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Date: Tue, 11 Jun 2024 12:10:52 -0700
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Subject: Re: [PATCH v2 5/6] perf/x86: Enable NMI source reporting for perfmon
To: Jacob Pan <jacob.jun.pan@linux.intel.com>, X86 Kernel <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Dave Hansen <dave.hansen@intel.com>, Ingo Molnar <mingo@redhat.com>,
        Borislav Petkov <bp@alien8.de>, linux-perf-users@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>
Cc: Andi Kleen <andi.kleen@intel.com>, Xin Li <xin3.li@intel.com>,
        Zeng Guang <guang.zeng@intel.com>
References: <20240611165457.156364-1-jacob.jun.pan@linux.intel.com>
 <20240611165457.156364-6-jacob.jun.pan@linux.intel.com>
Content-Language: en-US
From: "H. Peter Anvin" <hpa@zytor.com>
In-Reply-To: <20240611165457.156364-6-jacob.jun.pan@linux.intel.com>
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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.

	-hpa