linux-kernel - Re: [PATCH 1/2] perf/x86/intel: Don't clear perf metrics overflow bit unconditionally

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Message-ID: <7666eeaf-930c-4c4b-bcb8-9767feff10f6@linux.intel.com>
Date: Tue, 15 Apr 2025 14:47:51 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Andi Kleen <ak@...ux.intel.com>, Eranian Stephane <eranian@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
 Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [PATCH 1/2] perf/x86/intel: Don't clear perf metrics overflow bit
 unconditionally



On 2025-04-15 6:41 a.m., Dapeng Mi wrote:
> The below code would always unconditionally clear other status bits like
> perf metrics overflow bit once PEBS buffer overflows.
> 
>         status &= intel_ctrl | GLOBAL_STATUS_TRACE_TOPAPMI;
> 
> This is incorrect. Perf metrics overflow bit should be cleared only when
> fixed counter 3 in PEBS counter group. Otherwise perf metrics overflow
> could be missed to handle.
> 
> Closes: https://lore.kernel.org/all/20250225110012.GK31462@noisy.programming.kicks-ass.net/
> Fixes: 7b2c05a15d29 ("perf/x86/intel: Generic support for hardware TopDown metrics")
> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>

For the two patches,

Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>

Thanks,
Kan

> ---
>  arch/x86/events/intel/core.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 0ceaa1b07019..c6f69ce3b2b3 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3140,7 +3140,6 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
>  	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
>  	int bit;
>  	int handled = 0;
> -	u64 intel_ctrl = hybrid(cpuc->pmu, intel_ctrl);
>  
>  	inc_irq_stat(apic_perf_irqs);
>  
> @@ -3184,7 +3183,6 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
>  		handled++;
>  		x86_pmu_handle_guest_pebs(regs, &data);
>  		static_call(x86_pmu_drain_pebs)(regs, &data);
> -		status &= intel_ctrl | GLOBAL_STATUS_TRACE_TOPAPMI;
>  
>  		/*
>  		 * PMI throttle may be triggered, which stops the PEBS event.
> @@ -3195,6 +3193,15 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
>  		 */
>  		if (pebs_enabled != cpuc->pebs_enabled)
>  			wrmsrl(MSR_IA32_PEBS_ENABLE, cpuc->pebs_enabled);
> +
> +		/*
> +		 * Above PEBS handler (PEBS counters snapshotting) has updated fixed
> +		 * counter 3 and perf metrics counts if they are in counter group,
> +		 * unnecessary to update again.
> +		 */
> +		if (cpuc->events[INTEL_PMC_IDX_FIXED_SLOTS] &&
> +		    is_pebs_counter_event_group(cpuc->events[INTEL_PMC_IDX_FIXED_SLOTS]))
> +			status &= ~GLOBAL_STATUS_PERF_METRICS_OVF_BIT;
>  	}
>  
>  	/*
> @@ -3214,6 +3221,8 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
>  		static_call(intel_pmu_update_topdown_event)(NULL, NULL);
>  	}
>  
> +	status &= hybrid(cpuc->pmu, intel_ctrl);
> +
>  	/*
>  	 * Checkpointed counters can lead to 'spurious' PMIs because the
>  	 * rollback caused by the PMI will have cleared the overflow status
> 
> base-commit: 5c3627b6f0595f1ec27e6f5df903bd072e9b9136