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

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Date:   Thu, 17 Mar 2022 11:58:33 +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 4/7] perf/x86/amd/core: Detect available counters

If AMD Performance Monitoring Version 2 (PerfMonV2) is
supported, use CPUID Fn80000022[EBX] to detect the number
of Core PMCs. This offers more flexibility if the counts
change across processor families.

Signed-off-by: Sandipan Das <sandipan.das@....com>
---
 arch/x86/events/amd/core.c        | 5 +++++
 arch/x86/include/asm/perf_event.h | 8 ++++++++
 2 files changed, 13 insertions(+)

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index a074af97faa9..05d79afe5173 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -980,9 +980,14 @@ static int __init amd_core_pmu_init(void)
 
 	/* Check for Performance Monitoring v2 support */
 	if (boot_cpu_has(X86_FEATURE_PERFMON_V2)) {
+		int ebx = 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 = EXT_PERFMON_DEBUG_NUM_CORE_PMC(ebx);
+
 		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 8fc1b5003713..d7dfef3e998d 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -365,6 +365,14 @@ 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
+
+/* Extended Performance Monitoring and Debug EBX feature bits */
+#define EXT_PERFMON_DEBUG_NUM_CORE_PMC(ebx)	((ebx) & GENMASK(3, 0))
+
 /*
  * IBS cpuid feature detection
  */
-- 
2.32.0