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

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Message-ID: <710bd9c4-efa4-444e-8699-5a6430e8d6be@amd.com>
Date: Thu, 8 May 2025 16:50:05 +0530
From: Sandipan Das <sandipan.das@....com>
To: Sohil Mehta <sohil.mehta@...el.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Cc: Xin Li <xin@...or.com>, "H . Peter Anvin" <hpa@...or.com>,
 Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Peter Zijlstra <peterz@...radead.org>,
 Sean Christopherson <seanjc@...gle.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Kan Liang <kan.liang@...ux.intel.com>, Tony Luck <tony.luck@...el.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Vitaly Kuznetsov <vkuznets@...hat.com>,
 "Rafael J . Wysocki" <rafael@...nel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, Zhang Rui <rui.zhang@...el.com>,
 Lukasz Luba <lukasz.luba@....com>, Steven Rostedt <rostedt@...dmis.org>,
 Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Brian Gerst <brgerst@...il.com>, Andrew Cooper <andrew.cooper3@...rix.com>,
 "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
 Jacob Pan <jacob.pan@...ux.microsoft.com>, Andi Kleen <ak@...ux.intel.com>,
 Kai Huang <kai.huang@...el.com>, Nikolay Borisov <nik.borisov@...e.com>,
 linux-perf-users@...r.kernel.org, linux-edac@...r.kernel.org,
 kvm@...r.kernel.org, linux-pm@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v5 8/9] perf/x86: Enable NMI-source reporting for perfmon

On 5/7/2025 6:51 AM, Sohil Mehta wrote:
> From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> 
> 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@...el.com>
> Signed-off-by: Zeng Guang <guang.zeng@...el.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Signed-off-by: Sohil Mehta <sohil.mehta@...el.com>
> Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>
> ---
> 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@....com>