[PATCH 16/19] perf: Introduce positive capability for sampling

From: Robin Murphy <robin.murphy@arm.com>
Date: 2025-08-13 17:02:37
Also in: amd-gfx, dmaengine, dri-devel, imx, intel-gfx, intel-xe, linux-alpha, linux-amlogic, linux-arm-kernel, linux-arm-msm, linux-cxl, linux-fpga, linux-iommu, linux-mips, linux-perf-users, linux-pm, linux-riscv, linux-rockchip, linux-s390, linux-sh, lkml, loongarch, sparclinux
Subsystem: alpha port, arm pmu profiling and debugging, c-sky architecture, linux for powerpc (32-bit and 64-bit), loongarch, mips, performance events subsystem, risc-v pmu drivers, s390 architecture, sparc + ultrasparc (sparc/sparc64), synopsys arc architecture, tensilica xtensa port (xtensa), the rest, x86 architecture (32-bit and 64-bit) · Maintainers: Richard Henderson, Matt Turner, Magnus Lindholm, Will Deacon, Mark Rutland, Guo Ren, Madhavan Srinivasan, Michael Ellerman, Huacai Chen, Thomas Bogendoerfer, Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo, Namhyung Kim, Atish Patra, Heiko Carstens, Vasily Gorbik, Alexander Gordeev, "David S. Miller", Andreas Larsson, Vineet Gupta, Chris Zankel, Max Filippov, Linus Torvalds, Thomas Gleixner, Borislav Petkov, Dave Hansen

Sampling is inherently a feature for CPU PMUs, given that the thing
to be sampled is a CPU context. These days, we have many more
uncore/system PMUs than CPU PMUs, so it no longer makes much sense to
assume sampling support by default and force the ever-growing majority
of drivers to opt out of it (or erroneously fail to). Instead, let's
introduce a positive opt-in capability that's more obvious and easier to
maintain.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 arch/alpha/kernel/perf_event.c       |  3 ++-
 arch/arc/kernel/perf_event.c         |  2 ++
 arch/csky/kernel/perf_event.c        |  2 ++
 arch/loongarch/kernel/perf_event.c   |  1 +
 arch/mips/kernel/perf_event_mipsxx.c |  1 +
 arch/powerpc/perf/core-book3s.c      |  1 +
 arch/powerpc/perf/core-fsl-emb.c     |  1 +
 arch/powerpc/perf/imc-pmu.c          |  1 +
 arch/s390/kernel/perf_cpum_cf.c      |  1 +
 arch/s390/kernel/perf_cpum_sf.c      |  2 ++
 arch/s390/kernel/perf_pai_crypto.c   |  1 +
 arch/s390/kernel/perf_pai_ext.c      |  1 +
 arch/sparc/kernel/perf_event.c       |  1 +
 arch/x86/events/amd/ibs.c            |  2 ++
 arch/x86/events/core.c               |  4 +++-
 arch/xtensa/kernel/perf_event.c      |  1 +
 drivers/perf/arm_pmu.c               |  3 ++-
 drivers/perf/arm_pmu_platform.c      |  1 +
 drivers/perf/arm_spe_pmu.c           |  3 ++-
 drivers/perf/riscv_pmu_sbi.c         |  2 ++
 include/linux/perf_event.h           |  3 ++-
 kernel/events/core.c                 | 20 +++++++++++---------
 kernel/events/hw_breakpoint.c        |  1 +
 23 files changed, 44 insertions(+), 14 deletions(-)

diff --git a/arch/alpha/kernel/perf_event.c b/arch/alpha/kernel/perf_event.c
index 8557165e64c0..4de1802d249f 100644
--- a/arch/alpha/kernel/perf_event.c
+++ b/arch/alpha/kernel/perf_event.c

