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

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Date:	Tue, 07 Jul 2015 14:40:50 +0200
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
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

Ingo Molnar <mingo@...nel.org> writes:

> * 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.

I was under an impression KVM and Vmware don't use these hypervisor
callback irqs 'by desing' and even if one day they start using it
someone will have to put inc_irq_stat() somewhere.

If the goal is to avoid having x86_hyper_ms_hyperv/x86_hyper_xen in
irq.c we can follow Andrew's suggestion and add a flag
(use_callback_irqs?) to struct hypervisor_x86.

Thanks,

-- 
  Vitaly
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