linux-kernel - Re: [rfc patch v4.4-rt2] sched: fix up preempt lazy forward port

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Date:	Tue, 19 Jan 2016 03:29:57 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: [rfc patch v4.4-rt2] sched: fix up preempt lazy forward port

On Mon, 2016-01-18 at 21:18 +0100, Sebastian Andrzej Siewior wrote:

> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -3542,6 +3542,15 @@ asmlinkage __visible void __sched notrac
> > 	if (likely(!preemptible()))
> > 		return;
> > 
> > +#ifdef CONFIG_PREEMPT_LAZY
> > +	/*
> > +	 * Check for lazy preemption
> > +	 */
> > +	if (current_thread_info()->preempt_lazy_count &&
> > +	    !test_thread_flag(TIF_NEED_RESCHED))
> > +		return;
> > +#endif
> > +
> 
> And this is a new piece. So you forbid that tasks leave the CPU if
> lazy_count > 0. Let me look closed why this is happening and if this is
> v4.1 … v4.4 or not.

We should probably just add the lazy bits to preemptible().

	-Mike