@@ -761,7 +761,8 @@ static struct pmu pmu = {
 	.start		= alpha_pmu_start,
 	.stop		= alpha_pmu_stop,
 	.read		= alpha_pmu_read,
-	.capabilities	= PERF_PMU_CAP_NO_EXCLUDE,
+	.capabilities	= PERF_PMU_CAP_SAMPLING |
+			  PERF_PMU_CAP_NO_EXCLUDE,
 };

diff --git a/arch/arc/kernel/perf_event.c b/arch/arc/kernel/perf_event.c
index ed6d4f0cd621..1b99b0215027 100644
--- a/arch/arc/kernel/perf_event.c
+++ b/arch/arc/kernel/perf_event.c

@@ -818,6 +818,8 @@ static int arc_pmu_device_probe(struct platform_device *pdev)
 
 	if (irq == -1)
 		arc_pmu->pmu.capabilities |= PERF_PMU_CAP_NO_INTERRUPT;
+	else
+		arc_pmu->pmu.capabilities |= PERF_PMU_CAP_SAMPLING;
 
 	/*
 	 * perf parser doesn't really like '-' symbol in events name, so let's

diff --git a/arch/csky/kernel/perf_event.c b/arch/csky/kernel/perf_event.c
index e0a36acd265b..c5ba6e235a6f 100644
--- a/arch/csky/kernel/perf_event.c
+++ b/arch/csky/kernel/perf_event.c

@@ -1204,6 +1204,7 @@ int init_hw_perf_events(void)
 	}
 
 	csky_pmu.pmu = (struct pmu) {
+		.capabilities	= PERF_PMU_CAP_SAMPLING,
 		.pmu_enable	= csky_pmu_enable,
 		.pmu_disable	= csky_pmu_disable,
 		.event_init	= csky_pmu_event_init,

@@ -1314,6 +1315,7 @@ int csky_pmu_device_probe(struct platform_device *pdev,
 
 	ret = csky_pmu_request_irq(csky_pmu_handle_irq);
 	if (ret) {
+		csky_pmu.pmu.capabilities &= ~PERF_PMU_CAP_SAMPLING;
 		csky_pmu.pmu.capabilities |= PERF_PMU_CAP_NO_INTERRUPT;
 		pr_notice("[perf] PMU request irq fail!\n");
 	}

diff --git a/arch/loongarch/kernel/perf_event.c b/arch/loongarch/kernel/perf_event.c
index 8ad098703488..341b17bedd0e 100644
--- a/arch/loongarch/kernel/perf_event.c
+++ b/arch/loongarch/kernel/perf_event.c

@@ -571,6 +571,7 @@ static int loongarch_pmu_event_init(struct perf_event *event)
 }
 
 static struct pmu pmu = {
+	.capabilities	= PERF_PMU_CAP_SAMPLING,
 	.pmu_enable	= loongarch_pmu_enable,
 	.pmu_disable	= loongarch_pmu_disable,
 	.event_init	= loongarch_pmu_event_init,

diff --git a/arch/mips/kernel/perf_event_mipsxx.c b/arch/mips/kernel/perf_event_mipsxx.c
index 196a070349b0..4c5d64d1158e 100644
--- a/arch/mips/kernel/perf_event_mipsxx.c
+++ b/arch/mips/kernel/perf_event_mipsxx.c

@@ -687,6 +687,7 @@ static int mipspmu_event_init(struct perf_event *event)
 }
 
 static struct pmu pmu = {
+	.capabilities	= PERF_PMU_CAP_SAMPLING,
 	.pmu_enable	= mipspmu_enable,
 	.pmu_disable	= mipspmu_disable,
 	.event_init	= mipspmu_event_init,

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index d67f7d511f13..cfe7d3c120e1 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c

@@ -2207,6 +2207,7 @@ ssize_t power_events_sysfs_show(struct device *dev,
 }
 
 static struct pmu power_pmu = {
+	.capabilities	= PERF_PMU_CAP_SAMPLING,
 	.pmu_enable	= power_pmu_enable,
 	.pmu_disable	= power_pmu_disable,
 	.event_init	= power_pmu_event_init,

diff --git a/arch/powerpc/perf/core-fsl-emb.c b/arch/powerpc/perf/core-fsl-emb.c
index 509932b91b75..62038ff3663f 100644
--- a/arch/powerpc/perf/core-fsl-emb.c
+++ b/arch/powerpc/perf/core-fsl-emb.c

