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From: Jianyu Zhan <nasa4836@gmail.com>
Date: Sun, 13 Mar 2016 17:29:15 +0800
Message-ID: <CAHz2CGWDYHoAWQVNxJm+AZkPWN23mOQeR_GQMoybsFoYO9qssg@mail.gmail.com>
Subject: Re: [PATCH 3/3] x86/irq: update first_system_vector only when
 X86_LOCAL_PIC is on
To: Thomas Gleixner <tglx@linutronix.de>
Cc: mingo@redhat.com, "H. Peter Anvin" <hpa@zytor.com>,
        Aravind.Gopalakrishnan@amd.com, brgerst@gmail.com, bp@suse.de,
        feng.wu@intel.com, jiang.liu@linux.intel.com,
        Tejun Heo <tj@kernel.org>, dvlasenk@redhat.com, penberg@cs.helsinki.fi,
        Yinghai Lu <yhlu.kernel@gmail.com>, andi@firstfloor.org,
        Andy Lutomirski <luto@kernel.org>, ajm@sgi.com,
        Yinghai Lu <yinghai@kernel.org>, Akinobu Mita <akinobu.mita@gmail.com>,
        x86@kernel.org, LKML <linux-kernel@vger.kernel.org>
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On Sun, Mar 13, 2016 at 5:11 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Sun, 13 Mar 2016, Jianyu Zhan wrote:
>> On Sun, Mar 13, 2016 at 3:55 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
>> > if LOCAL_APIC is disabled it does not use the interrupt, simply because there
>> > is no way to trigger it. That setup is inside #ifdef CONFIG_X86_LOCAL_APIC for
>> > exactly that reason.
>> >
>> > Just because IRQ_WORK has no config dependency on LOCAL APIC that does not
>> > mean it uses the interrupt gate unconditionally.
>> >
>>
>> Thanks for clarification.
>>
>> I think IRQ_WORK works as generic hardirq context callbacks, it should reply on
>> self IPI,  which is a functionality provided by LOCAL_APIC, while
>> legacy PIC doesn't
>> provide this(correct?).
>
> As I said before IRQ_WORK can work w/o APIC. And therefor IRQ_WORK does NOT
> depend on APIC.
>
> End of story. Nothing to change here at all.

If so, then it is weird, because in current code, IRQ_WORK vector init
is surrounded by
CONFIG_X86_LOCAL_APIC.  And actually my patch did move it out.

After all,  thanks for all the clarifications :-).

Regards,
Jianyu Zhan