linux-kernel - Re: [v5 3/3] x86, irq: Define a global vector for VT-d Posted-Interrupts

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Date:	Mon, 18 May 2015 16:17:47 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Feng Wu <feng.wu@...el.com>
cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	jiang.liu@...ux.intel.com
Subject: Re: [v5 3/3] x86, irq: Define a global vector for VT-d
 Posted-Interrupts

On Mon, 18 May 2015, Feng Wu wrote:
> diff --git a/arch/x86/include/asm/hardirq.h b/arch/x86/include/asm/hardirq.h
> index 0f5fb6b..9866065 100644
> --- a/arch/x86/include/asm/hardirq.h
> +++ b/arch/x86/include/asm/hardirq.h
> @@ -14,6 +14,7 @@ typedef struct {
>  #endif
>  #ifdef CONFIG_HAVE_KVM
>  	unsigned int kvm_posted_intr_ipis;
> +	unsigned int kvm_posted_intr_wakeup_ipis;

So now we have another IPI with statistics and nothing which makes it
accessible. kvm_posted_intr_ipis lacks a printout in
arch_show_interrupts() as well.

>  #ifdef CONFIG_HAVE_KVM
> +void (*wakeup_handler_callback)(void);
> +EXPORT_SYMBOL_GPL(wakeup_handler_callback);
> +

The naming sucks. Which wakeup?

As this is kvm specific, it should have a kvm_ prefix. And it should
tell what it actually does: 
     
     kvm_posted_intr_wakeup_handler

Hmm?

>  /*
>   * Handler for POSTED_INTERRUPT_VECTOR.
>   */
> @@ -256,6 +259,26 @@ __visible void smp_kvm_posted_intr_ipi(struct pt_regs *regs)
>  
>  	set_irq_regs(old_regs);
>  }
> +
> +/*
> + * Handler for POSTED_INTERRUPT_WAKEUP_VECTOR.
> + */
> +__visible void smp_kvm_posted_intr_wakeup_ipi(struct pt_regs *regs)
> +{
> +	struct pt_regs *old_regs = set_irq_regs(regs);
> +
> +	entering_ack_irq();
> +
> +	inc_irq_stat(kvm_posted_intr_wakeup_ipis);
> +
> +	if (wakeup_handler_callback)
> +		wakeup_handler_callback();

Why do we need a conditional here?

staic void dummy_handler(void) { }
static void *kvm_posted_intr_wakeup_handler = dummy_handler;

void kvm_set_posted_intr_wakeup_handler(void (*handler)(void))
{
	if (handler)
		kvm_posted_intr_wakeup_handler = handler;
	else
		kvm_posted_intr_wakeup_handler = dummy_handler;
}

avoids the conditional in the exception handler....

Thanks,

	tglx
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