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

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Message-ID: <alpine.DEB.2.11.1603122104360.3657@nanos>
Date:	Sat, 12 Mar 2016 21:08:16 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jianyu Zhan <nasa4836@...il.com>
cc:	mingo@...hat.com, hpa@...or.com, Aravind.Gopalakrishnan@....com,
	brgerst@...il.com, bp@...e.de, feng.wu@...el.com,
	jiang.liu@...ux.intel.com, tj@...nel.org, dvlasenk@...hat.com,
	penberg@...helsinki.fi, yhlu.kernel@...il.com, andi@...stfloor.org,
	luto@...nel.org, ajm@....com, yinghai@...nel.org,
	akinobu.mita@...il.com, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] x86/irq: update first_system_vector only when
 X86_LOCAL_PIC is on

On Sat, 12 Mar 2016, Jianyu Zhan wrote:

> During native_init_IRQ(), we will update first_system_vector conditionally
> when we init system vector. But on !CONFIG_X86_LOCAL_PIC, we prefer it
> to NR_IRQS, so don't bother set it on this case.
> 
> Signed-off-by: Jianyu Zhan <nasa4836@...il.com>
> ---
>  arch/x86/include/asm/desc.h | 2 ++
>  arch/x86/kernel/irqinit.c   | 3 ---
>  2 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
> index 4e10d73..4fc2deb 100644
> --- a/arch/x86/include/asm/desc.h
> +++ b/arch/x86/include/asm/desc.h
> @@ -383,8 +383,10 @@ static inline void alloc_system_vector(int vector)
>  {
>  	if (!test_bit(vector, used_vectors)) {
>  		set_bit(vector, used_vectors);
> +#ifdef CONFIG_X86_LOCAL_APIC
>  		if (first_system_vector > vector)
>  			first_system_vector = vector;
> +#endif

This is pointless, because it's only called when local apic is enabled as all
call sites of alloc_intr_gate() depend on CONFIG_X86_LOCAL_APIC ....

>  	} else {
>  		BUG();
>  	}
> diff --git a/arch/x86/kernel/irqinit.c b/arch/x86/kernel/irqinit.c
> index 0e9fa7c..e999b38 100644
> --- a/arch/x86/kernel/irqinit.c
> +++ b/arch/x86/kernel/irqinit.c
> @@ -188,9 +188,6 @@ void __init native_init_IRQ(void)
>  	 * 'special' SMP interrupts)
>  	 */
>  	i = FIRST_EXTERNAL_VECTOR;
> -#ifndef CONFIG_X86_LOCAL_APIC
> -#define first_system_vector NR_VECTORS
> -#endif
>  	for_each_clear_bit_from(i, used_vectors, first_system_vector) {

And how exactly is this here supposed to compile when CONFIG_X86_LOCAL_APIC=n?

>  		/* IA32_SYSCALL_VECTOR could be used in trap_init already. */
>  		set_intr_gate(i, irq_entries_start +
> -- 
> 2.4.3
> 
>