@@ -570,6 +570,7 @@ static int fsl_emb_pmu_event_init(struct perf_event *event)
 }
 
 static struct pmu fsl_emb_pmu = {
+	.capabilities	= PERF_PMU_CAP_SAMPLING,
 	.pmu_enable	= fsl_emb_pmu_enable,
 	.pmu_disable	= fsl_emb_pmu_disable,
 	.event_init	= fsl_emb_pmu_event_init,

diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
index 8664a7d297ad..f352dda3baf9 100644
--- a/arch/powerpc/perf/imc-pmu.c
+++ b/arch/powerpc/perf/imc-pmu.c

@@ -1507,6 +1507,7 @@ static int update_pmu_ops(struct imc_pmu *pmu)
 		pmu->pmu.commit_txn = thread_imc_pmu_commit_txn;
 		break;
 	case IMC_DOMAIN_TRACE:
+		pmu->pmu.capabilities |= PERF_PMU_CAP_SAMPLING;
 		pmu->pmu.event_init = trace_imc_event_init;
 		pmu->pmu.add = trace_imc_event_add;
 		pmu->pmu.del = trace_imc_event_del;

diff --git a/arch/s390/kernel/perf_cpum_cf.c b/arch/s390/kernel/perf_cpum_cf.c
index 4d09954ebf49..7d10842d54f0 100644
--- a/arch/s390/kernel/perf_cpum_cf.c
+++ b/arch/s390/kernel/perf_cpum_cf.c

@@ -1861,6 +1861,7 @@ static const struct attribute_group *cfdiag_attr_groups[] = {
  */
 static struct pmu cf_diag = {
 	.task_ctx_nr  = perf_sw_context,
+	.capabilities = PERF_PMU_CAP_SAMPLING,
 	.event_init   = cfdiag_event_init,
 	.pmu_enable   = cpumf_pmu_enable,
 	.pmu_disable  = cpumf_pmu_disable,

diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c
index f432869f8921..3d2c400f0aaa 100644
--- a/arch/s390/kernel/perf_cpum_sf.c
+++ b/arch/s390/kernel/perf_cpum_sf.c

@@ -1892,6 +1892,8 @@ static const struct attribute_group *cpumsf_pmu_attr_groups[] = {
 };
 
 static struct pmu cpumf_sampling = {
+	.capabilities = PERF_PMU_CAP_SAMPLING,
+
 	.pmu_enable   = cpumsf_pmu_enable,
 	.pmu_disable  = cpumsf_pmu_disable,

diff --git a/arch/s390/kernel/perf_pai_crypto.c b/arch/s390/kernel/perf_pai_crypto.c
index f373a1009c45..a64b6b056a21 100644
--- a/arch/s390/kernel/perf_pai_crypto.c
+++ b/arch/s390/kernel/perf_pai_crypto.c

@@ -569,6 +569,7 @@ static const struct attribute_group *paicrypt_attr_groups[] = {
 /* Performance monitoring unit for mapped counters */
 static struct pmu paicrypt = {
 	.task_ctx_nr  = perf_hw_context,
+	.capabilities = PERF_PMU_CAP_SAMPLING,
 	.event_init   = paicrypt_event_init,
 	.add	      = paicrypt_add,
 	.del	      = paicrypt_del,

diff --git a/arch/s390/kernel/perf_pai_ext.c b/arch/s390/kernel/perf_pai_ext.c
index d827473e7f87..1261f80c6d52 100644
--- a/arch/s390/kernel/perf_pai_ext.c
+++ b/arch/s390/kernel/perf_pai_ext.c

