linux-kernel - Re: [PATCH v3 08/11] perf/x86: Enable NMI source reporting for perfmon

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Message-ID: <f5ec09c0-db5e-4c2f-b516-964e8d7eb2af@linux.intel.com>
Date: Thu, 4 Jul 2024 10:44:23 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Jacob Pan <jacob.jun.pan@...ux.intel.com>, X86 Kernel <x86@...nel.org>,
 Sean Christopherson <seanjc@...gle.com>, LKML
 <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>,
 Dave Hansen <dave.hansen@...el.com>, "H. Peter Anvin" <hpa@...or.com>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Xin Li <xin3.li@...el.com>, linux-perf-users@...r.kernel.org,
 Peter Zijlstra <peterz@...radead.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Tony Luck <tony.luck@...el.com>,
 Andy Lutomirski <luto@...nel.org>, acme@...nel.org,
 Andi Kleen <andi.kleen@...el.com>, "Mehta, Sohil" <sohil.mehta@...el.com>,
 Zeng Guang <guang.zeng@...el.com>
Subject: Re: [PATCH v3 08/11] perf/x86: Enable NMI source reporting for
 perfmon



On 2024-06-28 4:18 p.m., Jacob Pan wrote:
> Program the designated NMI source vector into the performance monitoring
> interrupt (PMI) of the local vector table. PMI handler will be directly
> invoked when its NMI is generated. This avoids the latency of calling all
> NMI handlers blindly.
> 
> Co-developed-by: Zeng Guang <guang.zeng@...el.com>
> Signed-off-by: Zeng Guang <guang.zeng@...el.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> 
> ---
> v3: Program NMI source vector in PVTPC unconditionally (HPA)
> v2: Fix a compile error apic_perfmon_ctr is undefined in i386 config
> ---
>  arch/x86/events/core.c       | 6 ++++--
>  arch/x86/events/intel/core.c | 6 +++---
>  arch/x86/include/asm/apic.h  | 1 +
>  3 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 1ef2201e48ac..be75bdcdd400 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 +1724,8 @@ void perf_events_lapic_init(void)
>  	/*
>  	 * Always use NMI for PMU
>  	 */
> -	apic_write(APIC_LVTPC, APIC_DM_NMI);
> +	apic_perfmon_ctr |= NMI_SOURCE_VEC_PMI;
> +	apic_write(APIC_LVTPC, apic_perfmon_ctr);


It looks like the same value is written unconditionally.

Why not use a macro, e.g., APIC_DM_NMI_WITH_SOURCE, to replace the variable?

Thanks,
Kan

>  }
>  
>  static int
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 38c1b1f1deaa..b4a70457c678 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3093,7 +3093,7 @@ 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, apic_perfmon_ctr);
>  	intel_bts_disable_local();
>  	cpuc->enabled = 0;
>  	__intel_pmu_disable_all(true);
> @@ -3130,7 +3130,7 @@ 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, apic_perfmon_ctr);
>  	/* Only restore PMU state when it's active. See x86_pmu_disable(). */
>  	cpuc->enabled = pmu_enabled;
>  	if (pmu_enabled)
> @@ -3143,7 +3143,7 @@ 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, apic_perfmon_ctr);
>  	return handled;
>  }
>  
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index 9327eb00e96d..bcf8d17240c8 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -49,6 +49,7 @@ static inline void x86_32_probe_apic(void) { }
>  #endif
>  
>  extern u32 cpuid_to_apicid[];
> +extern u32 apic_perfmon_ctr;
>  
>  #define CPU_ACPIID_INVALID	U32_MAX
>