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

[Steven Rostedt]

On Fri, 5 Jun 2015 18:10:21 +0200
Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> 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@xxxxxxxxxxxxx>

Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>

-- Steve

>     Cc: Julian Anastasov <ja@xxxxxx>
>     Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>     Cc: NeilBrown <neilb@xxxxxxx>
>     Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
>     Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>     Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>     Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
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