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

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Date:	Tue, 19 Jan 2016 06:14:43 +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 Tue, 2016-01-19 at 05:41 +0100, Mike Galbraith wrote:
> 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.
> 
> That check wants a !rt_task(current) qualifier anyway.

(bah, -ESWILLMORECOFFEE)