linux-kernel - [tip: perf/urgent] perf/x86/intel: Clean up PEBS-via-PT on hybrid

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Message-ID: <173928636713.10177.3195303394479719181.tip-bot2@tip-bot2>
Date: Tue, 11 Feb 2025 15:06:07 -0000
From: "tip-bot2 for Kan Liang" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Kan Liang <kan.liang@...ux.intel.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf/x86/intel: Clean up PEBS-via-PT on hybrid

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

Commit-ID:     0a5561501397e2bbd0fb0e300eb489f72a90597a
Gitweb:        https://git.kernel.org/tip/0a5561501397e2bbd0fb0e300eb489f72a90597a
Author:        Kan Liang <kan.liang@...ux.intel.com>
AuthorDate:    Wed, 29 Jan 2025 07:48:18 -08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Sat, 08 Feb 2025 15:47:25 +01:00

perf/x86/intel: Clean up PEBS-via-PT on hybrid

The PEBS-via-PT feature is exposed for the e-core of some hybrid
platforms, e.g., ADL and MTL. But it never works.

$ dmesg | grep PEBS
[    1.793888] core: cpu_atom PMU driver: PEBS-via-PT

$ perf record -c 1000 -e '{intel_pt/branch=0/,
cpu_atom/cpu-cycles,aux-output/pp}' -C8
Error:
The sys_perf_event_open() syscall returned with 22 (Invalid argument)
for event (cpu_atom/cpu-cycles,aux-output/pp).
"dmesg | grep -i perf" may provide additional information.

The "PEBS-via-PT" is printed if the corresponding bit of per-PMU
capabilities is set. Since the feature is supported by the e-core HW,
perf sets the bit for e-core. However, for Intel PT, if a feature is not
supported on all CPUs, it is not supported at all. The PEBS-via-PT event
cannot be created successfully.

The PEBS-via-PT is no longer enumerated on the latest hybrid platform. It
will be deprecated on future platforms with Arch PEBS. Let's remove it
from the existing hybrid platforms.

Fixes: d9977c43bff8 ("perf/x86: Register hybrid PMUs")
Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20250129154820.3755948-2-kan.liang@linux.intel.com
---
 arch/x86/events/intel/core.c | 10 ----------
 arch/x86/events/intel/ds.c   | 10 +++++++++-
 2 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 7601196..966f783 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -4941,11 +4941,6 @@ static void intel_pmu_check_hybrid_pmus(struct x86_hybrid_pmu *pmu)
 	else
 		pmu->intel_ctrl &= ~(1ULL << GLOBAL_CTRL_EN_PERF_METRICS);
 
-	if (pmu->intel_cap.pebs_output_pt_available)
-		pmu->pmu.capabilities |= PERF_PMU_CAP_AUX_OUTPUT;
-	else
-		pmu->pmu.capabilities &= ~PERF_PMU_CAP_AUX_OUTPUT;
-
 	intel_pmu_check_event_constraints(pmu->event_constraints,
 					  pmu->cntr_mask64,
 					  pmu->fixed_cntr_mask64,
@@ -5023,9 +5018,6 @@ static bool init_hybrid_pmu(int cpu)
 
 	pr_info("%s PMU driver: ", pmu->name);
 
-	if (pmu->intel_cap.pebs_output_pt_available)
-		pr_cont("PEBS-via-PT ");
-
 	pr_cont("\n");
 
 	x86_pmu_show_pmu_cap(&pmu->pmu);
@@ -6370,11 +6362,9 @@ static __always_inline int intel_pmu_init_hybrid(enum hybrid_pmu_type pmus)
 		pmu->intel_cap.capabilities = x86_pmu.intel_cap.capabilities;
 		if (pmu->pmu_type & hybrid_small_tiny) {
 			pmu->intel_cap.perf_metrics = 0;
-			pmu->intel_cap.pebs_output_pt_available = 1;
 			pmu->mid_ack = true;
 		} else if (pmu->pmu_type & hybrid_big) {
 			pmu->intel_cap.perf_metrics = 1;
-			pmu->intel_cap.pebs_output_pt_available = 0;
 			pmu->late_ack = true;
 		}
 	}
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index ba74e11..c2e2eae 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -2578,7 +2578,15 @@ void __init intel_ds_init(void)
 			}
 			pr_cont("PEBS fmt4%c%s, ", pebs_type, pebs_qual);
 
-			if (!is_hybrid() && x86_pmu.intel_cap.pebs_output_pt_available) {
+			/*
+			 * The PEBS-via-PT is not supported on hybrid platforms,
+			 * because not all CPUs of a hybrid machine support it.
+			 * The global x86_pmu.intel_cap, which only contains the
+			 * common capabilities, is used to check the availability
+			 * of the feature. The per-PMU pebs_output_pt_available
+			 * in a hybrid machine should be ignored.
+			 */
+			if (x86_pmu.intel_cap.pebs_output_pt_available) {
 				pr_cont("PEBS-via-PT, ");
 				x86_get_pmu(smp_processor_id())->capabilities |= PERF_PMU_CAP_AUX_OUTPUT;
 			}