linux-kernel - Re: [PATCH] x86/sched/dynamic-ticks: Call new schedule_irq_disable() for scheduling in entry

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Message-ID: <1368147092.7373.148.camel@gandalf.local.home>
Date:	Thu, 09 May 2013 20:51:32 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86/sched/dynamic-ticks: Call new
 schedule_irq_disable() for scheduling in entry_64.S

On Thu, 2013-05-09 at 20:47 -0400, Steven Rostedt wrote:

> > 
> > > +
> > > +	local_irq_enable();
> > > +	__schedule();
> > 
> > Are you sure it's fine to call __schedule() instead of schedule()?
> > I don't know much about the blk work to handle there but it may be
> > worth considering.
> 
> Note, this isn't a call to schedule that was made by normal kernel
> space. This is very much like a preemption. In fact, it is a preemption
> and my first patch used preempt_schedule_irq() instead, but as that's
> made for CONFIG_PREEMPT enabled, it seemed a bit hacky to take that out
> of that context.
> 
> This is only called when the task is being preempted. But because its
> going to user land, its OK. The blk code there is more worried about
> something that did some work, set itself to TASK_UNINTERRUPTIBLE and
> then called schedule() (think completions). That is, the blk code that
> needs to be submitted will be the code that wakes up this task.
> 
> We should never be in anything but TASK_RUNNING when going into user
> space.

Maybe I should rename this function to schedule_user() to explicitly
show that this is for scheduling when we came from or going to user
space.

-- Steve


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