linux-kernel - [PATCH v2 4/7] perf/x86/amd/core: Detect available counters

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Date:   Thu, 21 Apr 2022 11:16:56 +0530
From:   Sandipan Das <sandipan.das@....com>
To:     <linux-kernel@...r.kernel.org>, <linux-perf-users@...r.kernel.org>,
        <x86@...nel.org>
CC:     <peterz@...radead.org>, <bp@...en8.de>,
        <dave.hansen@...ux.intel.com>, <acme@...nel.org>,
        <mark.rutland@....com>, <alexander.shishkin@...ux.intel.com>,
        <namhyung@...nel.org>, <jolsa@...nel.org>, <tglx@...utronix.de>,
        <mingo@...hat.com>, <pbonzini@...hat.com>, <jmattson@...gle.com>,
        <like.xu.linux@...il.com>, <eranian@...gle.com>,
        <ananth.narayan@....com>, <ravi.bangoria@....com>,
        <santosh.shukla@....com>, <sandipan.das@....com>
Subject: [PATCH v2 4/7] perf/x86/amd/core: Detect available counters

If AMD Performance Monitoring Version 2 (PerfMonV2) is
supported, use CPUID leaf 0x80000022 EBX to detect the
number of Core PMCs. This offers more flexibility if the
counts change in later processor families.

Signed-off-by: Sandipan Das <sandipan.das@....com>
---
 arch/x86/events/amd/core.c        |  6 ++++++
 arch/x86/include/asm/perf_event.h | 17 +++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index b70dfa028ba5..52fd7941a724 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -1186,6 +1186,7 @@ static const struct attribute_group *amd_attr_update[] = {
 
 static int __init amd_core_pmu_init(void)
 {
+	union cpuid_0x80000022_ebx ebx;
 	u64 even_ctr_mask = 0ULL;
 	int i;
 
@@ -1206,9 +1207,14 @@ static int __init amd_core_pmu_init(void)
 
 	/* Check for Performance Monitoring v2 support */
 	if (boot_cpu_has(X86_FEATURE_PERFMON_V2)) {
+		ebx.full = cpuid_ebx(EXT_PERFMON_DEBUG_FEATURES);
+
 		/* Update PMU version for later usage */
 		x86_pmu.version = 2;
 
+		/* Find the number of available Core PMCs */
+		x86_pmu.num_counters = ebx.split.num_core_pmc;
+
 		amd_pmu_global_cntr_mask = (1ULL << x86_pmu.num_counters) - 1;
 	}
 
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index a5dea5da1b52..7aa1d420c779 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -186,6 +186,18 @@ union cpuid28_ecx {
 	unsigned int            full;
 };
 
+/*
+ * AMD "Extended Performance Monitoring and Debug" CPUID
+ * detection/enumeration details:
+ */
+union cpuid_0x80000022_ebx {
+	struct {
+		/* Number of Core Performance Counters */
+		unsigned int	num_core_pmc:4;
+	} split;
+	unsigned int		full;
+};
+
 struct x86_pmu_capability {
 	int		version;
 	int		num_counters_gp;
@@ -372,6 +384,11 @@ struct pebs_xmm {
 	u64 xmm[16*2];	/* two entries for each register */
 };
 
+/*
+ * AMD Extended Performance Monitoring and Debug cpuid feature detection
+ */
+#define EXT_PERFMON_DEBUG_FEATURES		0x80000022
+
 /*
  * IBS cpuid feature detection
  */
-- 
2.32.0