linux-kernel - Re: [PATCH] x86/irq: hide HYP in /proc/interrupts when not on Xen/Hyper-V

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Date:	Sat, 4 Jul 2015 10:26:53 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Radim Krčmář <rkrcmar@...hat.com>,
	Andrew Jones <drjones@...hat.com>
Subject: Re: [PATCH] x86/irq: hide HYP in /proc/interrupts when not on
 Xen/Hyper-V


* Vitaly Kuznetsov <vkuznets@...hat.com> wrote:

> Hypervisor callback interrupts are only accounted on Xen/Hyper-V and we
> detect hypervisor's type in early boot. There is no point in having
> always-zero HYP: line on other hypervisors or bare metal.
> 
> Suggested-by: Radim Krčmář <rkrcmar@...hat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kernel/irq.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
> index 88b36648..0c82064 100644
> --- a/arch/x86/kernel/irq.c
> +++ b/arch/x86/kernel/irq.c
> @@ -18,6 +18,7 @@
>  #include <asm/mce.h>
>  #include <asm/hw_irq.h>
>  #include <asm/desc.h>
> +#include <asm/hypervisor.h>
>  
>  #define CREATE_TRACE_POINTS
>  #include <asm/trace/irq_vectors.h>
> @@ -139,10 +140,14 @@ int arch_show_interrupts(struct seq_file *p, int prec)
>  	seq_puts(p, "  Machine check polls\n");
>  #endif
>  #if IS_ENABLED(CONFIG_HYPERV) || defined(CONFIG_XEN)
> -	seq_printf(p, "%*s: ", prec, "HYP");
> -	for_each_online_cpu(j)
> -		seq_printf(p, "%10u ", irq_stats(j)->irq_hv_callback_count);
> -	seq_puts(p, "  Hypervisor callback interrupts\n");
> +	if (x86_hyper == &x86_hyper_ms_hyperv ||
> +	    x86_hyper == &x86_hyper_xen) {
> +		seq_printf(p, "%*s: ", prec, "HYP");
> +		for_each_online_cpu(j)
> +			seq_printf(p, "%10u ",
> +				   irq_stats(j)->irq_hv_callback_count);
> +		seq_puts(p, "  Hypervisor callback interrupts\n");
> +	}

So I think we should simplify this to:

	if (x86_hyper) {
		...
	}

this will print the HYP line on hypervisors that don't use 
HYPERVISOR_CALLBACK_VECTOR, but it will make it a lot more self-maintaining, we 
won't accidentally skip this line on hypervisors that start using the callback 
IRQ.

Thanks,

	Ingo
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