@@ -595,6 +595,7 @@ static const struct attribute_group *paiext_attr_groups[] = {
 /* Performance monitoring unit for mapped counters */
 static struct pmu paiext = {
 	.task_ctx_nr  = perf_hw_context,
+	.capabilities = PERF_PMU_CAP_SAMPLING,
 	.event_init   = paiext_event_init,
 	.add	      = paiext_add,
 	.del	      = paiext_del,

diff --git a/arch/sparc/kernel/perf_event.c b/arch/sparc/kernel/perf_event.c
index 706127749c66..6ecea8e7b592 100644
--- a/arch/sparc/kernel/perf_event.c
+++ b/arch/sparc/kernel/perf_event.c

@@ -1573,6 +1573,7 @@ static int sparc_pmu_commit_txn(struct pmu *pmu)
 }
 
 static struct pmu pmu = {
+	.capabilities	= PERF_PMU_CAP_SAMPLING,
 	.pmu_enable	= sparc_pmu_enable,
 	.pmu_disable	= sparc_pmu_disable,
 	.event_init	= sparc_pmu_event_init,

diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index 95de309fc7d5..ed07d80b6fe0 100644
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c

@@ -768,6 +768,7 @@ static struct perf_ibs perf_ibs_fetch = {
 	.pmu = {
 		.task_ctx_nr	= perf_hw_context,
 
+		.capabilities	= PERF_PMU_CAP_SAMPLING,
 		.event_init	= perf_ibs_init,
 		.add		= perf_ibs_add,
 		.del		= perf_ibs_del,

@@ -793,6 +794,7 @@ static struct perf_ibs perf_ibs_op = {
 	.pmu = {
 		.task_ctx_nr	= perf_hw_context,
 
+		.capabilities	= PERF_PMU_CAP_SAMPLING,
 		.event_init	= perf_ibs_init,
 		.add		= perf_ibs_add,
 		.del		= perf_ibs_del,

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index eca5bb49aa85..72a4c43951ee 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c

@@ -1837,7 +1837,7 @@ static void __init pmu_check_apic(void)
 	 * sample via a hrtimer based software event):
 	 */
 	pmu.capabilities |= PERF_PMU_CAP_NO_INTERRUPT;
-
+	pmu.capabilities &= ~PERF_PMU_CAP_SAMPLING;
 }
 
 static struct attribute_group x86_pmu_format_group __ro_after_init = {

@@ -2698,6 +2698,8 @@ static bool x86_pmu_filter(struct pmu *pmu, int cpu)
 }
 
 static struct pmu pmu = {
+	.capabilities		= PERF_PMU_CAP_SAMPLING,
+
 	.pmu_enable		= x86_pmu_enable,
 	.pmu_disable		= x86_pmu_disable,

diff --git a/arch/xtensa/kernel/perf_event.c b/arch/xtensa/kernel/perf_event.c
index 223f1d452310..b03a2feb0f92 100644
--- a/arch/xtensa/kernel/perf_event.c
+++ b/arch/xtensa/kernel/perf_event.c

@@ -397,6 +397,7 @@ irqreturn_t xtensa_pmu_irq_handler(int irq, void *dev_id)
 }
 
 static struct pmu xtensa_pmu = {
+	.capabilities = PERF_PMU_CAP_SAMPLING,
 	.pmu_enable = xtensa_pmu_enable,
 	.pmu_disable = xtensa_pmu_disable,
 	.event_init = xtensa_pmu_event_init,

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index 2c1af3a0207c..72d8f38d0aa5 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c

