linux-kernel - Re: [PATCH v2 5/6] perf/x86: Enable NMI source reporting for perfmon

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Date: Wed, 12 Jun 2024 13:27:41 -0700
From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: X86 Kernel <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Thomas
 Gleixner <tglx@...utronix.de>, Dave Hansen <dave.hansen@...el.com>, Ingo
 Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 linux-perf-users@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
 Andi Kleen <andi.kleen@...el.com>, Xin Li <xin3.li@...el.com>, Zeng Guang
 <guang.zeng@...el.com>, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v2 5/6] perf/x86: Enable NMI source reporting for
 perfmon

Hi H.,

On Tue, 11 Jun 2024 12:10:52 -0700, "H. Peter Anvin" <hpa@...or.com> wrote:

> On 6/11/24 09:54, Jacob Pan wrote:
> > 
> > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> > index 1ef2201e48ac..db8c30881f5c 100644
> > --- a/arch/x86/events/core.c
> > +++ b/arch/x86/events/core.c
> > @@ -46,6 +46,7 @@
> >   
> >   struct x86_pmu x86_pmu __read_mostly;
> >   static struct pmu pmu;
> > +u32 apic_perfmon_ctr = APIC_DM_NMI;
> >   
> >   DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events) = {
> >   	.enabled = 1,
> > @@ -1680,7 +1681,7 @@ int x86_pmu_handle_irq(struct pt_regs *regs)
> >   	 * This generic handler doesn't seem to have any issues where
> > the
> >   	 * unmasking occurs so it was left at the top.
> >   	 */
> > -	apic_write(APIC_LVTPC, APIC_DM_NMI);
> > +	apic_write(APIC_LVTPC, apic_perfmon_ctr);
> >   
> >   	for (idx = 0; idx < x86_pmu.num_counters; idx++) {
> >   		if (!test_bit(idx, cpuc->active_mask))
> > @@ -1723,7 +1724,10 @@ void perf_events_lapic_init(void)
> >   	/*
> >   	 * Always use NMI for PMU
> >   	 */
> > -	apic_write(APIC_LVTPC, APIC_DM_NMI);
> > +	if (cpu_feature_enabled(X86_FEATURE_NMI_SOURCE))
> > +		apic_perfmon_ctr |= NMI_SOURCE_VEC_PMI;
> > +
> > +	apic_write(APIC_LVTPC, apic_perfmon_ctr);
> >   }
> >  
> There really is no reason to not do this unconditinoally. If NMI source 
> is not supported it is simply a noop.
Yes, will do.

I was being paranoid in case some old CPUs don't ignore the vector field.

Thanks,

Jacob