* [RFC PATCH 1/7] mm/damon/perf: add observability framework with tracepoints and CONFIG switch
2026-08-18 6:10 [RFC PATCH 0/7] mm/damon/perf: observability framework for hardware-sampled access reports Kunwu Chan
@ 2026-08-18 6:10 ` Kunwu Chan
2026-08-18 6:10 ` [RFC PATCH 2/7] mm/damon/perf: implement observe API and per-CPU statistics engine Kunwu Chan
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: Kunwu Chan @ 2026-08-18 6:10 UTC (permalink / raw)
To: sj, akpm
Cc: damon, linux-mm, linux-kernel, linux-trace-kernel,
linux-kselftest, rostedt, mhiramat, mathieu.desnoyers, shuah,
lianux.mm, Kunwu Chan
From: Kunwu Chan <kunwu.chan@gmail.com>
Add the observe framework headers together with the compile-time switch
that gates the whole feature: the three DAMON perf tracepoints this
series adds (guarded with CONFIG_DAMON_PERF_OBSERVE so they are not
registered when the switch is off; damon_perf_ring_overflow is provided
by the base series), the observe API declarations with static-inline
no-ops for disabled builds, the access-report contract (miss-reason
enum, report-source enum, report source field, per-event cpu_state
member), and the Kconfig and Makefile wiring.
The sample tracepoint carries what the PMU actually populated
(data->sample_flags), what was requested (perf_event->attr.
sample_type), and the execution context (process/softirq/hardirq/NMI)
in a single line, so PMU support gaps and context expectations (e.g.
IBS overflow in NMI, SPE AUX drain in process context) are verifiable
at a glance.
Every following commit in this series builds with CONFIG_DAMON_PERF_OBSERVE
both enabled and disabled.
Co-developed-by: Lian Wang <lianux.mm@gmail.com>
Signed-off-by: Lian Wang <lianux.mm@gmail.com>
Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
---
include/linux/damon.h | 44 +++++++
include/trace/events/damon.h | 120 ++++++++++++++++++
mm/damon/Kconfig | 17 +++
mm/damon/Makefile | 1 +
mm/damon/perf/Makefile | 3 +
mm/damon/perf/perf.h | 228 +++++++++++++++++++++++++++++++++++
6 files changed, 413 insertions(+)
create mode 100644 mm/damon/perf/Makefile
create mode 100644 mm/damon/perf/perf.h
diff --git a/include/linux/damon.h b/include/linux/damon.h
index 11f1c1071b9b..c191c065b0e4 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -116,6 +116,19 @@ struct damon_target {
bool obsolete;
};
+/**
+ * enum damon_report_source - Tells which subsystem produced an access report.
+ *
+ * Ring and matching counters aggregate all sources; this enum lets callers
+ * tag reports so that tracepoints and future per-source breakdowns can
+ * distinguish NMI overflow-handler samples from
+ * page-fault hints.
+ */
+enum damon_report_source {
+ DAMON_REPORT_SRC_PERF_OVERFLOW = 0, /* overflow_handler (IBS, PEBS) */
+ DAMON_REPORT_SRC_PAGE_FAULT, /* damon_report_page_fault() */
+};
+
/**
* struct damon_access_report - Represent single access report information.
* @paddr: Start physical address of the accessed address range.
@@ -125,6 +138,8 @@ struct damon_target {
* @tid: The task id of the task that made the access.
* @tgid: Thread group id of the task that made the access.
* @is_write: Whether the access is write.
+ * @source: Which subsystem produced this report
+ * (enum damon_report_source).
*
* Any DAMON API callers that notified access events can report the information
* to DAMON using damon_report_access(). This struct contains the reporting
@@ -138,10 +153,28 @@ struct damon_access_report {
pid_t tid;
pid_t tgid;
bool is_write;
+#ifdef CONFIG_DAMON_PERF_OBSERVE
+ int source;
+#endif /* CONFIG_DAMON_PERF_OBSERVE */
/* private: */
unsigned long report_jiffies; /* when this report is made */
};
+/*
+ * Reason codes for trace_damon_perf_report_missed.
+ *
+ * DAMON_REPORT_MISS_TGID: tgid mismatch (pid-based monitoring,
+ * missed at drain-loop level before the
+ * per-target iteration).
+ * DAMON_REPORT_MISS_NOREGION: binary search found no containing region.
+ * DAMON_REPORT_MISS_BOUNDARY: address + size straddles region boundary.
+ */
+enum damon_report_miss_reason {
+ DAMON_REPORT_MISS_TGID = 1,
+ DAMON_REPORT_MISS_NOREGION = 2,
+ DAMON_REPORT_MISS_BOUNDARY = 3,
+};
+
/**
* enum damos_action - Represents an action of a Data Access Monitoring-based
* Operation Scheme.
@@ -1027,6 +1060,17 @@ struct damon_perf_event {
struct hlist_node hlist_node;
bool init_complete;
bool any_cpu_failed;
+#ifdef CONFIG_DAMON_PERF_OBSERVE
+ /*
+ * Per-CPU lifecycle state (enum damon_perf_event_state).
+ * Allocated lazily on the first observe_event_created(),
+ * freed on observe_event_destroyed(). Each event tracks
+ * its own progression through CREATED->BOUND->ENABLED,
+ * so destroying one event does not overwrite another"s
+ * state on the same CPU.
+ */
+ int __percpu *cpu_state;
+#endif /* CONFIG_DAMON_PERF_OBSERVE */
struct damon_ctx *ctx;
};
diff --git a/include/trace/events/damon.h b/include/trace/events/damon.h
index 877627c9a1a1..c87fbeefb85a 100644
--- a/include/trace/events/damon.h
+++ b/include/trace/events/damon.h
@@ -91,6 +91,126 @@ TRACE_EVENT(damon_perf_ring_overflow,
TP_printk("cpu=%d", __entry->cpu)
);
+#ifdef CONFIG_DAMON_PERF_OBSERVE
+/*
+ * Fires from NMI overflow handlers on every hardware sample received,
+ * before any DAMON-side filtering. Records the raw address, full
+ * data_src (mem_op, mem_lvl, mem_snoop, mem_remote), period, and a
+ * reason code so userspace can distinguish:
+ *
+ * 0 = valid sample, queued to per-CPU ring
+ * 1 = data == NULL
+ * 2 = addr == 0 (PMU did not populate data->addr)
+ * 3 = kernel address (vaddr handler: addr >= TASK_SIZE)
+ * 4 = phys_addr not valid (paddr handler: !PERF_SAMPLE_PHYS_ADDR)
+ *
+ * data_src carries the raw union perf_mem_data_src value; use
+ * perf_mem__xxx macros to decode.
+ *
+ * sample_flags is what the PMU *actually* populated (from
+ * data->sample_flags); sample_type is what was *requested* (from
+ * perf_event->attr.sample_type). Comparing them immediately
+ * reveals whether the PMU is providing the fields DAMON asked for
+ * — e.g. sample_type has PERF_SAMPLE_PHYS_ADDR but sample_flags
+ * does not → the PMU does not support physical-address sampling.
+ */
+TRACE_EVENT(damon_perf_sample,
+
+ TP_PROTO(unsigned long addr, u64 data_src, u64 period, int cpu,
+ u8 reason, u64 sample_flags, u64 sample_type,
+ u8 context),
+
+ TP_ARGS(addr, data_src, period, cpu, reason, sample_flags,
+ sample_type, context),
+
+ TP_STRUCT__entry(
+ __field(unsigned long, addr)
+ __field(u64, data_src)
+ __field(u64, period)
+ __field(int, cpu)
+ __field(u8, reason)
+ __field(u64, sample_flags)
+ __field(u64, sample_type)
+ __field(u8, context)
+ ),
+
+ TP_fast_assign(
+ __entry->addr = addr;
+ __entry->data_src = data_src;
+ __entry->period = period;
+ __entry->cpu = cpu;
+ __entry->reason = reason;
+ __entry->sample_flags = sample_flags;
+ __entry->sample_type = sample_type;
+ __entry->context = context;
+ ),
+
+ TP_printk("addr=0x%lx data_src=0x%llx period=%llu cpu=%d reason=%u context=%u sample_flags=0x%llx sample_type=0x%llx",
+ __entry->addr, __entry->data_src, __entry->period,
+ __entry->cpu, __entry->reason, __entry->context,
+ __entry->sample_flags, __entry->sample_type)
+);
+
+/*
+ * Fires when a report survived all ring/drain checks but could not be
+ * applied to any DAMON region. Reasons correspond to
+ * enum damon_report_miss_reason:
+ *
+ * DAMON_REPORT_MISS_TGID (1): no target matched the report's tgid
+ * DAMON_REPORT_MISS_NOREGION (2): binary search found no containing region
+ * DAMON_REPORT_MISS_BOUNDARY (3): address + size straddles region boundary
+ *
+ * Note: tgid mismatches are now resolved in the drain loop *before*
+ * iterating targets, so there is at most one trace hit per report
+ * (rather than one per non-matching target as in earlier revisions).
+ */
+TRACE_EVENT(damon_perf_report_missed,
+
+ TP_PROTO(unsigned long addr, int cpu, int reason),
+
+ TP_ARGS(addr, cpu, reason),
+
+ TP_STRUCT__entry(
+ __field(unsigned long, addr)
+ __field(int, cpu)
+ __field(int, reason)
+ ),
+
+ TP_fast_assign(
+ __entry->addr = addr;
+ __entry->cpu = cpu;
+ __entry->reason = reason;
+ ),
+
+ TP_printk("addr=0x%lx cpu=%d reason=%d", __entry->addr,
+ __entry->cpu, __entry->reason)
+);
+
+/*
+ * Per-tick drain summary. Fires from kdamond after draining the per-CPU
+ * SPSC ring, so users can observe total vs matched without polling dmesg
+ * or correlating individual miss tracepoints.
+ */
+TRACE_EVENT(damon_perf_drain,
+
+ TP_PROTO(unsigned int total, unsigned int matched),
+
+ TP_ARGS(total, matched),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, total)
+ __field(unsigned int, matched)
+ ),
+
+ TP_fast_assign(
+ __entry->total = total;
+ __entry->matched = matched;
+ ),
+
+ TP_printk("total=%u matched=%u", __entry->total, __entry->matched)
+);
+#endif /* CONFIG_DAMON_PERF_OBSERVE */
+
/* Per-tick DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP goal evaluation. */
TRACE_EVENT(damos_node_eligible_mem_bp,
diff --git a/mm/damon/Kconfig b/mm/damon/Kconfig
index ad629f0f31d8..9f811510760f 100644
--- a/mm/damon/Kconfig
+++ b/mm/damon/Kconfig
@@ -131,4 +131,21 @@ config DAMON_ACMA
min/max memory for the system and maximum memory pressure stall time
ratio.
+config DAMON_PERF_OBSERVE
+ bool "DAMON perf event observability framework"
+ depends on DAMON
+ depends on PERF_EVENTS
+ depends on DEBUG_FS
+ default n
+ help
+ Enable per-CPU pipeline counters, tracepoints, and a
+ debug-only debugfs perf_stats file for DAMON
+ hardware-sampled access reports. The debugfs format is
+ unstable and must not be used by scripts; counters and
+ tracepoints are the diagnostic interface.
+
+ When disabled, all observe functions are compiled to
+ static-inline no-ops with zero runtime overhead.
+
+ If unsure, say N.
endmenu
diff --git a/mm/damon/Makefile b/mm/damon/Makefile
index 22494754f41e..04da39a9f56c 100644
--- a/mm/damon/Makefile
+++ b/mm/damon/Makefile
@@ -9,3 +9,4 @@ obj-$(CONFIG_DAMON_RECLAIM) += modules-common.o reclaim.o
obj-$(CONFIG_DAMON_LRU_SORT) += modules-common.o lru_sort.o
obj-$(CONFIG_DAMON_STAT) += modules-common.o stat.o
obj-$(CONFIG_DAMON_ACMA) += modules-common.o acma.o
+obj-$(CONFIG_DAMON) += perf/
diff --git a/mm/damon/perf/Makefile b/mm/damon/perf/Makefile
new file mode 100644
index 000000000000..cc0d4f1d1d28
--- /dev/null
+++ b/mm/damon/perf/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# Observability: per-CPU counters, tracepoints, debugfs perf_stats
diff --git a/mm/damon/perf/perf.h b/mm/damon/perf/perf.h
new file mode 100644
index 000000000000..78e23d436336
--- /dev/null
+++ b/mm/damon/perf/perf.h
@@ -0,0 +1,228 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * DAMON Hardware-sampled Access Report Observability Framework
+ *
+ * Single entry-point for all hardware sampling backends (ARM SPE,
+ * AMD IBS, Intel PEBS, …). Every event, sample, ring operation,
+ * match decision, and region update flows through the
+ * damon_perf_observe_*() API, which fans out to per-CPU counters
+ * and tracepoints. When CONFIG_DAMON_PERF_OBSERVE=n, everything
+ * compiles to static-inline no-ops.
+ *
+ * Author: Kunwu Chan <kunwu.chan@gmail.com>
+ */
+
+#ifndef _DAMON_PERF_H
+#define _DAMON_PERF_H
+
+struct perf_event;
+#include <linux/types.h>
+
+struct damon_perf_event;
+
+/*
+ * Per-event state machine
+ *
+ * Each per-CPU damon_perf_event transitions through these states.
+ * State is tracked in a per-CPU integer (damon_perf_cpu_state).
