linux-kernel - Re: [PATCH 3/3] x86/irq: update first_system_vector only when X86_LOCAL

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Date:	Sun, 13 Mar 2016 17:29:15 +0800
From:	Jianyu Zhan <nasa4836@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	mingo@...hat.com, "H. Peter Anvin" <hpa@...or.com>,
	Aravind.Gopalakrishnan@....com, brgerst@...il.com, bp@...e.de,
	feng.wu@...el.com, jiang.liu@...ux.intel.com,
	Tejun Heo <tj@...nel.org>, dvlasenk@...hat.com,
	penberg@...helsinki.fi, Yinghai Lu <yhlu.kernel@...il.com>,
	andi@...stfloor.org, Andy Lutomirski <luto@...nel.org>,
	ajm@....com, Yinghai Lu <yinghai@...nel.org>,
	Akinobu Mita <akinobu.mita@...il.com>, x86@...nel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] x86/irq: update first_system_vector only when
 X86_LOCAL_PIC is on

On Sun, Mar 13, 2016 at 5:11 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Sun, 13 Mar 2016, Jianyu Zhan wrote:
>> On Sun, Mar 13, 2016 at 3:55 PM, Thomas Gleixner <tglx@...utronix.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