linux-kernel - Re: [PATCH RT 3.18] irq_work: Provide a soft-irq based queue

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Date:	Thu, 23 Apr 2015 09:01:22 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	RT <linux-rt-users@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RT 3.18] irq_work: Provide a soft-irq based queue

On Thu, 2015-04-23 at 08:50 +0200, Jan Kiszka wrote:
> On 2015-04-23 08:11, Mike Galbraith wrote:
> > @@ -103,6 +98,9 @@ EXPORT_SYMBOL_GPL(irq_work_queue_on);
> >  /* Enqueue the irq work @work on the current CPU */
> >  bool irq_work_queue(struct irq_work *work)
> >  {
> > +       bool realtime = IS_ENABLED(CONFIG_PREEMPT_RT_FULL);
> > +       bool raise = false;
> > +
> >         /* Only queue if not already pending */
> >         if (!irq_work_claim(work))
> >                 return false;
> > @@ -110,25 +108,22 @@ bool irq_work_queue(struct irq_work *wor
> >         /* Queue the entry and raise the IPI if needed. */
> >         preempt_disable();
> >  
> > -#ifdef CONFIG_PREEMPT_RT_FULL
> > -       if (work->flags & IRQ_WORK_HARD_IRQ) {
> > +       if (realtime && (work->flags & IRQ_WORK_HARD_IRQ)) {
> >                 if (llist_add(&work->llnode, 
> > this_cpu_ptr(&hirq_work_list)))
> 
> This boils down to
> 
> #ifdef CONFIG_X
> some_type x;
> #endif
> ...
> 
> if (IS_ENABLED(CONFIG_X) && ...)
>       use(x);
> 
> And here we even have an indirection for IS_ENABLED via that local 
> bool
> variable. Is that pattern OK for Linux? Does it compile in all 
> supported
> optimization levels of all supported compilers?

I hope it all goes away, that being what IS_ENABLED() is there for.

        -Mike
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