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Mon, 17 Aug 2026 23:11:30 -0700 (PDT) From: Kunwu Chan X-Google-Original-From: Kunwu Chan To: sj@kernel.org, akpm@linux-foundation.org Cc: damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, shuah@kernel.org, lianux.mm@gmail.com, Kunwu Chan Subject: [RFC PATCH 7/7] mm/damon/perf: add CONFIG_DAMON_PERF_DEBUG and pipeline health check Date: Tue, 18 Aug 2026 14:10:31 +0800 Message-ID: <20260818061031.827057-8-kunwu.chan@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260818061031.827057-1-kunwu.chan@linux.dev> References: <20260818061031.827057-1-kunwu.chan@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Lian Wang 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 Signed-off-by: Kunwu Chan Signed-off-by: Lian Wang --- 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 +#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