@@ -876,7 +876,8 @@ struct arm_pmu *armpmu_alloc(void)
 		 * PERF_TYPE_HARDWARE and PERF_TYPE_HW_CACHE events on a
 		 * specific PMU.
 		 */
-		.capabilities	= PERF_PMU_CAP_EXTENDED_REGS |
+		.capabilities	= PERF_PMU_CAP_SAMPLING |
+				  PERF_PMU_CAP_EXTENDED_REGS |
 				  PERF_PMU_CAP_EXTENDED_HW_TYPE,
 	};

diff --git a/drivers/perf/arm_pmu_platform.c b/drivers/perf/arm_pmu_platform.c
index 118170a5cede..ab7a802cd0d6 100644
--- a/drivers/perf/arm_pmu_platform.c
+++ b/drivers/perf/arm_pmu_platform.c

@@ -109,6 +109,7 @@ static int pmu_parse_irqs(struct arm_pmu *pmu)
 	 */
 	if (num_irqs == 0) {
 		dev_warn(dev, "no irqs for PMU, sampling events not supported\n");
+		pmu->pmu.capabilities &= ~PERF_PMU_CAP_SAMPLING;
 		pmu->pmu.capabilities |= PERF_PMU_CAP_NO_INTERRUPT;
 		cpumask_setall(&pmu->supported_cpus);
 		return 0;

diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
index 369e77ad5f13..dbd52851f5c6 100644
--- a/drivers/perf/arm_spe_pmu.c
+++ b/drivers/perf/arm_spe_pmu.c

@@ -955,7 +955,8 @@ static int arm_spe_pmu_perf_init(struct arm_spe_pmu *spe_pmu)
 	spe_pmu->pmu = (struct pmu) {
 		.module = THIS_MODULE,
 		.parent		= &spe_pmu->pdev->dev,
-		.capabilities	= PERF_PMU_CAP_EXCLUSIVE | PERF_PMU_CAP_ITRACE,
+		.capabilities	= PERF_PMU_CAP_SAMPLING |
+				  PERF_PMU_CAP_EXCLUSIVE | PERF_PMU_CAP_ITRACE,
 		.attr_groups	= arm_spe_pmu_attr_groups,
 		/*
 		 * We hitch a ride on the software context here, so that

diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
index 698de8ddf895..d185ea8c47ba 100644
--- a/drivers/perf/riscv_pmu_sbi.c
+++ b/drivers/perf/riscv_pmu_sbi.c

@@ -1361,6 +1361,8 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
 		pr_info("Perf sampling/filtering is not supported as sscof extension is not available\n");
 		pmu->pmu.capabilities |= PERF_PMU_CAP_NO_INTERRUPT;
 		pmu->pmu.capabilities |= PERF_PMU_CAP_NO_EXCLUDE;
+	} else {
+		pmu->pmu.capabilities |= PERF_PMU_CAP_SAMPLING;
 	}
 
 	pmu->pmu.attr_groups = riscv_pmu_attr_groups;

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 4d439c24c901..bf2cfbeabba2 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h

@@ -294,7 +294,7 @@ struct perf_event_pmu_context;
 /**
  * pmu::capabilities flags
  */
-#define PERF_PMU_CAP_NO_INTERRUPT	0x0001
+#define PERF_PMU_CAP_SAMPLING		0x0001
 #define PERF_PMU_CAP_NO_NMI		0x0002
 #define PERF_PMU_CAP_AUX_NO_SG		0x0004
 #define PERF_PMU_CAP_EXTENDED_REGS	0x0008

@@ -305,6 +305,7 @@ struct perf_event_pmu_context;
 #define PERF_PMU_CAP_EXTENDED_HW_TYPE	0x0100
 #define PERF_PMU_CAP_AUX_PAUSE		0x0200
 #define PERF_PMU_CAP_AUX_PREFER_LARGE	0x0400
+#define PERF_PMU_CAP_NO_INTERRUPT	0x0800
 
 /**
  * pmu::scope

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 8060c2857bb2..71b2a6730705 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c

@@ -4359,7 +4359,7 @@ perf_adjust_freq_unthr_context(struct perf_event_context *ctx, bool unthrottle)
 			continue;
 		if (!perf_pmu_ctx_is_active(pmu_ctx))
 			continue;
-		if (pmu_ctx->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT)
+		if (!(pmu_ctx->pmu->capabilities & PERF_PMU_CAP_SAMPLING))
 			continue;
 
 		perf_pmu_disable(pmu_ctx->pmu);