+ */
+enum damon_perf_event_state {
+ DAMON_PERF_STATE_UNINIT = 0,
+ DAMON_PERF_STATE_CREATED, /* struct allocated, cpuhp registered */
+ DAMON_PERF_STATE_BOUND, /* perf_event_create_kernel_counter() ok */
+ DAMON_PERF_STATE_ENABLED, /* perf_event_enable() called */
+ DAMON_PERF_STATE_RUNNING, /* first overflow callback received */
+ DAMON_PERF_STATE_ERROR, /* unrecoverable failure */
+};
+
+/*
+ * Per-CPU statistics
+ *
+ * All counters are monotonic, best-effort reads. Userspace computes
+ * deltas between snapshots. Stored per-CPU so the NMI fast path uses
+ * this_cpu_inc() with no locking. Counter values are raw facts:
+ * interpretation (thresholds, verdicts) belongs in userspace.
+ *
+ * The kernel provides tracepoints under events/damon/ for structured,
+ * stable diagnostics. The debugfs perf_stats file is DEBUG ONLY and
+ * its format may change without notice.
+ */
+struct damon_perf_stats {
+ /* Per-CPU event state (enum damon_perf_event_state) */
+ int cpu_state;
+
+ /* Sampling pipeline */
+ u64 callback;
+ u64 sample_valid;
+ u64 sample_null;
+ u64 sample_addr_zero;
+ u64 sample_kernel;
+ u64 sample_invalid_phys;
+
+ /* Ring */
+ u64 enqueue;
+ u64 dequeue;
+ u64 overflow;
+ u64 ring_peak;
+
+ /* Matching */
+ u64 match;
+ u64 miss_tgid;
+ u64 miss_region;
+ u64 miss_boundary;
+ u64 update;
+};
+
+#ifdef CONFIG_DAMON_PERF_OBSERVE
+
+/*
+ * damon_perf_observe_*() — Unified Observability API
+ *
+ * These are the ONLY hooks that hardware-sampling backends should
+ * call. They are split into NMI-safe (sampling, ring-enqueue) and
+ * process-context (event lifecycle, drain, matching, update) groups.
+ *
+ * Counters always increment when CONFIG_DAMON_PERF_OBSERVE=y.
+ * Tracepoints are guarded by trace_*_enabled() and incur zero
+ * overhead when ftrace is not attached.
+ */
+
+/* Event lifecycle — process context (kdamond / cpuhp callbacks) */
+void damon_perf_observe_event_created(struct damon_perf_event *event,
+ int cpu);
+void damon_perf_observe_event_bound(struct damon_perf_event *event,
+ int cpu, struct perf_event *perf_event);
+void damon_perf_observe_event_enabled(struct damon_perf_event *event,
+ int cpu, int state, int oncpu);
+void damon_perf_observe_event_disabled(struct damon_perf_event *event,
+ int cpu, int state);
+void damon_perf_observe_event_destroyed(struct damon_perf_event *event,
+ int cpu);
+void damon_perf_observe_event_free(struct damon_perf_event *event);
+
+/*
+ * Sample observed — NMI-safe.
+ *
+ * @reason: 0 = valid (queued to ring)
+ * 1 = data NULL
+ * 2 = addr == 0 (PMU did not populate)
+ * 3 = kernel address (vaddr only)
+ * 4 = phys_addr not valid (paddr only)
+ */
+void damon_perf_observe_sample(unsigned long addr, u64 data_src,
+ u64 period, int cpu, u8 reason,
+ u64 sample_flags, u64 sample_type);
+
+/* Ring operations — enqueue/overflow are NMI-safe */
+void damon_perf_observe_ring_enqueue(void);
+void damon_perf_observe_ring_overflow(int cpu);
+void damon_perf_observe_ring_dequeue(int cpu);
+void damon_perf_observe_ring_peak(unsigned int occupancy);
+
+/* Matching — process context (kdamond drain loop) */
+void damon_perf_observe_match(unsigned long addr, int cpu);
+void damon_perf_observe_miss(unsigned long addr, int cpu, int reason);
+void damon_perf_observe_update(int cpu);
+void damon_perf_observe_drain(unsigned int total, unsigned int matched);
+
+/* Debugfs (debug-only, format unstable) */
+int damon_perf_debugfs_init(void);
+
+/* Per-CPU stats accessors (for debugfs) */
+void damon_perf_stats_snapshot(int cpu, struct damon_perf_stats *dst);
+void damon_perf_stats_aggregate(struct damon_perf_stats *dst);
+
+/* Subsystem init */
+int damon_perf_framework_init(void);
+
+#else /* !CONFIG_DAMON_PERF_OBSERVE */
+
+static inline void damon_perf_observe_event_created(struct damon_perf_event *e,
+ int c)
+{
+}
+
+static inline void damon_perf_observe_event_bound(struct damon_perf_event *e,
+ int c, struct perf_event *p)
+{
+}
+
+static inline void damon_perf_observe_event_enabled(struct damon_perf_event *e,
+ int c, int s, int o)
+{
+}
+
+static inline void damon_perf_observe_event_disabled(struct damon_perf_event *e,
+ int c, int s)
+{
+}
+
+static inline void damon_perf_observe_event_destroyed(struct damon_perf_event *e,
+ int c)
+{
+}
+
+static inline void damon_perf_observe_event_free(struct damon_perf_event *e)
+{
+}
+
+static inline void damon_perf_observe_sample(unsigned long a, u64 d, u64 p,
+ int c, u8 r, u64 f, u64 t)
+{
+}
+
+static inline void damon_perf_observe_ring_enqueue(void)
+{
+}
+
+static inline void damon_perf_observe_ring_overflow(int c)
+{
+}
+
+static inline void damon_perf_observe_ring_dequeue(int c)
+{
+}
+
+static inline void damon_perf_observe_ring_peak(unsigned int o)
+{
+}
+
+static inline void damon_perf_observe_match(unsigned long a, int c)
+{
+}
+
+static inline void damon_perf_observe_miss(unsigned long a, int c, int r)
+{
+}
+
+static inline void damon_perf_observe_update(int c)
+{
+}
+
+static inline void damon_perf_observe_drain(unsigned int t, unsigned int m)
+{
+}
+
+static inline int damon_perf_debugfs_init(void)
+{
+ return 0;
+}
+
+static inline void damon_perf_stats_snapshot(int c, struct damon_perf_stats *d)
+{
+ memset(d, 0, sizeof(*d));
+}
+
+static inline void damon_perf_stats_aggregate(struct damon_perf_stats *d)
+{
+ memset(d, 0, sizeof(*d));
+}
+
+static inline int damon_perf_framework_init(void)
+{
+ return 0;
+}
+
+#endif /* CONFIG_DAMON_PERF_OBSERVE */
+
+#endif /* _DAMON_PERF_H */
--
2.43.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [RFC PATCH 2/7] mm/damon/perf: implement observe API and per-CPU statistics engine
2026-08-18 6:10 [RFC PATCH 0/7] mm/damon/perf: observability framework for hardware-sampled access reports Kunwu Chan
2026-08-18 6:10 ` [RFC PATCH 1/7] mm/damon/perf: add observability framework with tracepoints and CONFIG switch Kunwu Chan
@ 2026-08-18 6:10 ` Kunwu Chan
2026-08-18 6:10 ` [RFC PATCH 3/7] mm/damon/perf: add debugfs statistics interface Kunwu Chan
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: Kunwu Chan @ 2026-08-18 6:10 UTC (permalink / raw)
To: sj, akpm
Cc: damon, linux-mm, linux-kernel, linux-trace-kernel,
linux-kselftest, rostedt, mhiramat, mathieu.desnoyers, shuah,
lianux.mm, Kunwu Chan
From: Kunwu Chan <kunwu.chan@gmail.com>
Implement the observe_*() core: per-CPU monotonic counters, the
event-lifecycle hooks with lazily-allocated per-event per-CPU state
alongside the global per-CPU stage, NMI-safe sample classification,
ring enqueue/dequeue/peak, match/miss/update, and framework init. The
global per-CPU stage advances monotonically so a late create/bind/
enable cannot regress a CPU that is already RUNNING.
damon_perf_observe_sample() records the execution context
(process/softirq/hardirq/NMI) so overflow callbacks can be verified to
fire in the expected context.
Co-developed-by: Lian Wang <lianux.mm@gmail.com>
Signed-off-by: Lian Wang <lianux.mm@gmail.com>
Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
---
mm/damon/perf/Makefile | 2 +
mm/damon/perf/stats.c | 295 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 297 insertions(+)
create mode 100644 mm/damon/perf/stats.c
diff --git a/mm/damon/perf/Makefile b/mm/damon/perf/Makefile
index cc0d4f1d1d28..5c46d3da7ef8 100644
--- a/mm/damon/perf/Makefile
+++ b/mm/damon/perf/Makefile
@@ -1,3 +1,5 @@
# SPDX-License-Identifier: GPL-2.0
# Observability: per-CPU counters, tracepoints, debugfs perf_stats
+obj-$(CONFIG_DAMON_PERF_OBSERVE) += damon-perf.o
+damon-perf-objs := stats.o
diff --git a/mm/damon/perf/stats.c b/mm/damon/perf/stats.c
new file mode 100644
index 000000000000..a869f115bb26
--- /dev/null
+++ b/mm/damon/perf/stats.c
@@ -0,0 +1,295 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * DAMON Perf Observability — Per-CPU Statistics & Observe API
+ *
+ * All hardware-sampling backends funnel through the observe functions
+ * defined here. Counters always increment when
+ * CONFIG_DAMON_PERF_OBSERVE=y; tracepoints are guarded by
+ * trace_*_enabled() for zero overhead when ftrace is not attached.
+ *
+ * Per-CPU counters are best-effort: individual u64 writes are atomic
+ * on 64-bit platforms, but no cross-field consistency is guaranteed.
+ * Snapshot reads may race with concurrent writers. This is debug data
+ * — do not build policy on it.
+ */
+
+#include <linux/cpu.h>
+#include <linux/percpu.h>
+
+#include <trace/events/damon.h>
+
+#include "perf.h"
+
+/*
+ * Per-CPU statistics
+ */
+static DEFINE_PER_CPU(struct damon_perf_stats, damon_perf_stats);
+
+/*
+ * Per-CPU event state for the state machine — the maximum lifecycle
+ * stage ever reached on each CPU (any event). Set by the NMI
+ * observe_sample() (ENABLED→RUNNING) and by lifecycle functions as a
+ * monotonic "best CPU so far". Never reset to UNINIT — destroying one
+ * event must not hide that another event is still running on the same
+ * CPU. Per-event per-CPU state (event->cpu_state) tracks individual
+ * event lifecycle for correctness when multiple events exist.
+ */
+static DEFINE_PER_CPU(int, damon_perf_cpu_state);
+
+/*
+ * Event lifecycle — process context (kdamond / cpuhp callbacks).
+ *
+ * Each event tracks its own per-CPU lifecycle state via
+ * event->cpu_state (allocated on first CREATED, freed on DESTROYED).
+ * The global damon_perf_cpu_state is also advanced (monotonic) so that
+ * debugfs perf_stats shows the "best" stage any event reached on each
+ * CPU. Diagnostics are emitted via tracepoints, not dmesg.
+ */
+
+/*
+ * Advance the global per-CPU lifecycle state monotonically. The global
+ * reflects the best stage any event ever reached on this CPU; a late
+ * create/bind/enable must not regress a CPU that is already RUNNING.
+ */
+static void damon_perf_cpu_state_advance(int cpu, int state)
+{
+ int cur = READ_ONCE(per_cpu(damon_perf_cpu_state, cpu));
+
+ if (state > cur)
+ WRITE_ONCE(per_cpu(damon_perf_cpu_state, cpu), state);
+}
+
+void damon_perf_observe_event_created(struct damon_perf_event *event, int cpu)
+{
+ if (!event->cpu_state) {
+ event->cpu_state = alloc_percpu(int);
+ if (!event->cpu_state)
+ return;
+ }
+ *per_cpu_ptr(event->cpu_state, cpu) = DAMON_PERF_STATE_CREATED;
+ damon_perf_cpu_state_advance(cpu, DAMON_PERF_STATE_CREATED);
+}
+
+void damon_perf_observe_event_bound(struct damon_perf_event *event,
+ int cpu, struct perf_event *perf_event)
+{
+ if (event->cpu_state)
+ *per_cpu_ptr(event->cpu_state, cpu) = DAMON_PERF_STATE_BOUND;
+ damon_perf_cpu_state_advance(cpu, DAMON_PERF_STATE_BOUND);
+}
+
+void damon_perf_observe_event_enabled(struct damon_perf_event *event,
+ int cpu, int state, int oncpu)
+{
+ if (event->cpu_state)
+ *per_cpu_ptr(event->cpu_state, cpu) = DAMON_PERF_STATE_ENABLED;
+ damon_perf_cpu_state_advance(cpu, DAMON_PERF_STATE_ENABLED);
+}
+
+void damon_perf_observe_event_disabled(struct damon_perf_event *event,
+ int cpu, int state)
+{
+ /* State unchanged: the event may be re-enabled later. */
+}
+
+void damon_perf_observe_event_destroyed(struct damon_perf_event *event, int cpu)
+{
+ /*
+ * Reset only this CPU's slot. The per-CPU array is owned by the
+ * event as a whole and must NOT be freed here: destroyed() is
+ * invoked from the per-CPU CPU-offline callback, so freeing the
+ * whole array on the first offline CPU would leave every other
+ * still-online CPU with a dangling pointer. The array is freed
+ * once by damon_perf_observe_event_free() at event teardown.
+ */
+ if (event->cpu_state)
+ *per_cpu_ptr(event->cpu_state, cpu) = DAMON_PERF_STATE_UNINIT;
+}
+
+void damon_perf_observe_event_free(struct damon_perf_event *event)
+{
+ if (event->cpu_state) {
+ free_percpu(event->cpu_state);
+ event->cpu_state = NULL;
+ }
+}
+
+/*
+ * Sample observed — NMI-safe.
+ *
+ * The @cpu argument is the CPU the sample fired on; it is passed
+ * through to the tracepoint but stats are always written on the
+ * current CPU via this_cpu_ptr().
