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

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Date:	Thu, 23 Apr 2015 09:12:39 +0200
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Mike Galbraith <umgwanakikbuti@...il.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 2015-04-23 09:01, Mike Galbraith wrote:
> 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.

Hope is good - but not enough here: it breaks the build under
!CONFIG_X, even the case without the bool var.

  CC      kernel/irq_work.o
In file included from ../include/asm-generic/percpu.h:6:0,
                 from ../arch/x86/include/asm/percpu.h:522,
                 from ../arch/x86/include/asm/current.h:5,
                 from ../arch/x86/include/asm/processor.h:15,
                 from ../arch/x86/include/asm/irq_work.h:4,
                 from ../include/linux/irq_work.h:47,
                 from ../kernel/irq_work.c:11:
../kernel/irq_work.c: In function ‘irq_work_queue_on’:
../kernel/irq_work.c:85:17: error: ‘hirq_work_list’ undeclared (first use in this function)
        &per_cpu(hirq_work_list, cpu));

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
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