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SubjectRe: [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@infradead.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@infradead.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@infradead.org>

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

-- Steve

> Cc: Julian Anastasov <ja@ssi.bg>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: NeilBrown <neilb@suse.de>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h


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