+ */
+
+void damon_perf_observe_sample(unsigned long addr, u64 data_src,
+ u64 period, int cpu, u8 reason,
+ u64 sample_flags, u64 sample_type)
+{
+ this_cpu_inc(damon_perf_stats.callback);
+
+ switch (reason) {
+ case 0:
+ this_cpu_inc(damon_perf_stats.sample_valid);
+ break;
+ case 1:
+ this_cpu_inc(damon_perf_stats.sample_null);
+ break;
+ case 2:
+ this_cpu_inc(damon_perf_stats.sample_addr_zero);
+ break;
+ case 3:
+ this_cpu_inc(damon_perf_stats.sample_kernel);
+ break;
+ case 4:
+ this_cpu_inc(damon_perf_stats.sample_invalid_phys);
+ break;
+ }
+
+ /* First callback advances state to RUNNING */
+ if (this_cpu_read(damon_perf_cpu_state) == DAMON_PERF_STATE_ENABLED)
+ this_cpu_write(damon_perf_cpu_state, DAMON_PERF_STATE_RUNNING);
+
+ /*
+ * Record the execution context so callers can verify whether
+ * overflow callbacks actually fire in the expected context
+ * (e.g. NMI for IBS, process for SPE AUX drain).
+ *
+ * 0 = process, 1 = softirq, 2 = hardirq, 3 = NMI
+ */
+ if (trace_damon_perf_sample_enabled())
+ trace_damon_perf_sample(addr, data_src, period, cpu, reason,
+ sample_flags, sample_type,
+ in_nmi() ? 3 : in_hardirq() ? 2 :
+ in_serving_softirq() ? 1 : 0);
+}
+
+/*
+ * Ring operations — enqueue / overflow are NMI-safe
+ */
+
+void damon_perf_observe_ring_enqueue(void)
+{
+ this_cpu_inc(damon_perf_stats.enqueue);
+}
+
+void damon_perf_observe_ring_overflow(int cpu)
+{
+ this_cpu_inc(damon_perf_stats.overflow);
+ if (trace_damon_perf_ring_overflow_enabled())
+ trace_damon_perf_ring_overflow(cpu);
+}
+
+void damon_perf_observe_ring_dequeue(int cpu)
+{
+ per_cpu_ptr(&damon_perf_stats, cpu)->dequeue++;
+}
+
+void damon_perf_observe_ring_peak(unsigned int occupancy)
+{
+ struct damon_perf_stats *st = this_cpu_ptr(&damon_perf_stats);
+
+ if (occupancy > READ_ONCE(st->ring_peak))
+ WRITE_ONCE(st->ring_peak, occupancy);
+}
+
+/*
+ * Matching — process context (kdamond drain loop)
+ */
+
+void damon_perf_observe_match(unsigned long addr, int cpu)
+{
+ per_cpu_ptr(&damon_perf_stats, cpu)->match++;
+}
+
+void damon_perf_observe_miss(unsigned long addr, int cpu, int reason)
+{
+ struct damon_perf_stats *st = per_cpu_ptr(&damon_perf_stats, cpu);
+
+ switch (reason) {
+ case DAMON_REPORT_MISS_TGID:
+ st->miss_tgid++;
+ break;
+ case DAMON_REPORT_MISS_NOREGION:
+ st->miss_region++;
+ break;
+ case DAMON_REPORT_MISS_BOUNDARY:
+ st->miss_boundary++;
+ break;
+ }
+
+ if (trace_damon_perf_report_missed_enabled())
+ trace_damon_perf_report_missed(addr, cpu, reason);
+}
+
+void damon_perf_observe_update(int cpu)
+{
+ per_cpu_ptr(&damon_perf_stats, cpu)->update++;
+}
+
+void damon_perf_observe_drain(unsigned int total, unsigned int matched)
+{
+ if (trace_damon_perf_drain_enabled())
+ trace_damon_perf_drain(total, matched);
+}
+
+/*
+ * Stats accessors (for debugfs)
+ */
+
+/*
+ * Best-effort per-CPU snapshot. Individual u64 writes are atomic on
+ * 64-bit platforms; no cross-field consistency is guaranteed. This is
+ * debug data only — do not build policy on it.
+ */
+void damon_perf_stats_snapshot(int cpu, struct damon_perf_stats *dst)
+{
+ struct damon_perf_stats *st = per_cpu_ptr(&damon_perf_stats, cpu);
+
+ *dst = *st;
+ dst->cpu_state = per_cpu(damon_perf_cpu_state, cpu);
+}
+
+void damon_perf_stats_aggregate(struct damon_perf_stats *dst)
+{
+ int cpu;
+
+ memset(dst, 0, sizeof(*dst));
+ dst->cpu_state = DAMON_PERF_STATE_RUNNING; /* start optimistic, take min */
+ cpus_read_lock();
+ for_each_online_cpu(cpu) {
+ struct damon_perf_stats *st = per_cpu_ptr(&damon_perf_stats, cpu);
+
+ dst->callback += st->callback;
+ dst->sample_valid += st->sample_valid;
+ dst->sample_null += st->sample_null;
+ dst->sample_addr_zero += st->sample_addr_zero;
+ dst->sample_kernel += st->sample_kernel;
+ dst->sample_invalid_phys += st->sample_invalid_phys;
+ dst->enqueue += st->enqueue;
+ dst->dequeue += st->dequeue;
+ dst->overflow += st->overflow;
+ dst->ring_peak = max(dst->ring_peak, st->ring_peak);
+ dst->match += st->match;
+ dst->miss_tgid += st->miss_tgid;
+ dst->miss_region += st->miss_region;
+ dst->miss_boundary += st->miss_boundary;
+ dst->update += st->update;
+ /*
+ * Aggregate per-CPU state: the pipeline hasn't passed a
+ * stage until ALL CPUs have passed it, so take the min.
+ */
+ dst->cpu_state = min_t(int, dst->cpu_state,
+ per_cpu(damon_perf_cpu_state, cpu));
+ }
+ cpus_read_unlock();
+}
+
+/*
+ * Subsystem init
+ */
+
+int damon_perf_framework_init(void)
+{
+ return 0;
+}
--
2.43.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [RFC PATCH 3/7] mm/damon/perf: add debugfs statistics interface
2026-08-18 6:10 [RFC PATCH 0/7] mm/damon/perf: observability framework for hardware-sampled access reports Kunwu Chan
2026-08-18 6:10 ` [RFC PATCH 1/7] mm/damon/perf: add observability framework with tracepoints and CONFIG switch Kunwu Chan
2026-08-18 6:10 ` [RFC PATCH 2/7] mm/damon/perf: implement observe API and per-CPU statistics engine Kunwu Chan
@ 2026-08-18 6:10 ` Kunwu Chan
2026-08-18 6:10 ` [RFC PATCH 4/7] mm/damon: integrate observe API into vaddr overflow handlers and core drain Kunwu Chan
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: Kunwu Chan @ 2026-08-18 6:10 UTC (permalink / raw)
To: sj, akpm
Cc: damon, linux-mm, linux-kernel, linux-trace-kernel,
linux-kselftest, rostedt, mhiramat, mathieu.desnoyers, shuah,
lianux.mm, Kunwu Chan
From: Lian Wang <lianux.mm@gmail.com>
Expose the aggregated per-CPU counters and the global event-stage in a
debug-only debugfs perf_stats file. The format is explicitly unstable;
tracepoints are the stable diagnostic interface.
Co-developed-by: Kunwu Chan <kunwu.chan@gmail.com>
Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
Signed-off-by: Lian Wang <lianux.mm@gmail.com>
---
mm/damon/perf/Makefile | 2 +-
mm/damon/perf/debugfs.c | 142 ++++++++++++++++++++++++++++++++++++++++
mm/damon/perf/stats.c | 2 +-
3 files changed, 144 insertions(+), 2 deletions(-)
create mode 100644 mm/damon/perf/debugfs.c
diff --git a/mm/damon/perf/Makefile b/mm/damon/perf/Makefile
index 5c46d3da7ef8..150cbaa875fa 100644
--- a/mm/damon/perf/Makefile
+++ b/mm/damon/perf/Makefile
@@ -2,4 +2,4 @@
# Observability: per-CPU counters, tracepoints, debugfs perf_stats
obj-$(CONFIG_DAMON_PERF_OBSERVE) += damon-perf.o
-damon-perf-objs := stats.o
+damon-perf-objs := stats.o debugfs.o
diff --git a/mm/damon/perf/debugfs.c b/mm/damon/perf/debugfs.c
new file mode 100644
index 000000000000..c54dd7644ac3
--- /dev/null
+++ b/mm/damon/perf/debugfs.c
@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * DAMON Perf Observability — debugfs Interface
+ *
+ * Exposes one file under /sys/kernel/debug/damon/:
+ *
+ * perf_stats — per-CPU pipeline statistics in tabular form
+ *
+ * DEBUG ONLY — format may change without notice; do not parse in
+ * scripts. For stable diagnostics, use the tracepoints under
+ * /sys/kernel/debug/tracing/events/damon/
+ */
+
+#include <linux/cpu.h>
+#include <linux/cpumask.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+
+#include "perf.h"
+
+static struct dentry *damon_debugfs_dir;
+
+/*
+ * perf_stats
+ */
+
+static const char *state_name(int s)
+{
+ switch (s) {
+ case DAMON_PERF_STATE_UNINIT: return "UNINIT";
+ case DAMON_PERF_STATE_CREATED: return "CREATED";
+ case DAMON_PERF_STATE_BOUND: return "BOUND";
+ case DAMON_PERF_STATE_ENABLED: return "ENABLED";
+ case DAMON_PERF_STATE_RUNNING: return "RUNNING";
+ case DAMON_PERF_STATE_ERROR: return "ERROR";
+ default: return "?";
+ }
+}
+
+static int perf_stats_show(struct seq_file *m, void *v)
+{
+ struct damon_perf_stats agg, st;
+ int cpu;
+ bool first = true;
+
+ damon_perf_stats_aggregate(&agg);
+
+ seq_puts(m, " -------------- ----------\n");
+ seq_puts(m, " Counter Value\n");
+ seq_puts(m, " -------------- ----------\n");
+
+#define STAT_ROW(label, field) \
+ seq_printf(m, " %-12s %8llu\n", label, agg.field)
+
+ STAT_ROW("callback", callback);
+ STAT_ROW("valid", sample_valid);
+ STAT_ROW("null", sample_null);
+ STAT_ROW("addr_zero", sample_addr_zero);
+ STAT_ROW("kernel", sample_kernel);
+ STAT_ROW("inv_phys", sample_invalid_phys);
+ STAT_ROW("enqueue", enqueue);
+ STAT_ROW("dequeue", dequeue);
+ STAT_ROW("overflow", overflow);
+ STAT_ROW("ring_peak", ring_peak);
+ STAT_ROW("match", match);
+ STAT_ROW("miss_tgid", miss_tgid);
+ STAT_ROW("miss_region", miss_region);
+ STAT_ROW("miss_bound", miss_boundary);
+ STAT_ROW("update", update);
+
+#undef STAT_ROW
+
+ seq_puts(m, " -------------- ----------\n\n");
+
+ /* Per-CPU breakdown */
+ cpus_read_lock();
+ for_each_online_cpu(cpu) {
+ damon_perf_stats_snapshot(cpu, &st);
+
+ /* Skip truly idle CPUs */
+ if (st.cpu_state == DAMON_PERF_STATE_UNINIT &&
+ !st.callback && !st.enqueue && !st.dequeue)
+ continue;
+
+ if (first) {
+ seq_puts(m, " Per-CPU (non-zero / non-UNINIT):\n");
+ first = false;
+ }
+
+ seq_printf(m, " CPU%02d: st=%-7s cb=%llu enq=%llu deq=%llu ovf=%llu match=%llu tgid=%llu noreg=%llu bound=%llu upd=%llu\n",
+ cpu, state_name(st.cpu_state),
+ st.callback, st.enqueue, st.dequeue,
+ st.overflow, st.match,
+ st.miss_tgid, st.miss_region, st.miss_boundary,
+ st.update);
+ }
+ cpus_read_unlock();
+
+ return 0;
+}
+
+static int perf_stats_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, perf_stats_show, NULL);
+}
+
+static const struct file_operations perf_stats_fops = {
+ .open = perf_stats_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+
+/*
+ * Init / teardown
+ */
+
+int damon_perf_debugfs_init(void)
+{
+ if (!debugfs_initialized())
+ return -ENODEV;
+
+ /*
+ * Create the "damon" directory first. debugfs_create_dir() mounts
+ * debugfs via simple_pin_fs() before touching debugfs_mount, so it
+ * is safe to call during initcall time -- unlike debugfs_lookup(),
+ * which dereferences debugfs_mount unconditionally and crashes with
+ * a NULL mount. If the directory already exists (created by another
+ * DAMON interface) debugfs_create_dir() returns -EEXIST; fall back
+ * to debugfs_lookup(), which is now safe because the mount exists.
+ */
+ damon_debugfs_dir = debugfs_create_dir("damon", NULL);
+ if (damon_debugfs_dir == ERR_PTR(-EEXIST))
+ damon_debugfs_dir = debugfs_lookup("damon", NULL);
+ if (IS_ERR(damon_debugfs_dir))
+ return PTR_ERR(damon_debugfs_dir);
+
+ debugfs_create_file("perf_stats", 0400, damon_debugfs_dir,
+ NULL, &perf_stats_fops);
+
+ return 0;
+}
diff --git a/mm/damon/perf/stats.c b/mm/damon/perf/stats.c
index a869f115bb26..ae5b0037a31d 100644
--- a/mm/damon/perf/stats.c
+++ b/mm/damon/perf/stats.c
@@ -291,5 +291,5 @@ void damon_perf_stats_aggregate(struct damon_perf_stats *dst)
int damon_perf_framework_init(void)
{
- return 0;
+ return damon_perf_debugfs_init();
}
--
2.43.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [RFC PATCH 4/7] mm/damon: integrate observe API into vaddr overflow handlers and core drain
2026-08-18 6:10 [RFC PATCH 0/7] mm/damon/perf: observability framework for hardware-sampled access reports Kunwu Chan
` (2 preceding siblings ...)
