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

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Date:	Mon, 06 Jul 2015 11:02:37 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Andrew Jones <drjones@...hat.com>, Ingo Molnar <mingo@...nel.org>
CC:	Vitaly Kuznetsov <vkuznets@...hat.com>, 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>
Subject: Re: [PATCH] x86/irq: hide HYP in /proc/interrupts when not on Xen/Hyper-V

On 07/06/2015 09:57 AM, Andrew Jones wrote:
> On Sat, Jul 04, 2015 at 10:26:53AM +0200, Ingo Molnar wrote:
>> * 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.
> This is a good point. When virt stuff creeps out, it's easy to lose track of
> it. But, I would prefer that vmware and kvm guests don't have to have a
> meaningless counter in /proc/interrupts. Also, for xen, I see that it only
> matters for x86. ARM xen builds would also have a meaningless counter. Maybe
> we should add a flags member to hypervisor_x86, and start using that in
> these types of situations.

This is all x86 arch code so I don't see how it will make any difference 
to Xen on ARM.


-boris

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