@@ -10819,7 +10819,7 @@ static int perf_swevent_init(struct perf_event *event)
 static struct pmu perf_swevent = {
 	.task_ctx_nr	= perf_sw_context,
 
-	.capabilities	= PERF_PMU_CAP_NO_NMI,
+	.capabilities	= PERF_PMU_CAP_SAMPLING | PERF_PMU_CAP_NO_NMI,
 
 	.event_init	= perf_swevent_init,
 	.add		= perf_swevent_add,

@@ -10861,6 +10861,7 @@ static int perf_tp_event_init(struct perf_event *event)
 static struct pmu perf_tracepoint = {
 	.task_ctx_nr	= perf_sw_context,
 
+	.capabilities	= PERF_PMU_CAP_SAMPLING,
 	.event_init	= perf_tp_event_init,
 	.add		= perf_trace_add,
 	.del		= perf_trace_del,

@@ -11066,6 +11067,7 @@ static struct pmu perf_kprobe = {
 	.stop		= perf_swevent_stop,
 	.read		= perf_swevent_read,
 	.attr_groups	= kprobe_attr_groups,
+	.capabilities	= PERF_PMU_CAP_SAMPLING,
 };
 
 static int perf_kprobe_event_init(struct perf_event *event)

@@ -11125,6 +11127,7 @@ static struct pmu perf_uprobe = {
 	.stop		= perf_swevent_stop,
 	.read		= perf_swevent_read,
 	.attr_groups	= uprobe_attr_groups,
+	.capabilities	= PERF_PMU_CAP_SAMPLING,
 };
 
 static int perf_uprobe_event_init(struct perf_event *event)

@@ -11899,7 +11902,7 @@ static int cpu_clock_event_init(struct perf_event *event)
 static struct pmu perf_cpu_clock = {
 	.task_ctx_nr	= perf_sw_context,
 
-	.capabilities	= PERF_PMU_CAP_NO_NMI,
+	.capabilities	= PERF_PMU_CAP_SAMPLING | PERF_PMU_CAP_NO_NMI,
 	.dev		= PMU_NULL_DEV,
 
 	.event_init	= cpu_clock_event_init,

@@ -11982,7 +11985,7 @@ static int task_clock_event_init(struct perf_event *event)
 static struct pmu perf_task_clock = {
 	.task_ctx_nr	= perf_sw_context,
 
-	.capabilities	= PERF_PMU_CAP_NO_NMI,
+	.capabilities	= PERF_PMU_CAP_SAMPLING | PERF_PMU_CAP_NO_NMI,
 	.dev		= PMU_NULL_DEV,
 
 	.event_init	= task_clock_event_init,

@@ -13476,11 +13479,10 @@ SYSCALL_DEFINE5(perf_event_open,
 		goto err_task;
 	}
 
-	if (is_sampling_event(event)) {
-		if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) {
-			err = -EOPNOTSUPP;
-			goto err_alloc;
-		}
+	if (is_sampling_event(event) &&
+	    !(event->pmu->capabilities & PERF_PMU_CAP_SAMPLING)) {
+		err = -EOPNOTSUPP;
+		goto err_alloc;
 	}
 
 	/*

diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index 8ec2cb688903..604be7d7aecf 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c

@@ -996,6 +996,7 @@ static void hw_breakpoint_stop(struct perf_event *bp, int flags)
 static struct pmu perf_breakpoint = {
 	.task_ctx_nr	= perf_sw_context, /* could eventually get its own */
 
+	.capabilities	= PERF_PMU_CAP_SAMPLING,
 	.event_init	= hw_breakpoint_event_init,
 	.add		= hw_breakpoint_add,
 	.del		= hw_breakpoint_del,

-- 
2.39.2.101.g768bb238c484.dirty

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