linux-kernel - [tip: perf/core] perf/x86/amd/core: Detect available counters

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Date:   Fri, 29 Apr 2022 20:28:51 -0000
From:   "tip-bot2 for Sandipan Das" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Sandipan Das <sandipan.das@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: perf/core] perf/x86/amd/core: Detect available counters

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     baf0f4a6733095d7443a07e5db5525376c1c9bd5
Gitweb:        https://git.kernel.org/tip/baf0f4a6733095d7443a07e5db5525376c1c9bd5
Author:        Sandipan Das <sandipan.das@....com>
AuthorDate:    Thu, 21 Apr 2022 11:16:56 +05:30
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 29 Apr 2022 11:06:27 +02:00

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/68a6d9688df189267db26530378870edd34f7b06.1650515382.git.sandipan.das@amd.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 b70dfa0..52fd794 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 8199fc5..c6cc07f 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;
@@ -368,6 +380,11 @@ struct pebs_xmm {
 };
 
 /*
+ * AMD Extended Performance Monitoring and Debug cpuid feature detection
+ */
+#define EXT_PERFMON_DEBUG_FEATURES		0x80000022
+
+/*
  * IBS cpuid feature detection
  */