Nesterov <oleg@...hat.com>
>     Cc: Peter Zijlstra <peterz@...radead.org>
>     Cc: Thomas Gleixner <tglx@...utronix.de>
>     Signed-off-by: Ingo Molnar <mingo@...nel.org>
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
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