2026-08-18 6:10 ` [RFC PATCH 3/7] mm/damon/perf: add debugfs statistics interface Kunwu Chan
@ 2026-08-18 6:10 ` Kunwu Chan
2026-08-18 6:10 ` [RFC PATCH 5/7] selftests/damon: add automated layer-by-layer observability test Kunwu Chan
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: Kunwu Chan @ 2026-08-18 6:10 UTC (permalink / raw)
To: sj, akpm
Cc: damon, linux-mm, linux-kernel, linux-trace-kernel,
linux-kselftest, rostedt, mhiramat, mathieu.desnoyers, shuah,
lianux.mm, Kunwu Chan
From: Kunwu Chan <kunwu.chan@gmail.com>
Wire the observe_*() calls into the DAMON hot paths: vaddr access-check
overflow handlers report into the per-CPU ring, and the kdamond drain
matches each report against the target whose tgid owns it. The observe
calls are pure side-effect statistics (no-ops under
CONFIG_DAMON_PERF_OBSERVE=n), so the switch never changes DAMON matching
semantics. The vaddr teardown frees the per-event cpu_state array.
Read ring->tail once with READ_ONCE in damon_report_access() and reuse
the cached value for the peak-occupancy estimate, avoiding a torn read
and a compiler reload on the producer side.
Co-developed-by: Lian Wang <lianux.mm@gmail.com>
Signed-off-by: Lian Wang <lianux.mm@gmail.com>
Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
---
mm/damon/core.c | 129 +++++++++++++++++++++++++++++++++++++----------
mm/damon/vaddr.c | 104 +++++++++++++++++++++++++++++++++++---
2 files changed, 199 insertions(+), 34 deletions(-)
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 609d627e2b33..377f07122fb0 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -21,6 +21,7 @@
/* for damon_get_folio() used by node eligible memory metrics */
#include "ops-common.h"
+#include "perf/perf.h"
#define CREATE_TRACE_POINTS
#include <trace/events/damon.h>
@@ -2243,24 +2244,41 @@ void damon_report_access(struct damon_access_report *report)
preempt_disable();
if (local_inc_return(this_cpu_ptr(&damon_report_ring_busy)) != 1) {
/* NMI nested on a process-context producer; drop. */
- trace_damon_perf_ring_overflow(smp_processor_id());
+#ifdef CONFIG_DAMON_PERF_OBSERVE
+ damon_perf_observe_ring_overflow(smp_processor_id());
+#endif /* CONFIG_DAMON_PERF_OBSERVE */
goto out;
}
ring = this_cpu_ptr(&damon_report_rings);
head = ring->head;
next = (head + 1) & DAMON_REPORT_RING_MASK;
+ {
+ unsigned int tail = READ_ONCE(ring->tail);
- if (next == READ_ONCE(ring->tail)) {
- trace_damon_perf_ring_overflow(smp_processor_id());
- goto out;
- }
+ if (next == tail) {
+#ifdef CONFIG_DAMON_PERF_OBSERVE
+ damon_perf_observe_ring_overflow(smp_processor_id());
+#endif /* CONFIG_DAMON_PERF_OBSERVE */
+ goto out;
+ }
- ring->entries[head] = *report;
- ring->entries[head].report_jiffies = jiffies;
- smp_wmb(); /* publish entry before head advance */
- WRITE_ONCE(ring->head, next);
- WRITE_ONCE(*this_cpu_ptr(&damon_ring_pending), 1);
+ ring->entries[head] = *report;
+ ring->entries[head].report_jiffies = jiffies;
+ smp_wmb(); /* publish entry before head advance */
+ WRITE_ONCE(ring->head, next);
+ WRITE_ONCE(*this_cpu_ptr(&damon_ring_pending), 1);
+#ifdef CONFIG_DAMON_PERF_OBSERVE
+ damon_perf_observe_ring_enqueue();
+ /*
+ * Track peak occupancy for health evaluation.
+ * next is the new head; tail was read before enqueue
+ * (may be slightly stale — acceptable for a peak estimate).
+ */
+ damon_perf_observe_ring_peak(
+ (next - tail) & DAMON_REPORT_RING_MASK);
+#endif /* CONFIG_DAMON_PERF_OBSERVE */
+ }
out:
local_dec(this_cpu_ptr(&damon_report_ring_busy));
preempt_enable();
@@ -2276,6 +2294,9 @@ void damon_report_page_fault(struct vm_fault *vmf, bool huge_pmd)
.tid = current->pid,
.tgid = task_tgid_nr(current),
.is_write = vmf->flags & FAULT_FLAG_WRITE,
+#ifdef CONFIG_DAMON_PERF_OBSERVE
+ .source = DAMON_REPORT_SRC_PAGE_FAULT,
+#endif /* CONFIG_DAMON_PERF_OBSERVE */
};
if (huge_pmd)
@@ -3917,8 +3938,16 @@ static bool damon_sample_filter_out(struct damon_access_report *report,
return !filter->allow;
}
-static void kdamond_apply_access_report(struct damon_access_report *report,
- struct damon_target *t,
+/*
+ * Try to apply one access report to a target's region snapshot.
+ *
+ * Caller has already resolved tgid (for pid-based monitoring), so this
+ * function only does address-to-region matching. Miss reasons for
+ * trace_damon_perf_report_missed use enum damon_report_miss_reason.
+ *
+ * Return: true if the report fell inside a known region, false otherwise.
+ */
+static bool kdamond_apply_access_report(struct damon_access_report *report,
struct damon_region **regions, unsigned int nr_regions,
struct damon_ctx *ctx)
{
@@ -3926,13 +3955,7 @@ static void kdamond_apply_access_report(struct damon_access_report *report,
unsigned long addr;
int left, right, mid;
- if (damon_target_has_pid(ctx)) {
- if (pid_nr(t->pid) != report->tgid)
- return;
- addr = report->vaddr;
- } else {
- addr = report->paddr;
- }
+ addr = damon_target_has_pid(ctx) ? report->vaddr : report->paddr;
/* Binary search the snapshot for the region containing addr. */
left = 0;
@@ -3951,17 +3974,27 @@ static void kdamond_apply_access_report(struct damon_access_report *report,
}
}
- if (!r)
- return;
+ if (!r) {
+ damon_perf_observe_miss(addr, report->cpu,
+ DAMON_REPORT_MISS_NOREGION);
+ return false;
+ }
/* Reject reports straddling a region boundary. */
- if (addr + report->size > r->ar.end)
- return;
+ if (addr + report->size > r->ar.end) {
+ damon_perf_observe_miss(addr, report->cpu,
+ DAMON_REPORT_MISS_BOUNDARY);
+ return false;
+ }
if (!r->access_reported) {
damon_update_region_access_rate(r, true, &ctx->attrs);
r->access_reported = true;
+ damon_perf_observe_update(report->cpu);
}
+ damon_perf_observe_match(addr, report->cpu);
+ return true;
}
+
static unsigned int kdamond_apply_zero_access_report(struct damon_ctx *ctx)
{
struct damon_target *t;
@@ -4045,6 +4078,7 @@ static unsigned int kdamond_check_reported_accesses(struct damon_ctx *ctx)
struct damon_target_lookup *tbl;
unsigned int nr_targets = 0;
unsigned int i;
+ unsigned int total_reports = 0, matched_reports = 0;
tbl = damon_build_target_lookup(ctx, &nr_targets);
if (!tbl) {
@@ -4077,6 +4111,10 @@ static unsigned int kdamond_check_reported_accesses(struct damon_ctx *ctx)
while (tail != head) {
struct damon_access_report *report =
&ring->entries[tail];
+ bool applied = false;
+
+ /* Count every entry removed from the ring */
+ damon_perf_observe_ring_dequeue(report->cpu);
if (time_before(report->report_jiffies,
jiffies - usecs_to_jiffies(
@@ -4085,16 +4123,52 @@ static unsigned int kdamond_check_reported_accesses(struct damon_ctx *ctx)
if (damon_sample_filter_out(report,
&ctx->sample_control))
goto next;
- for (i = 0; i < nr_targets; i++)
- kdamond_apply_access_report(report,
- tbl[i].t,
+ /*
+ * For pid-based monitoring, resolve tgid to the
+ * single matching target before calling
+ * kdamond_apply_access_report(), avoiding a
+ * spurious miss tracepoint for every non-matching
+ * target.
+ */
+ if (damon_target_has_pid(ctx)) {
+ for (i = 0; i < nr_targets; i++) {
+ if (pid_nr(tbl[i].t->pid) ==
+ report->tgid) {
+ applied =
+ kdamond_apply_access_report(
+ report,
+ tbl[i].regions,
+ tbl[i].nr_regions,
+ ctx);
+ break;
+ }
+ }
+ if (!applied && i == nr_targets)
+ damon_perf_observe_miss(
+ report->vaddr,
+ report->cpu,
+ DAMON_REPORT_MISS_TGID);
+ } else {
+ for (i = 0; i < nr_targets; i++)
+ applied |=
+ kdamond_apply_access_report(
+ report,
tbl[i].regions,
tbl[i].nr_regions, ctx);
+ }
+ total_reports++;
+ if (applied)
+ matched_reports++;
+
next:
tail = (tail + 1) & DAMON_REPORT_RING_MASK;
}
WRITE_ONCE(ring->tail, tail);
}
+
+ if (total_reports)
+ damon_perf_observe_drain(total_reports, matched_reports);
+
/* For nr_accesses_bp, absence of access should also be reported. */
return kdamond_apply_zero_access_report(ctx);
}
@@ -4158,8 +4232,9 @@ static int kdamond_fn(void *data)
ctx->passed_sample_intervals++;
if (!list_empty(&ctx->perf_events) ||
- ctx->sample_control.primitives_enabled.page_fault)
+ ctx->sample_control.primitives_enabled.page_fault) {
max_nr_accesses = kdamond_check_reported_accesses(ctx);
+ }
else if (ctx->ops.check_accesses)
max_nr_accesses = ctx->ops.check_accesses(ctx);
if (ctx->ops.apply_probes)
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 73fcea91afa0..a68c7262d533 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -17,6 +17,8 @@
#include <linux/pagewalk.h>
#include <linux/sched/mm.h>
+#include "perf/perf.h"
+
#include "../internal.h"
#include "ops-common.h"
@@ -975,13 +977,49 @@ static void damon_perf_overflow_vaddr(struct perf_event *perf_event,
struct perf_sample_data *data, struct pt_regs *regs)
{
struct damon_access_report report;
+ u64 data_src_val;
+ u64 period_val;
+
+ /*
+ * Observe every hardware sample through the unified API.
+ *
+ * reason encodes why a sample was dropped at the handler level:
+ * 0 = valid, queued to ring
+ * 1 = data == NULL
+ * 2 = addr == 0 (PMU did not populate data->addr)
+ * 3 = kernel address (addr >= TASK_SIZE)
+ */
+ if (!data) {
+ damon_perf_observe_sample(0, 0, 0,
+ smp_processor_id(), 1, 0,
+ perf_event->attr.sample_type);
+ return;
+ }
- if (!data || !data->addr)
+ data_src_val = data->data_src.val;
+ period_val = data->period;
+
+ if (!data->addr) {
+ damon_perf_observe_sample(0, data_src_val, period_val,
+ smp_processor_id(), 2,
+ data->sample_flags,
+ perf_event->attr.sample_type);
return;
+ }
/* Drop kernel-VA hits -- only user-space VAs land in damon vaddr regions. */
- if (data->addr >= TASK_SIZE)
+ if (data->addr >= TASK_SIZE) {
+ damon_perf_observe_sample(data->addr, data_src_val, period_val,
+ smp_processor_id(), 3,
+ data->sample_flags,
+ perf_event->attr.sample_type);
return;
+ }
+
+ damon_perf_observe_sample(data->addr, data_src_val, period_val,
+ smp_processor_id(), 0,
+ data->sample_flags,
+ perf_event->attr.sample_type);
report = (struct damon_access_report){
.vaddr = data->addr & PAGE_MASK,
@@ -990,6 +1028,9 @@ static void damon_perf_overflow_vaddr(struct perf_event *perf_event,
.tid = current->pid,
.tgid = current->tgid,
.is_write = !!(data->data_src.mem_op & PERF_MEM_OP_STORE),
+#ifdef CONFIG_DAMON_PERF_OBSERVE
+ .source = DAMON_REPORT_SRC_PERF_OVERFLOW,
+#endif /* CONFIG_DAMON_PERF_OBSERVE */
};
damon_report_access(&report);
}
@@ -998,9 +1039,18 @@ static void damon_perf_overflow_paddr(struct perf_event *perf_event,
struct perf_sample_data *data, struct pt_regs *regs)
{
struct damon_access_report report;
+ u64 data_src_val;
+ u64 period_val;
- if (!data)
+ if (!data) {
+ damon_perf_observe_sample(0, 0, 0,
+ smp_processor_id(), 1, 0,
+ perf_event->attr.sample_type);
return;
+ }
+
+ data_src_val = data->data_src.val;
+ period_val = data->period;
/*
* AMD IBS Op only populates data->phys_addr when
@@ -1008,14 +1058,27 @@ static void damon_perf_overflow_paddr(struct perf_event *perf_event,
* carries a stale value. Gate on sample_flags rather than testing
* phys_addr for zero (which would also drop legitimate page 0).
