Re: [PATCH v5 8/9] perf/x86: Enable NMI-source reporting for perfmon

[Sandipan Das]

On 5/7/2025 6:51 AM, Sohil Mehta wrote:
> From: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> 
> Program the designated PMI NMI-source vector into the local vector table
> for the PMU. An NMI for the PMU would directly invoke the PMI handler
> without polling other NMI handlers, resulting in reduced PMI delivery
> latency.
> 
> Co-developed-by: Zeng Guang <guang.zeng@xxxxxxxxx>
> Signed-off-by: Zeng Guang <guang.zeng@xxxxxxxxx>
> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> Signed-off-by: Sohil Mehta <sohil.mehta@xxxxxxxxx>
> Reviewed-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> ---
> v5: No significant change.
> ---
>  arch/x86/events/core.c       | 4 ++--
>  arch/x86/events/intel/core.c | 6 +++---
>  arch/x86/include/asm/apic.h  | 1 +
>  3 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 031e908f0d61..42b270526631 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -1695,7 +1695,7 @@ 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, PERF_NMI);
>  
>  	for_each_set_bit(idx, x86_pmu.cntr_mask, X86_PMC_IDX_MAX) {
>  		if (!test_bit(idx, cpuc->active_mask))
> @@ -1737,7 +1737,7 @@ void perf_events_lapic_init(void)
>  	/*
>  	 * Always use NMI for PMU
>  	 */
> -	apic_write(APIC_LVTPC, APIC_DM_NMI);
> +	apic_write(APIC_LVTPC, PERF_NMI);
>  }
>  
>  static int
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 09d2d66c9f21..87c624686c58 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3202,7 +3202,7 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
>  	 * NMI handler.
>  	 */
>  	if (!late_ack && !mid_ack)
> -		apic_write(APIC_LVTPC, APIC_DM_NMI);
> +		apic_write(APIC_LVTPC, PERF_NMI);
>  	intel_bts_disable_local();
>  	cpuc->enabled = 0;
>  	__intel_pmu_disable_all(true);
> @@ -3239,7 +3239,7 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
>  
>  done:
>  	if (mid_ack)
> -		apic_write(APIC_LVTPC, APIC_DM_NMI);
> +		apic_write(APIC_LVTPC, PERF_NMI);
>  	/* Only restore PMU state when it's active. See x86_pmu_disable(). */
>  	cpuc->enabled = pmu_enabled;
>  	if (pmu_enabled)
> @@ -3252,7 +3252,7 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
>  	 * Haswell CPUs.
>  	 */
>  	if (late_ack)
> -		apic_write(APIC_LVTPC, APIC_DM_NMI);
> +		apic_write(APIC_LVTPC, PERF_NMI);
>  	return handled;
>  }
>  
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index 9bade39b5feb..b2f864e77d84 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -29,6 +29,7 @@
>  #define BT_NMI			(APIC_DM_NMI | NMIS_VECTOR_BT)
>  #define KGDB_NMI		(APIC_DM_NMI | NMIS_VECTOR_KGDB)
>  #define MCE_NMI			(APIC_DM_NMI | NMIS_VECTOR_MCE)
> +#define PERF_NMI		(APIC_DM_NMI | NMIS_VECTOR_PMI)
>  
>  /*
>   * Debugging macros

For AMD processors that do not support NMI source reporting but use
x86_pmu_handle_irq() and perf_events_lapic_init()

Tested-by: Sandipan Das <sandipan.das@xxxxxxx>