linux-kernel - Re: [PATCH 04/12] perf/x86/intel: Support CPUID 10.ECX to disable fixed counters

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Date:   Tue, 26 Jan 2021 16:53:15 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
Cc:     acme@...nel.org, mingo@...nel.org, linux-kernel@...r.kernel.org,
        eranian@...gle.com, namhyung@...nel.org, jolsa@...hat.com,
        ak@...ux.intel.com, yao.jin@...ux.intel.com
Subject: Re: [PATCH 04/12] perf/x86/intel: Support CPUID 10.ECX to disable
 fixed counters

On Tue, Jan 19, 2021 at 12:38:23PM -0800, kan.liang@...ux.intel.com wrote:
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index a54d4a9..21267dc 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -5206,7 +5209,7 @@ __init int intel_pmu_init(void)
>  	union cpuid10_eax eax;
>  	union cpuid10_ebx ebx;
>  	struct event_constraint *c;
> -	unsigned int unused;
> +	unsigned int fixed_mask;
>  	struct extra_reg *er;
>  	bool pmem = false;
>  	int version, i;
> @@ -5228,7 +5231,7 @@ __init int intel_pmu_init(void)
>  	 * Check whether the Architectural PerfMon supports
>  	 * Branch Misses Retired hw_event or not.
>  	 */
> -	cpuid(10, &eax.full, &ebx.full, &unused, &edx.full);
> +	cpuid(10, &eax.full, &ebx.full, &fixed_mask, &edx.full);
>  	if (eax.split.mask_length < ARCH_PERFMON_EVENTS_COUNT)
>  		return -ENODEV;
>  
> @@ -5255,8 +5258,16 @@ __init int intel_pmu_init(void)
>  	if (version > 1) {
>  		int assume = 3 * !boot_cpu_has(X86_FEATURE_HYPERVISOR);
>  
> -		x86_pmu.num_counters_fixed =
> -			max((int)edx.split.num_counters_fixed, assume);
> +		if (!fixed_mask) {
> +			x86_pmu.num_counters_fixed =
> +				max((int)edx.split.num_counters_fixed, assume);
> +		} else {
> +			/*
> +			 * The fixed-purpose counters are enumerated in the ECX
> +			 * since V5 perfmon.
> +			 */
> +			x86_pmu.num_counters_fixed = fls(fixed_mask);
> +		}
>  	}
>  
>  	if (version >= 4)
> @@ -5847,8 +5858,11 @@ __init int intel_pmu_init(void)
>  		x86_pmu.num_counters_fixed = INTEL_PMC_MAX_FIXED;
>  	}
>  
> -	x86_pmu.intel_ctrl |=
> -		((1LL << x86_pmu.num_counters_fixed)-1) << INTEL_PMC_IDX_FIXED;
> +	if (!fixed_mask) {
> +		x86_pmu.intel_ctrl |=
> +			((1LL << x86_pmu.num_counters_fixed)-1) << INTEL_PMC_IDX_FIXED;
> +	} else
> +		x86_pmu.intel_ctrl |= (u64)fixed_mask << INTEL_PMC_IDX_FIXED;
>  
>  	/* AnyThread may be deprecated on arch perfmon v5 or later */
>  	if (x86_pmu.intel_cap.anythread_deprecated)

Maybe like so.

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index fe940082d49a..274d75d33c14 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -4766,7 +4766,7 @@ __init int intel_pmu_init(void)
 	union cpuid10_eax eax;
 	union cpuid10_ebx ebx;
 	struct event_constraint *c;
-	unsigned int unused;
+	unsigned int fixed_mask;
 	struct extra_reg *er;
 	bool pmem = false;
 	int version, i;
@@ -4788,7 +4788,7 @@ __init int intel_pmu_init(void)
 	 * Check whether the Architectural PerfMon supports
 	 * Branch Misses Retired hw_event or not.
 	 */
-	cpuid(10, &eax.full, &ebx.full, &unused, &edx.full);
+	cpuid(10, &eax.full, &ebx.full, &fixed_mask, &edx.full);
 	if (eax.split.mask_length < ARCH_PERFMON_EVENTS_COUNT)
 		return -ENODEV;
 
@@ -4812,11 +4812,18 @@ __init int intel_pmu_init(void)
 	 * Quirk: v2 perfmon does not report fixed-purpose events, so
 	 * assume at least 3 events, when not running in a hypervisor:
 	 */
-	if (version > 1) {
+	if (version > 1 && version < 5) {
 		int assume = 3 * !boot_cpu_has(X86_FEATURE_HYPERVISOR);
 
 		x86_pmu.num_counters_fixed =
 			max((int)edx.split.num_counters_fixed, assume);
+
+		fixed_mask = (1L << x86_pmu.num_counters_fixed) - 1;
+
+	} else if (version >= 5 ) {
+
+		x86_pmu.num_counters_fixed = fls(fixed_mask);
+
 	}
 
 	if (boot_cpu_has(X86_FEATURE_PDCM)) {
@@ -5366,8 +5373,7 @@ __init int intel_pmu_init(void)
 		x86_pmu.num_counters_fixed = INTEL_PMC_MAX_FIXED;
 	}
 
-	x86_pmu.intel_ctrl |=
-		((1LL << x86_pmu.num_counters_fixed)-1) << INTEL_PMC_IDX_FIXED;
+	x86_pmu.intel_ctrl |= (u64)fixed_mask << INTEL_PMC_IDX_FIXED;
 
 	/* AnyThread may be deprecated on arch perfmon v5 or later */
 	if (x86_pmu.intel_cap.anythread_deprecated)