*/
- if (!(data->sample_flags & PERF_SAMPLE_PHYS_ADDR))
+ if (!(data->sample_flags & PERF_SAMPLE_PHYS_ADDR)) {
+ damon_perf_observe_sample(0, data_src_val,
+ period_val, smp_processor_id(), 4,
+ data->sample_flags,
+ perf_event->attr.sample_type);
return;
+ }
+
+ damon_perf_observe_sample(data->phys_addr, data_src_val, period_val,
+ smp_processor_id(), 0,
+ data->sample_flags,
+ perf_event->attr.sample_type);
report = (struct damon_access_report){
.paddr = data->phys_addr & PAGE_MASK,
.size = PAGE_SIZE,
.cpu = smp_processor_id(),
.is_write = !!(data->data_src.mem_op & PERF_MEM_OP_STORE),
+#ifdef CONFIG_DAMON_PERF_OBSERVE
+ .source = DAMON_REPORT_SRC_PERF_OVERFLOW,
+#endif /* CONFIG_DAMON_PERF_OBSERVE */
};
damon_report_access(&report);
}
@@ -1070,6 +1133,8 @@ static int damon_perf_cpu_online(unsigned int cpu, struct hlist_node *node)
if (!perf)
return 0;
+ damon_perf_observe_event_created(event, cpu);
+
damon_perf_event_init_attr(event, &attr);
/*
@@ -1092,14 +1157,20 @@ static int damon_perf_cpu_online(unsigned int cpu, struct hlist_node *node)
return 0; /* never block CPU online */
}
*per_cpu_ptr(perf->event, cpu) = perf_event;
+
+ damon_perf_observe_event_bound(event, cpu, perf_event);
+
/*
* Late-online CPU after the substrate is armed: events are created
* with attr.disabled = 1 and would otherwise stay quiescent on this
* CPU until the next arm walk. Enable here so coverage matches the
* already-online CPUs.
*/
- if (event->ctx && READ_ONCE(event->ctx->perf_events_active))
+ if (event->ctx && READ_ONCE(event->ctx->perf_events_active)) {
perf_event_enable(perf_event);
+ damon_perf_observe_event_enabled(event, cpu,
+ perf_event->state, perf_event->oncpu);
+ }
return 0;
}
@@ -1115,6 +1186,7 @@ static int damon_perf_cpu_offline(unsigned int cpu, struct hlist_node *node)
perf_event = per_cpu(*perf->event, cpu);
if (perf_event) {
+ damon_perf_observe_event_destroyed(event, cpu);
perf_event_disable(perf_event);
perf_event_release_kernel(perf_event);
*per_cpu_ptr(perf->event, cpu) = NULL;
@@ -1133,8 +1205,12 @@ void damon_perf_event_arm(struct damon_perf_event *event)
for_each_online_cpu(cpu) {
perf_event = *per_cpu_ptr(perf->event, cpu);
- if (perf_event)
+ if (perf_event) {
perf_event_enable(perf_event);
+ damon_perf_observe_event_enabled(event, cpu,
+ perf_event->state,
+ perf_event->oncpu);
+ }
}
}
@@ -1149,8 +1225,11 @@ void damon_perf_event_disarm(struct damon_perf_event *event)
for_each_online_cpu(cpu) {
perf_event = *per_cpu_ptr(perf->event, cpu);
- if (perf_event)
+ if (perf_event) {
perf_event_disable(perf_event);
+ damon_perf_observe_event_disabled(event, cpu,
+ perf_event->state);
+ }
}
}
@@ -1192,6 +1271,7 @@ int damon_perf_init(struct damon_ctx *ctx, struct damon_perf_event *event)
return 0;
free_event:
+ damon_perf_observe_event_free(event);
free_percpu(perf->event);
free_perf:
kfree(perf);
@@ -1203,6 +1283,8 @@ void damon_perf_cleanup(struct damon_ctx *ctx, struct damon_perf_event *event)
{
struct damon_perf *perf = event->priv;
+ damon_perf_observe_event_free(event);
+
if (!perf)
return;
@@ -1244,6 +1326,14 @@ static int __init damon_va_initcall(void)
if (err < 0)
return err;
damon_perf_cpuhp_state = err;
+
+#ifdef CONFIG_DAMON_PERF_OBSERVE
+ err = damon_perf_framework_init();
+ if (err < 0)
+ pr_warn("damon-perf: framework init failed, observability unavailable: %d\n",
+ err);
+ /* Non-fatal: vaddr/fvaddr ops still register. */
+#endif /* CONFIG_DAMON_PERF_OBSERVE */
#endif
err = damon_register_ops(&ops);
--
2.43.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [RFC PATCH 5/7] selftests/damon: add automated layer-by-layer observability test
2026-08-18 6:10 [RFC PATCH 0/7] mm/damon/perf: observability framework for hardware-sampled access reports Kunwu Chan
` (3 preceding siblings ...)
2026-08-18 6:10 ` [RFC PATCH 4/7] mm/damon: integrate observe API into vaddr overflow handlers and core drain Kunwu Chan
@ 2026-08-18 6:10 ` Kunwu Chan
2026-08-18 6:10 ` [RFC PATCH 6/7] Docs/mm/damon: document the perf observability framework Kunwu Chan
2026-08-18 6:10 ` [RFC PATCH 7/7] mm/damon/perf: add CONFIG_DAMON_PERF_DEBUG and pipeline health check Kunwu Chan
6 siblings, 0 replies; 8+ messages in thread
From: Kunwu Chan @ 2026-08-18 6:10 UTC (permalink / raw)
To: sj, akpm
Cc: damon, linux-mm, linux-kernel, linux-trace-kernel,
linux-kselftest, rostedt, mhiramat, mathieu.desnoyers, shuah,
lianux.mm, Kunwu Chan
From: Kunwu Chan <kunwu.chan@gmail.com>
Drive the observe framework end-to-end with a software page-fault PMU
positive control (no hardware PMU required): create a kdamond with a
perf event via the DAMON sysfs interface, run a memory-pressure
workload, capture a bounded trace window, and assert each pipeline
layer from per-run snapshot/delta counter deltas (counters are
cumulative since boot, so the snapshot is taken before the workload
window): callbacks, valid data addresses, ring enqueue/dequeue/
overflow, drain match/update, the four DAMON perf tracepoints, and the
per-CPU state column advancing CREATED/BOUND/ENABLED to RUNNING after
the first callback.
A clean-session guard refuses to run while a kdamond already exists.
Ends with a PMU support verdict (FULLY INTEGRATED / PLUMBING-ONLY /
UNUSABLE). Cleanup is ownership safe: it tears down only the kdamond,
workload and debugfs mount created by this invocation, and retains the
raw evidence directory by default.
Co-developed-by: Lian Wang <lianux.mm@gmail.com>
Signed-off-by: Lian Wang <lianux.mm@gmail.com>
Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
---
tools/testing/selftests/damon/Makefile | 1 +
.../selftests/damon/damon_perf_obs_test.sh | 562 ++++++++++++++++++
2 files changed, 563 insertions(+)
create mode 100755 tools/testing/selftests/damon/damon_perf_obs_test.sh
diff --git a/tools/testing/selftests/damon/Makefile b/tools/testing/selftests/damon/Makefile
index 2180c328a825..1db8fa95ba2d 100644
--- a/tools/testing/selftests/damon/Makefile
+++ b/tools/testing/selftests/damon/Makefile
@@ -23,4 +23,5 @@ TEST_PROGS += sysfs_no_op_commit_break.py
EXTRA_CLEAN = __pycache__
+TEST_PROGS += damon_perf_obs_test.sh
include ../lib.mk
diff --git a/tools/testing/selftests/damon/damon_perf_obs_test.sh b/tools/testing/selftests/damon/damon_perf_obs_test.sh
new file mode 100755
index 000000000000..4c4074cdd191
--- /dev/null
+++ b/tools/testing/selftests/damon/damon_perf_obs_test.sh
@@ -0,0 +1,562 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# DAMON Perf Observability Framework — Automated Layer-by-Layer Test
+#
+# Validates all 7 pipeline stages:
+# Layer 1: Event Create Layer 2: Event Bind
+# Layer 3: Event Enable Layer 4: Sampling (callback)
+# Layer 5: Ring Layer 6: Drain
+# Layer 7: Match & Update
+#
+# The framework counters are cumulative since boot, so this script
+# snapshots them before the workload and reports per-run deltas. It
+# also clears the trace buffer before the sampling window so trace.txt
+# carries only records produced by this run.
+#
+# Usage:
+# # Software page-fault positive control (exercises the FULL pipeline,
+# # works on any machine, no HW PMU required). Defaults to sampling
+# # every page fault (period 1); override with --freq/--period:
+# sudo ./damon_perf_obs_test.sh --pmu software
+# sudo ./damon_perf_obs_test.sh --pmu software --freq 1 --sample-freq 100
+#
+# # With ARM SPE:
+# sudo ./damon_perf_obs_test.sh --pmu arm_spe_0 --freq 0 --period 256
+#
+# # With any PMU type number:
+# sudo ./damon_perf_obs_test.sh --pmu-type 38 --freq 0 --period 256
+#
+# Notes:
+# - `--config N` sets perf_event_attr.config. For PERF_TYPE_SOFTWARE,
+# config 2 (PERF_COUNT_SW_PAGE_FAULTS) is the only software event
+# that populates data->addr; cpu-clock (config 0) delivers callbacks
+# with addr always 0, so it can only validate Layers 1-4.
+# - ARM SPE cannot sample through perf_event_create_kernel_counter()
+# (it requires an AUX ring buffer, see arm_spe_pmu.c), so an SPE run
+# is expected to report zero callbacks until an AUX backend exists.
+# A zero-callback delta is the correct "PMU not usable" verdict.
+#
+# Requirements:
+# - CONFIG_DAMON_PERF_OBSERVE=y (fatal if missing)
+# - Root privileges
+# - debugfs mounted
+
+set -e
+
+# ---- defaults ----
+PMU_NAME=""
+PMU_TYPE=""
+PMU_CONFIG=0
+CONFIG_EXPLICIT=0
+FREQ=0
+PERIOD=256
+FREQ_EXPLICIT=0
+PERIOD_EXPLICIT=0
+SAMPLE_FREQ=100
+TIMEOUT=10
+TRACE_WINDOW=3
+TARGET_PID=""
+RESULTS_DIR="/tmp/damon_perf_test_$$"
+PASSED=0
+FAILED=0
+SKIPPED=0
+STRESS_PID=""
+CREATED_KDAMOND=0
+MOUNTED_DEBUGFS=0
+KEEP_RESULTS=${KEEP_RESULTS:-1}
+
+# ---- helpers ----
+pass() { echo " [PASS] $1"; PASSED=$((PASSED + 1)); }
+fail() { echo " [FAIL] $1 — $2"; FAILED=$((FAILED + 1)); }
+skip() { echo " [SKIP] $1 — $2"; SKIPPED=$((SKIPPED + 1)); }
+die() { echo "FATAL: $1"; exit 1; }
+
+# ---- sysfs roots (kept under 100 columns) ----
+KD=/sys/kernel/mm/damon/admin/kdamonds
+ADMIN=$KD/0
+TRACE=/sys/kernel/debug/tracing
+TPD=$TRACE/events/damon
+PE=$ADMIN/contexts/0/monitoring_attrs/sample/perf_events
+
+# ---- saved pre-test state (restored in cleanup so the test is
+# ---- side-effect free: tracepoints, tracing_on)
+ORIG_TRACING_ON=$(cat $TRACE/tracing_on 2>/dev/null || echo 0)
+ORIG_TP_SAMPLE=$(cat $TRACE/events/damon/damon_perf_sample/enable 2>/dev/null || echo 0)
+ORIG_TP_OVERFLOW=$(cat $TRACE/events/damon/damon_perf_ring_overflow/enable 2>/dev/null || echo 0)
+ORIG_TP_MISSED=$(cat $TRACE/events/damon/damon_perf_report_missed/enable 2>/dev/null || echo 0)
+ORIG_TP_DRAIN=$(cat $TRACE/events/damon/damon_perf_drain/enable 2>/dev/null || echo 0)
+
+cleanup() {
+ echo ""
+ echo "=== Cleaning up ==="
+ if [[ -n "$STRESS_PID" ]]; then
+ kill "$STRESS_PID" 2>/dev/null || true
+ wait "$STRESS_PID" 2>/dev/null || true
+ STRESS_PID=""
+ fi
+ # Tear down only the kdamond instance created by this test. In
+ # particular, the early "existing kdamonds" guard must be read-only.
