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

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Message-ID: <20150706135733.GK17217@hawk.localdomain>
Date:	Mon, 6 Jul 2015 15:57:33 +0200
From:	Andrew Jones <drjones@...hat.com>
To:	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 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.

Thanks,
drew
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