+ if [[ "$CREATED_KDAMOND" == "1" ]]; then
+ echo off > $ADMIN/state 2>/dev/null || true
+ echo 0 > $KD/nr_kdamonds 2>/dev/null || true
+ CREATED_KDAMOND=0
+ fi
+ # Restore tracepoint and tracing state
+ echo 0 > $TRACE/tracing_on 2>/dev/null || true
+ echo "$ORIG_TP_SAMPLE" > $TRACE/events/damon/damon_perf_sample/enable 2>/dev/null || true
+ echo "$ORIG_TP_OVERFLOW" > $TPD/damon_perf_ring_overflow/enable 2>/dev/null || true
+ echo "$ORIG_TP_MISSED" > $TPD/damon_perf_report_missed/enable 2>/dev/null || true
+ echo "$ORIG_TP_DRAIN" > $TRACE/events/damon/damon_perf_drain/enable 2>/dev/null || true
+ echo "$ORIG_TRACING_ON" > $TRACE/tracing_on 2>/dev/null || true
+ if [[ "$MOUNTED_DEBUGFS" == "1" ]]; then
+ umount /sys/kernel/debug 2>/dev/null || true
+ MOUNTED_DEBUGFS=0
+ fi
+ [ "$KEEP_RESULTS" != "1" ] && rm -rf "$RESULTS_DIR"
+}
+trap cleanup EXIT
+
+# ---- argument parsing ----
+while [[ $# -gt 0 ]]; do
+ case "$1" in
+ --pmu) PMU_NAME="$2"; shift 2 ;;
+ --pmu-type) PMU_TYPE="$2"; shift 2 ;;
+ --config) PMU_CONFIG="$2"; CONFIG_EXPLICIT=1; shift 2 ;;
+ --freq) FREQ="$2"; FREQ_EXPLICIT=1; shift 2 ;;
+ --period) PERIOD="$2"; PERIOD_EXPLICIT=1; shift 2 ;;
+ --sample-freq) SAMPLE_FREQ="$2"; shift 2 ;;
+ --trace-window) TRACE_WINDOW="$2"; shift 2 ;;
+ --timeout) TIMEOUT="$2"; shift 2 ;;
+ --pid) TARGET_PID="$2"; shift 2 ;;
+ *) echo "Unknown: $1"; exit 1 ;;
+ esac
+done
+
+# Resolve PMU type
+if [[ -n "$PMU_NAME" && -z "$PMU_TYPE" ]]; then
+ if [[ "$PMU_NAME" == "software" ]]; then
+ PMU_TYPE=1
+ else
+ PMU_TYPE=$(cat /sys/bus/event_source/devices/$PMU_NAME/type 2>/dev/null) ||
+ die "Cannot find PMU: $PMU_NAME"
+ fi
+fi
+[[ -z "$PMU_TYPE" ]] && die "Specify --pmu <name> or --pmu-type <number>"
+
+# For PERF_TYPE_SOFTWARE default to PERF_COUNT_SW_PAGE_FAULTS (config 2):
+# the only software event that carries a data address, i.e. the only one
+# that can exercise Layers 5-7. Override with --config 0 for a pure
+# plumbing (cpu-clock) smoke test.
+if [[ "$PMU_TYPE" == "1" && "$CONFIG_EXPLICIT" == "0" ]]; then
+ PMU_CONFIG=2
+fi
+
+# For the page-fault positive control, sample every fault (period 1) by
+# default so enough reports flow for the ring/drain/match checks to be
+# meaningful on a short run. Explicit --freq/--period override this.
+if [[ "$PMU_TYPE" == "1" && "$PMU_CONFIG" == "2" &&
+ "$FREQ_EXPLICIT" == "0" && "$PERIOD_EXPLICIT" == "0" ]]; then
+ FREQ=0
+ PERIOD=1
+fi
+
+# For cpu-clock (config 0), sample_period is a TIME in ns, so the
+# default period 256 would mean 4 MHz of callbacks per CPU. Never
+# let an unguarded default hit that: fall back to a gentle 100 Hz.
+if [[ "$PMU_TYPE" == "1" && "$PMU_CONFIG" == "0" &&
+ "$FREQ_EXPLICIT" == "0" && "$PERIOD_EXPLICIT" == "0" ]]; then
+ FREQ=1
+ SAMPLE_FREQ=100
+fi
+
+# ---- Layer 0: Environment ----
+echo "=========================================="
+echo " DAMON Perf Observability — Layer-by-Layer Test"
+echo "=========================================="
+echo "PMU type: $PMU_TYPE config: $PMU_CONFIG freq: $FREQ period: $PERIOD timeout: ${TIMEOUT}s"
+if [[ -n "$TARGET_PID" ]]; then
+ echo "Target PID: $TARGET_PID (explicit)"
+else
+ echo "Target PID: workload process (started below)"
+fi
+echo ""
+
+mkdir -p "$RESULTS_DIR"
+
+echo "--- Layer 0: Environment ---"
+
+# Check kernel config
+CONFIG=""
+if [[ -f /proc/config.gz ]]; then
+ CONFIG=$(zcat /proc/config.gz)
+elif [[ -f /boot/config-$(uname -r) ]]; then
+ CONFIG=$(cat /boot/config-$(uname -r))
+else
+ die "Cannot read /proc/config.gz or /boot/config-$(uname -r)"
+fi
+
+for opt in DAMON DAMON_SYSFS DAMON_VADDR PERF_EVENTS DEBUG_FS TRACING \
+ TRACEPOINTS; do
+ if echo "$CONFIG" | grep -q "CONFIG_${opt}=y"; then
+ pass "CONFIG_${opt}=y"
+ else
+ fail "CONFIG_${opt}" "not enabled"
+ fi
+done
+
+# DAMON_PERF_OBSERVE is fatal — the test cannot run without it
+if echo "$CONFIG" | grep -q "CONFIG_DAMON_PERF_OBSERVE=y"; then
+ pass "CONFIG_DAMON_PERF_OBSERVE=y"
+else
+ die "kernel not built with CONFIG_DAMON_PERF_OBSERVE=y"
+fi
+
+# Check root
+[[ $(id -u) -eq 0 ]] || die "Must run as root"
+
+# Mount debugfs only when this test owns the mount, and undo it on exit.
+if ! mountpoint -q /sys/kernel/debug; then
+ mount -t debugfs none /sys/kernel/debug || die "Cannot mount debugfs"
+ MOUNTED_DEBUGFS=1
+fi
+[[ -d /sys/kernel/debug/damon ]] || die "debugfs damon/ not found"
+pass "debugfs mounted"
+
+# Check tracepoints
+for tp in damon_perf_sample damon_perf_ring_overflow damon_perf_report_missed damon_perf_drain; do
+ if [[ -d /sys/kernel/debug/tracing/events/damon/$tp ]]; then
+ pass "tracepoint $tp exists"
+ else
+ fail "tracepoint $tp" "not found"
+ fi
+done
+
+# Check debugfs file (perf_stats only; format is debug-only, not an ABI)
+if [[ -f /sys/kernel/debug/damon/perf_stats ]]; then
+ pass "debugfs perf_stats exists"
+else
+ fail "debugfs perf_stats" "not found"
+fi
+
+# ---- Guard: refuse to run if kdamonds already exist ----
+NR_KDAMONDS=$(cat $KD/nr_kdamonds 2>/dev/null || echo 0)
+if [[ "$NR_KDAMONDS" -gt 0 ]]; then
+ skip "runtime" "kdamonds exist (nr_kdamonds=$NR_KDAMONDS) — refusing"
+ KEEP_RESULTS=1
+ exit 0
+fi
+
+# ---- Generate memory pressure workload first: the default DAMON
+# ---- target must be the workload process itself, so the workload
+# ---- must be running before the target PID is written.
+echo ""
+echo "Starting memory workload for ${TIMEOUT}s..."
+if command -v stress-ng &>/dev/null; then
+ stress-ng --vm 2 --vm-bytes 256M --timeout "${TIMEOUT}s" &
+ STRESS_PID=$!
+elif command -v stress &>/dev/null; then
+ stress --vm 2 --vm-bytes 256M --timeout "${TIMEOUT}s" &
+ STRESS_PID=$!
+else
+ # Fallback: dd-based memory pressure
+ dd if=/dev/zero of=/dev/null bs=1M count=1024 &
+ STRESS_PID=$!
+fi
+
+# Resolve target PID: explicit --pid wins, otherwise the workload
+if [[ -z "$TARGET_PID" ]]; then
+ TARGET_PID=$STRESS_PID
+fi
+
+echo ""
+echo "--- Layer 1: Event Create ---"
+
+# Configure kdamond
+echo 1 > /sys/kernel/mm/damon/admin/kdamonds/nr_kdamonds
+CREATED_KDAMOND=1
+echo 1 > /sys/kernel/mm/damon/admin/kdamonds/0/contexts/nr_contexts
+echo 1 > /sys/kernel/mm/damon/admin/kdamonds/0/contexts/0/targets/nr_targets
+echo "$TARGET_PID" > /sys/kernel/mm/damon/admin/kdamonds/0/contexts/0/targets/0/pid_target
+
+# Disable page-fault-based access check
+echo 0 > $PE/nr_perf_events 2>/dev/null || true
+
+# Configure perf event
+echo 1 > $PE/nr_perf_events
+echo "$PMU_TYPE" > $PE/0/type
+echo "$PMU_CONFIG" > $PE/0/config
+
+if [[ "$FREQ" -eq 1 ]]; then
+ echo "$SAMPLE_FREQ" > $PE/0/sample_freq
+else
+ echo "$PERIOD" > $PE/0/sample_period
+fi
+echo "$FREQ" > $PE/0/freq
+
+# Take a dmesg snapshot before enabling the kdamond, so we can
+# detect error messages that appear during the test.
+DMESG_BEFORE="$RESULTS_DIR/dmesg_before.txt"
+dmesg > "$DMESG_BEFORE" 2>/dev/null || true
+# Snapshot counters BEFORE the workload window. All counters are
+# cumulative since boot; every Analysis number below is a delta against
+# this snapshot. Read before echo on so the window starts at zero.
+STATS_BASE="$RESULTS_DIR/perf_stats_base.txt"
+cat /sys/kernel/debug/damon/perf_stats > "$STATS_BASE" 2>/dev/null || true
+
+echo on > /sys/kernel/mm/damon/admin/kdamonds/0/state
+sleep 2
+
+DMESG_OUT="$RESULTS_DIR/dmesg_create.txt"
+DMESG_DELTA="$RESULTS_DIR/dmesg_delta.txt"
+dmesg > "$DMESG_OUT" 2>/dev/null || true
+# Delta: lines in $DMESG_OUT not already present in $DMESG_BEFORE
+awk 'NR==FNR { seen[$0]++ }
+ NR>FNR { if (seen[$0] > 0) seen[$0]--; else print }' \
+ "$DMESG_BEFORE" "$DMESG_OUT" > "$DMESG_DELTA" || true
+
+# Check state is on
+STATE_VAL=$(cat /sys/kernel/mm/damon/admin/kdamonds/0/state 2>/dev/null)
+if [[ "$STATE_VAL" == "on" ]]; then
+ pass "Kdamond state is on"
+else
+ fail "Kdamond state" "expected 'on', got '$STATE_VAL'"
+fi
+
+echo ""
+echo "--- Layer 2-3: Enable & Run (via per-CPU state) ---"
+
+# Parse the maximum per-CPU state from the debugfs output.
+# The per-CPU line format is:
+# CPU%02d: st=<state> cb=... enq=... ...
+max_cpu_state() {
+ awk -F'st=' '/^ CPU/ {
+ split($2, a, " ")
+ s = a[1]
+ # Map state name to numeric rank
+ if (s == "ERROR") v = 5
+ else if (s == "RUNNING") v = 4
+ else if (s == "ENABLED") v = 3
+ else if (s == "BOUND") v = 2
+ else if (s == "CREATED") v = 1
+ else v = 0
+ if (v > max) max = v
+ } END { print max+0 }' "$1" 2>/dev/null
+}
+
+CPU_ST_BASE=$(max_cpu_state "$STATS_BASE")
+
+if [[ "$CPU_ST_BASE" -ge 1 ]]; then
+ pass "Event Created (max per-CPU state >= CREATED)"
+else
+ fail "Event Created" "max per-CPU state is $CPU_ST_BASE"
+fi
+
+if [[ "$CPU_ST_BASE" -ge 2 ]]; then
+ pass "Event Bound (max per-CPU state >= BOUND)"
+else
+ fail "Event Bound" "max per-CPU state is $CPU_ST_BASE"
+fi
+
+if [[ "$CPU_ST_BASE" -ge 3 ]]; then
+ pass "Event Enabled (max per-CPU state >= ENABLED)"
+else
+ fail "Event Enabled" "max per-CPU state is $CPU_ST_BASE"
+fi
+
+# Check dmesg delta for errors (vaddr.c pr_warn_ratelimited paths)
+if grep -q 'damon-perf.*failed\|event create failed' "$DMESG_DELTA" 2>/dev/null; then
+ fail "Perf event" "perf event creation failed (see dmesg delta)"
+else
+ pass "Perf event creation (no errors in dmesg delta)"
+fi
+
+echo ""
+echo "--- Layer 4: Sampling (Callback) ---"
+
+# Clear the trace buffer so trace.txt only contains records produced by
+# this run, then enable tracepoints for a bounded sampling window.
+echo 0 > $TRACE/tracing_on 2>/dev/null || true
+echo > $TRACE/trace 2>/dev/null || true
+echo 1 > $TRACE/events/damon/damon_perf_sample/enable
+echo 1 > $TRACE/events/damon/damon_perf_ring_overflow/enable
+echo 1 > $TRACE/events/damon/damon_perf_report_missed/enable
+echo 1 > $TRACE/events/damon/damon_perf_drain/enable
+echo 1 > $TRACE/tracing_on
+
+# Sampling window: keeps trace.txt bounded even on PMUs that sample at
+# tens of kHz. Counters keep accumulating for the full TIMEOUT.
+sleep "$TRACE_WINDOW"
+echo 0 > $TRACE/tracing_on 2>/dev/null || true
+[[ "$TIMEOUT" -gt "$TRACE_WINDOW" ]] && sleep $((TIMEOUT - TRACE_WINDOW))
+
+kill $STRESS_PID 2>/dev/null || true
+wait $STRESS_PID 2>/dev/null || true
+STRESS_PID=""
+echo "Workload done."
+
+sleep 2 # let kdamond drain
+
+# Collect trace
+TRACE_OUT="$RESULTS_DIR/trace.txt"
+cat /sys/kernel/debug/tracing/trace > "$TRACE_OUT" 2>/dev/null || true
+TRACE_LINES=$(wc -l < "$TRACE_OUT" 2>/dev/null || echo 0)
+
+# Collect stats (re-read after workload)
+STATS_OUT="$RESULTS_DIR/perf_stats.txt"
+cat /sys/kernel/debug/damon/perf_stats > "$STATS_OUT" 2>/dev/null || true
+
+# ---- Analysis ----
+echo ""
+echo "--- Analysis ---"
+
+
+# Aggregate counter reads
+stat_of() {
+ awk -v k="$1" '$1==k {print $2}' "$2" 2>/dev/null
+}
+
+# Per-run delta between baseline and post-workload snapshots
+delta() {
+ local b a
+ b=$(stat_of "$1" "$STATS_BASE")
+ a=$(stat_of "$1" "$STATS_OUT")
+ [[ -z "$b" ]] && b=0
+ [[ -z "$a" ]] && a=0
+ echo $((a-b))
+}
+
+CALLBACK=$(delta callback)
+VALID=$(delta valid)
+ADDR_ZERO=$(delta addr_zero)
+KERNEL=$(delta kernel)
+ENQUEUE=$(delta enqueue)
+DEQUEUE=$(delta dequeue)
+OVERFLOW=$(delta overflow)
+MATCH=$(delta match)
+UPDATE=$(delta update)
+
+echo " Callback delta this run: ${CALLBACK} (cumulative totals in perf_stats.txt)"
+
+if [[ "$CALLBACK" -gt 0 ]]; then
+ pass "Sampling: ${CALLBACK} callbacks received"
+else
+ fail "Sampling" "0 callbacks — PMU is not delivering samples to DAMON"
+fi
+
+echo " Callback breakdown (delta): valid=${VALID} addr_zero=${ADDR_ZERO} kernel=${KERNEL}"
+
+# Verify RUNNING state: first callback advances per-CPU state to
+# RUNNING, which persists until the kdamond is stopped.
+CPU_ST_FINAL=$(max_cpu_state "$STATS_OUT")
+if [[ "$CALLBACK" -gt 0 && "$CPU_ST_FINAL" -ge 4 ]]; then
+ pass "Event Running (max per-CPU state >= RUNNING)"
+elif [[ "$CALLBACK" -eq 0 ]]; then
+ skip "Event Running" "no callbacks — state cannot advance past ENABLED"
+else
+ fail "Event Running" "callbacks > 0 but max state is $CPU_ST_FINAL"
+fi
+
+echo " Ring: enqueue=${ENQUEUE} dequeue=${DEQUEUE} overflow=${OVERFLOW}"
+
+if [[ "$ENQUEUE" -gt 0 ]]; then
+ pass "Ring: enqueue > 0"
+ if [[ "$DEQUEUE" -gt 0 ]]; then
+ pass "Ring: dequeue > 0"
+ else
+ fail "Ring: dequeue" "enqueued but never dequeued"
+ fi
+else
+ skip "Ring" "no enqueues (no valid samples: addr=0 or no callbacks)"
+fi
+
+echo " Match: match=${MATCH} update=${UPDATE}"
+
+if [[ "$MATCH" -gt 0 ]]; then
+ pass "Drain & Match: ${MATCH} matched"
+ if [[ "$UPDATE" -gt 0 ]]; then
+ pass "Update: ${UPDATE} region updates"
+ else
+ fail "Update" "matched but never updated"
+ fi
+else
+ skip "Match/Update" "no matches (no valid samples reached region matching)"
+fi
+
+# Drain tracepoint: kdamond fires damon_perf_drain whenever it drained
+# at least one report. The drain tracepoint is only expected when the
+# ring actually produced entries.
+DRAIN_COUNT=$(grep -c "damon_perf_drain" "$TRACE_OUT" 2>/dev/null || true)
+DRAIN_COUNT=${DRAIN_COUNT:-0}
+echo " Drain tracepoint: ${DRAIN_COUNT} records"
+if [[ "$MATCH" -gt 0 ]]; then
+ if [[ "$DRAIN_COUNT" -gt 0 ]]; then
+ pass "Drain tracepoint fired (${DRAIN_COUNT} records)"
+ else
+ fail "Drain tracepoint" "matches occurred but damon_perf_drain never fired"
+ fi
+else
+ skip "Drain tracepoint" "no drained reports to summarize"
+fi
+
+# Context verification
+if grep -q 'context=' "$TRACE_OUT" 2>/dev/null; then
+ NMI_COUNT=$(grep -c 'context=3' "$TRACE_OUT" 2>/dev/null || true)
+ PROC_COUNT=$(grep -c 'context=0' "$TRACE_OUT" 2>/dev/null || true)
+ NMI_COUNT=${NMI_COUNT:-0}
+ PROC_COUNT=${PROC_COUNT:-0}
+ echo " Context: NMI=${NMI_COUNT} process=${PROC_COUNT}"
+ pass "Context field in trace output"
+else
+ skip "Context" "no trace output to analyze"
+fi
+
+# Show a few sample records as raw evidence (they are the per-sample
+# view of the pipeline; useful for PMU support evaluation).
+echo ""
+echo " First damon_perf_sample record(s) this run:"
+if grep -q "damon_perf_sample" "$TRACE_OUT" 2>/dev/null; then
+ grep -m 3 "damon_perf_sample" "$TRACE_OUT" | sed 's/^/ /'
+else
+ echo " (none — no samples captured in the ${TRACE_WINDOW}s window)"
+fi
+echo " First damon_perf_drain record(s) this run:"
+if grep -q "damon_perf_drain" "$TRACE_OUT" 2>/dev/null; then
+ grep -m 3 "damon_perf_drain" "$TRACE_OUT" | sed 's/^/ /'
+else
+ echo " (none)"
+fi
+
+# ---- PMU support verdict ----
+echo ""
+echo "--- PMU support verdict ---"
+if [[ "$CALLBACK" -eq 0 ]]; then
+ echo " UNUSABLE: the PMU never delivered a sample to DAMON"
+ echo " (e.g. ARM SPE requires an AUX ring buffer that kernel"
+ echo " counters do not provide; see arm_spe_pmu.c)"
+elif [[ "$VALID" -eq 0 ]]; then
+ echo " PLUMBING-ONLY: callbacks flow but no data addresses"
+ echo " (address-less PMU, e.g. cpu-clock / task-clock)"
+elif [[ "$ENQUEUE" -gt 0 && "$MATCH" -gt 0 ]]; then
+ echo " FULLY INTEGRATED: samples carry addresses and reach"
+ echo " DAMON region matching/update"
+else
+ echo " PARTIAL: callbacks with addresses, but the drain/match"
+ echo " pipeline did not complete (see counters above)"
+fi
+
+# ---- Summary ----
+echo ""
+echo "=========================================="
+echo " SUMMARY: $PASSED passed, $FAILED failed, $SKIPPED skipped"
+echo "=========================================="
+echo ""
+echo "Results retained in: $RESULTS_DIR (set KEEP_RESULTS=0 to remove)"
+
+if [[ "$FAILED" -gt 0 ]]; then
+ echo "Overall: FAIL ($FAILED checks failed)"
+ exit 1
+else
+ echo "Overall: PASS"
+ exit 0
+fi
--
2.43.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [RFC PATCH 6/7] Docs/mm/damon: document the perf observability framework
2026-08-18 6:10 [RFC PATCH 0/7] mm/damon/perf: observability framework for hardware-sampled access reports Kunwu Chan
` (4 preceding siblings ...)
2026-08-18 6:10 ` [RFC PATCH 5/7] selftests/damon: add automated layer-by-layer observability test Kunwu Chan
@ 2026-08-18 6:10 ` Kunwu Chan
2026-08-18 6:10 ` [RFC PATCH 7/7] mm/damon/perf: add CONFIG_DAMON_PERF_DEBUG and pipeline health check Kunwu Chan
6 siblings, 0 replies; 8+ messages in thread
From: Kunwu Chan @ 2026-08-18 6:10 UTC (permalink / raw)
To: sj, akpm
Cc: damon, linux-mm, linux-kernel, linux-trace-kernel,
linux-kselftest, rostedt, mhiramat, mathieu.desnoyers, shuah,
lianux.mm, Kunwu Chan
From: Lian Wang <lianux.mm@gmail.com>
Add documentation for the DAMON perf observability framework,
covering the CONFIG_DAMON_PERF_OBSERVE Kconfig option, the
debugfs perf_stats interface, the tracepoints, and the per-CPU
pipeline counter model. The debugfs format is explicitly marked
as unstable and must not be used by scripts.
Co-developed-by: Kunwu Chan <kunwu.chan@gmail.com>
Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
Signed-off-by: Lian Wang <lianux.mm@gmail.com>
---
Documentation/admin-guide/mm/damon/index.rst | 1 +
.../mm/damon/perf-observability.rst | 210 ++++++++++++++++++
2 files changed, 211 insertions(+)
create mode 100644 Documentation/admin-guide/mm/damon/perf-observability.rst
diff --git a/Documentation/admin-guide/mm/damon/index.rst b/Documentation/admin-guide/mm/damon/index.rst
index 3ce3164480c7..623a5c312b69 100644
--- a/Documentation/admin-guide/mm/damon/index.rst
+++ b/Documentation/admin-guide/mm/damon/index.rst
@@ -15,3 +15,4 @@ access monitoring and access-aware system operations.
reclaim
lru_sort
stat
+ perf-observability
diff --git a/Documentation/admin-guide/mm/damon/perf-observability.rst b/Documentation/admin-guide/mm/damon/perf-observability.rst
new file mode 100644
index 000000000000..3aa8185de314
--- /dev/null
+++ b/Documentation/admin-guide/mm/damon/perf-observability.rst
@@ -0,0 +1,210 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=============================================
+DAMON Perf Event Observability Framework
+=============================================
+
+The DAMON perf event observability framework provides per-CPU counters and
+tracepoints for hardware-sampled access reports. When DAMON is configured to
+use a hardware PMU (e.g. AMD IBS, Intel PEBS, or ARM SPE) instead of page-table
+walks, this framework exposes raw pipeline diagnostics so that every stage of
+the PMU-to-DAMON pipeline can be inspected.
+
+Counters are best-effort: individual ``u64`` writes are atomic on 64-bit
+platforms, but no cross-field consistency is guaranteed. Do not build
+policy on snapshot reads. For stable, structured diagnostics, use the
+tracepoints under ``/sys/kernel/debug/tracing/events/damon/``.
+
+Pipeline Stages
+===============
+
+::
+
+ PMU hardware → overflow_handler / AUX drain
+ → damon_report_access() → per-CPU SPSC ring
+ → kdamond drain → target match → region update
+
+ Layer 1: Event Create perf_event_create_kernel_counter()
+ Layer 2: Event Bind per-CPU PMU attachment
+ Layer 3: Event Enable perf_event_enable()
+ Layer 4: Sampling callback / AUX record received
+ Layer 5: Ring SPSC enqueue / dequeue / overflow
+ Layer 6: Drain kdamond consumes entries from ring
+ Layer 7: Match & Update region access-rate update
+
+Each layer has a dedicated counter, and most layers have corresponding
+tracepoints. Per-CPU event state (UNINIT → CREATED → BOUND → ENABLED →
+RUNNING) is recorded unconditionally and exposed via the debugfs
+perf_stats file.
+
+Overhead Control
+================
+
+Two levels of overhead control are provided:
+
+1. **Compile-time** — ``CONFIG_DAMON_PERF_OBSERVE``
+ When set to ``n``, all observe functions are compiled to static-inline
+ no-ops. No code is generated and no runtime overhead exists.
+
+2. **Per-tracepoint on/off** — standard ftrace ``enable`` files
+ Individual tracepoints (``damon_perf_sample``, etc.) can be
+ enabled or disabled independently via
+ ``/sys/kernel/debug/tracing/events/damon/``. Counter increments are
+ unconditional (cheap per-CPU ``inc``); tracepoint decisions are
+ guarded by the ftrace static key and are zero-overhead when disabled.
+
+When ``CONFIG_DAMON_PERF_OBSERVE=y``, per-CPU counters always increment.
+There is no runtime toggle for counters; compile-time is the sole gate.
+
+Debugfs Interface
+=================
+
+Mount debugfs::
+
+ # mount -t debugfs none /sys/kernel/debug
+
+One file is created under ``/sys/kernel/debug/damon/``:
+
+perf_stats
+----------
+
+**DEBUG ONLY — format may change without notice.** Do not parse in
+scripts or tools. For stable diagnostics, use the tracepoints.
+
+Read-only. Aggregated counter table with all pipeline counters plus
+per-CPU breakdown::
+
+ # cat /sys/kernel/debug/damon/perf_stats
+ ┌──────────────┬──────────┐
+ │ Counter │ Value │
+ ├──────────────┼──────────┤
+ │ callback │ 233 │
+ │ valid │ 0 │
+ │ null │ 0 │
+ │ addr_zero │ 233 │
+ │ kernel │ 0 │
+ │ inv_phys │ 0 │
+ │ enqueue │ 0 │
+ │ dequeue │ 0 │
+ │ overflow │ 0 │
+ │ ring_peak │ 0 │
+ │ match │ 0 │
+ │ miss_tgid │ 0 │
+ │ miss_region │ 0 │
+ │ miss_bound │ 0 │
+ │ update │ 0 │
+ └──────────────┴──────────┘
+
+ Per-CPU (non-zero / non-UNINIT):
+ CPU00: st=BOUND cb=44 enq=0 deq=0 ovf=0 match=0 miss=0 upd=0
+ ...
+
+The ``st=<state>`` column shows the per-CPU event state machine position
+(UNINIT, CREATED, BOUND, ENABLED, RUNNING, ERROR), derived from the
+lifecycle observe calls. This allows verifying lifecycle progression
+without parsing dmesg.
+
+All counters are monotonic (cumulative since boot); userspace computes
+deltas between snapshots.
+
+Tracepoints
+===========
+
+Four tracepoints are defined::
+
+ damon_perf_sample
+ damon_perf_ring_overflow
+ damon_perf_report_missed
+ damon_perf_drain
+
+Enable via ftrace::
+
+ # echo 1 > /sys/kernel/debug/tracing/events/damon/damon_perf_sample/enable
+ # cat /sys/kernel/debug/tracing/trace_pipe
+
+Each ``damon_perf_sample`` record includes:
+
+ - ``addr``: the accessed virtual address (0 if the PMU did not populate)
+ - ``data_src``: PERF_MEM_* encoding (PMU-dependent)
+ - ``period``: sample period or frequency count
+ - ``cpu``: CPU that generated the sample
+ - ``reason``: 0=valid, 1=null-data, 2=addr-zero, 3=kernel-addr, 4=invalid-phys
+ - ``sample_flags``: what the PMU actually populated
+ - ``sample_type``: what DAMON requested
+ - ``context``: 0=process, 1=softirq, 2=hardirq, 3=NMI
+
+The ``context`` field is particularly useful for cross-PMU validation.
+For example, AMD IBS samples arrive in NMI context (context=3), while
+ARM SPE data from an AUX backend would arrive in process context (context=0).
+A mismatch between the expected and actual context is immediately visible.
+
+Selftest
+========
+
+A comprehensive automated test script is provided::
+
+ # cd tools/testing/selftests/damon
+ # sudo ./damon_perf_obs_test.sh --pmu arm_spe_0 --freq 0 --period 256
+
+The script performs a layer-by-layer validation:
+
+1. Checks kernel configuration (CONFIG_DAMON, CONFIG_DAMON_PERF_OBSERVE, etc.)
+2. Verifies PMU availability, tracepoints, and the debugfs perf_stats file
+3. Refuses to run if existing kdamonds are present (side-effect guard)
+4. Configures DAMON with the specified PMU via sysfs
+5. Runs a memory workload (stress-ng, stress, or dd fallback)
+6. Collects dmesg delta, trace output, and perf_stats
+7. Verifies per-CPU state progression and counter values
+
+Example output::
+
+ --- Layer 0: Environment ---
+ [PASS] CONFIG_DAMON_PERF_OBSERVE=y
+ [PASS] debugfs perf_stats exists
+
+ --- Layer 2-3: Enable & Run (via per-CPU state) ---
+ [PASS] Event Created (max per-CPU state >= CREATED)
+ [PASS] Event Bound (max per-CPU state >= BOUND)
+ [PASS] Event Enabled (max per-CPU state >= ENABLED)
+
+ --- Layer 4: Sampling (Callback) ---
+ [PASS] Sampling: 84532 callbacks received
+ Callback breakdown: valid=82103 addr_zero=0 kernel=2429
+
+ --- Layer 5: Ring ---
+ [PASS] Ring: enqueue > 0
+ [PASS] Ring: dequeue > 0
+ Ring: enqueue=82100 dequeue=81987 overflow=0
+
+ --- Layer 6: Drain & Match ---
+ [PASS] Drain & Match: 81987 matched
+ [PASS] Update: 81987 region updates
+
+Additional PMU examples::
+
+ # Software page-fault event (positive control):
+ sudo ./damon_perf_obs_test.sh --pmu software --freq 1 --sample-freq 100
+
+ # Any PMU by type number:
+ sudo ./damon_perf_obs_test.sh --pmu-type 38 --freq 0 --period 256
+
+Kernel Configuration
+====================
+
+Required for observability::
+
+ CONFIG_DAMON=y
+ CONFIG_DAMON_SYSFS=y
+ CONFIG_DAMON_VADDR=y
+ CONFIG_PERF_EVENTS=y
+ CONFIG_DEBUG_FS=y
+ CONFIG_TRACING=y
+ CONFIG_TRACEPOINTS=y
+
+Optional (enables observability framework)::
+
+ CONFIG_DAMON_PERF_OBSERVE=y
+
+When ``CONFIG_DAMON_PERF_OBSERVE=n``, ``/sys/kernel/debug/damon/perf_stats``
+is not created, tracepoints are not registered, and all observe functions
+are compiled to empty static inlines with zero overhead.
--
2.43.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [RFC PATCH 7/7] mm/damon/perf: add CONFIG_DAMON_PERF_DEBUG and pipeline health check
2026-08-18 6:10 [RFC PATCH 0/7] mm/damon/perf: observability framework for hardware-sampled access reports Kunwu Chan
` (5 preceding siblings ...)
2026-08-18 6:10 ` [RFC PATCH 6/7] Docs/mm/damon: document the perf observability framework Kunwu Chan
@ 2026-08-18 6:10 ` Kunwu Chan
6 siblings, 0 replies; 8+ messages in thread
From: Kunwu Chan @ 2026-08-18 6:10 UTC (permalink / raw)
To: sj, akpm
Cc: damon, linux-mm, linux-kernel, linux-trace-kernel,
linux-kselftest, rostedt, mhiramat, mathieu.desnoyers, shuah,
lianux.mm, Kunwu Chan
From: Lian Wang <lianux.mm@gmail.com>
Add CONFIG_DAMON_PERF_DEBUG as an optional Kconfig option that
enables pr_debug() output for the observability pipeline via the
damon_perf_dbg() macro. Default off, zero overhead when disabled.
Add a pipeline health check to the observability selftest that
diagnoses which stage is broken when callbacks are zero, using the
existing per-CPU state and counter deltas.
Co-developed-by: Kunwu Chan <kunwu.chan@gmail.com>
Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
Signed-off-by: Lian Wang <lianux.mm@gmail.com>
---
mm/damon/Kconfig | 16 ++++++++++++++++
mm/damon/perf/debugfs.c | 5 ++++-
mm/damon/perf/perf.h | 7 +++++++
mm/damon/perf/stats.c | 15 ++++++++++++++-
.../selftests/damon/damon_perf_obs_test.sh | 18 +++++++++++++++++-
5 files changed, 58 insertions(+), 3 deletions(-)
diff --git a/mm/damon/Kconfig b/mm/damon/Kconfig
index 9f811510760f..35ec4d12c5b8 100644
--- a/mm/damon/Kconfig
+++ b/mm/damon/Kconfig
@@ -148,4 +148,20 @@ config DAMON_PERF_OBSERVE
static-inline no-ops with zero runtime overhead.
If unsure, say N.
+
+config DAMON_PERF_DEBUG
+ bool "DAMON Perf verbose debugging output"
+ depends on DAMON_PERF_OBSERVE
+ help
+ Enable verbose per-event and per-drain pr_debug() output
+ for the DAMON perf observability pipeline. When enabled,
+ key lifecycle transitions and sampling events are logged
+ at KERN_DEBUG level, visible via dynamic_debug or when
+ DEBUG is defined at compile time.
+
+ This adds dmesg noise and should only be enabled for
+ development or troubleshooting.
+
+ If unsure, say N.
+
endmenu
diff --git a/mm/damon/perf/debugfs.c b/mm/damon/perf/debugfs.c
index c54dd7644ac3..48f3d23c2dbc 100644
--- a/mm/damon/perf/debugfs.c
+++ b/mm/damon/perf/debugfs.c
@@ -132,11 +132,14 @@ int damon_perf_debugfs_init(void)
damon_debugfs_dir = debugfs_create_dir("damon", NULL);
if (damon_debugfs_dir == ERR_PTR(-EEXIST))
damon_debugfs_dir = debugfs_lookup("damon", NULL);
- if (IS_ERR(damon_debugfs_dir))
+ if (IS_ERR(damon_debugfs_dir)) {
+ damon_perf_dbg("debugfs init failed: %ld\n", PTR_ERR(damon_debugfs_dir));
return PTR_ERR(damon_debugfs_dir);
+ }
debugfs_create_file("perf_stats", 0400, damon_debugfs_dir,
NULL, &perf_stats_fops);
+ damon_perf_dbg("debugfs init ok\n");
return 0;
}
diff --git a/mm/damon/perf/perf.h b/mm/damon/perf/perf.h
index 78e23d436336..908c06f2e3db 100644
--- a/mm/damon/perf/perf.h
+++ b/mm/damon/perf/perf.h
@@ -18,6 +18,13 @@
struct perf_event;
#include <linux/types.h>
+#ifdef CONFIG_DAMON_PERF_DEBUG
+#define damon_perf_dbg(fmt, ...) \
+ pr_debug("damon-perf: " fmt, ##__VA_ARGS__)
+#else
+#define damon_perf_dbg(fmt, ...) no_printk(fmt, ##__VA_ARGS__)
+#endif
+
struct damon_perf_event;
/*
diff --git a/mm/damon/perf/stats.c b/mm/damon/perf/stats.c
index ae5b0037a31d..e2c1e5764d41 100644
--- a/mm/damon/perf/stats.c
+++ b/mm/damon/perf/stats.c
@@ -67,6 +67,7 @@ void damon_perf_observe_event_created(struct damon_perf_event *event, int cpu)
return;
}
*per_cpu_ptr(event->cpu_state, cpu) = DAMON_PERF_STATE_CREATED;
+ damon_perf_dbg("cpu %d: event created\n", cpu);
damon_perf_cpu_state_advance(cpu, DAMON_PERF_STATE_CREATED);
}
@@ -76,6 +77,7 @@ void damon_perf_observe_event_bound(struct damon_perf_event *event,
if (event->cpu_state)
*per_cpu_ptr(event->cpu_state, cpu) = DAMON_PERF_STATE_BOUND;
damon_perf_cpu_state_advance(cpu, DAMON_PERF_STATE_BOUND);
+ damon_perf_dbg("cpu %d: event bound\n", cpu);
}
void damon_perf_observe_event_enabled(struct damon_perf_event *event,
@@ -84,12 +86,14 @@ void damon_perf_observe_event_enabled(struct damon_perf_event *event,
if (event->cpu_state)
*per_cpu_ptr(event->cpu_state, cpu) = DAMON_PERF_STATE_ENABLED;
damon_perf_cpu_state_advance(cpu, DAMON_PERF_STATE_ENABLED);
+ damon_perf_dbg("cpu %d: event enabled\n", cpu);
}
void damon_perf_observe_event_disabled(struct damon_perf_event *event,
int cpu, int state)
{
/* State unchanged: the event may be re-enabled later. */
+ damon_perf_dbg("cpu %d: event disabled\n", cpu);
}
void damon_perf_observe_event_destroyed(struct damon_perf_event *event, int cpu)
@@ -104,6 +108,7 @@ void damon_perf_observe_event_destroyed(struct damon_perf_event *event, int cpu)
*/
if (event->cpu_state)
*per_cpu_ptr(event->cpu_state, cpu) = DAMON_PERF_STATE_UNINIT;
+ damon_perf_dbg("cpu %d: event destroyed\n", cpu);
}
void damon_perf_observe_event_free(struct damon_perf_event *event)
@@ -111,6 +116,7 @@ void damon_perf_observe_event_free(struct damon_perf_event *event)
if (event->cpu_state) {
free_percpu(event->cpu_state);
event->cpu_state = NULL;
+ damon_perf_dbg("event freed\n");
}
}
@@ -231,6 +237,7 @@ void damon_perf_observe_drain(unsigned int total, unsigned int matched)
{
if (trace_damon_perf_drain_enabled())
trace_damon_perf_drain(total, matched);
+ damon_perf_dbg("drain: total=%u matched=%u\n", total, matched);
}
/*
@@ -291,5 +298,11 @@ void damon_perf_stats_aggregate(struct damon_perf_stats *dst)
int damon_perf_framework_init(void)
{
- return damon_perf_debugfs_init();
+ int ret = damon_perf_debugfs_init();
+
+ if (ret)
+ damon_perf_dbg("framework init failed: %d\n", ret);
+ else
+ damon_perf_dbg("framework init ok\n");
+ return ret;
}
diff --git a/tools/testing/selftests/damon/damon_perf_obs_test.sh b/tools/testing/selftests/damon/damon_perf_obs_test.sh
index 4c4074cdd191..cd567c151ae6 100755
--- a/tools/testing/selftests/damon/damon_perf_obs_test.sh
+++ b/tools/testing/selftests/damon/damon_perf_obs_test.sh
@@ -344,7 +344,7 @@ max_cpu_state() {
} END { print max+0 }' "$1" 2>/dev/null
}
-CPU_ST_BASE=$(max_cpu_state "$STATS_BASE")
+CPU_ST_BASE=$(max_cpu_state /sys/kernel/debug/damon/perf_stats)
if [[ "$CPU_ST_BASE" -ge 1 ]]; then
pass "Event Created (max per-CPU state >= CREATED)"
@@ -431,6 +431,22 @@ VALID=$(delta valid)
ADDR_ZERO=$(delta addr_zero)
KERNEL=$(delta kernel)
ENQUEUE=$(delta enqueue)
+# Pipeline health check: diagnose which stage is broken when
+# callbacks are zero, using the existing per-CPU state and
+# counter deltas. This is a best-effort diagnostic, not a
+# substitute for detailed per-backend debugging.
+if [[ "$CALLBACK" -eq 0 ]]; then
+ CPU_ST_BASE_VAL=$(max_cpu_state /sys/kernel/debug/damon/perf_stats)
+ if [[ "$CPU_ST_BASE_VAL" -le 1 ]]; then
+ echo " Pipeline diagnosis: event not created or bound (state=$CPU_ST_BASE_VAL)"
+ elif [[ "$CPU_ST_BASE_VAL" -eq 2 ]]; then
+ echo " Pipeline diagnosis: event bound but not enabled (state=BOUND)"
+ elif [[ "$ENQUEUE" -eq 0 ]]; then
+ echo " Pipeline diagnosis: PMU not producing data or AUX pipeline broken"
+ else
+ echo " Pipeline diagnosis: samples enqueued but none valid"
+ fi
+fi
DEQUEUE=$(delta dequeue)
OVERFLOW=$(delta overflow)
MATCH=$(delta match)
--
2.43.0
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