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Fri, 06 Nov 2026 21:52:27 -0800 (PST) Received: from lipengfei28-ThinkStation-P368.mioffice.cn ([2408:8607:1b00:8:a1a:7bc2:20ba:a479]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ed47d8949fsm11189465ad.62.2026.11.06.21.52.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Nov 2026 21:52:26 -0800 (PST) From: Li Pengfei X-Google-Original-From: Li Pengfei To: rostedt@goodmis.org, mhiramat@kernel.org Cc: mathieu.desnoyers@efficios.com, mark.rutland@arm.com, corbet@lwn.net, skhan@linuxfoundation.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, zhangbo56@xiaomi.com, lipengfei28@xiaomi.com, lkp@intel.com Subject: [PATCH v8 3/5] tracing: Add stackmap statistics interface Date: Sat, 7 Nov 2026 13:51:37 +0800 Message-Id: <20261107055139.3138633-4-lipengfei28@xiaomi.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20261107055139.3138633-1-lipengfei28@xiaomi.com> References: <20261107055139.3138633-1-lipengfei28@xiaomi.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Pengfei Li Add stack_map_stat to report the map generation, the elements used, the stacks recorded as a cookie, and the stacks the map could not store because the element pool or the probe limit was exhausted, so that users can tell when the map is too small. Assisted-by: LLM Signed-off-by: Pengfei Li --- kernel/trace/trace.c | 4 ++ kernel/trace/trace_stackmap.c | 78 +++++++++++++++++++++++++++++++++++ kernel/trace/trace_stackmap.h | 1 + 3 files changed, 83 insertions(+) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index cdae2976d224..e58e7936c867 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2197,6 +2197,9 @@ static __init void stackmap_init_tracefs(void) return; } + trace_create_file("stack_map_stat", TRACE_MODE_READ, NULL, + &global_trace, &ftrace_stackmap_stat_fops); + guard(mutex)(&trace_types_lock); stackmap_state = STACKMAP_INIT_READY; /* trace_options=stackmap on the command line */ @@ -4399,6 +4402,7 @@ static const char readme_msg[] = #ifdef CONFIG_FTRACE_STACKMAP " stack_map\t\t- Stacks recorded as cookies with options/stackmap\n" "\t\t\t Write '0' to reset it, 'free' to release it\n" + " stack_map_stat\t- Usage of the stack map\n" #endif #ifdef CONFIG_DYNAMIC_EVENTS " dynamic_events\t\t- Create/append/remove/show the generic dynamic events\n" diff --git a/kernel/trace/trace_stackmap.c b/kernel/trace/trace_stackmap.c index b02eb22c76a9..5d2a406f39b9 100644 --- a/kernel/trace/trace_stackmap.c +++ b/kernel/trace/trace_stackmap.c @@ -42,6 +42,8 @@ struct ftrace_stackmap { atomic_t resetting; u32 generation; refcount_t ref; + atomic_long_t __percpu *successes; + atomic_long_t __percpu *fallbacks; }; /* Serializes tracefs readers against reset. */ @@ -73,6 +75,8 @@ static struct stackmap_elt *stackmap_get_elt(struct ftrace_stackmap *smap) static void ftrace_stackmap_destroy(struct ftrace_stackmap *smap) { + free_percpu(smap->fallbacks); + free_percpu(smap->successes); vfree(smap->elts); vfree(smap->entries); kfree(smap); @@ -100,6 +104,14 @@ static struct ftrace_stackmap *ftrace_stackmap_create(void) if (!smap->elts) goto fail; + smap->successes = alloc_percpu(atomic_long_t); + if (!smap->successes) + goto fail; + + smap->fallbacks = alloc_percpu(atomic_long_t); + if (!smap->fallbacks) + goto fail; + smap->hash_seed = get_random_u32(); smap->generation = stackmap_next_gen; refcount_set(&smap->ref, 1); @@ -149,6 +161,7 @@ static void stackmap_put(struct ftrace_stackmap *smap) static void stackmap_reset(struct trace_array *tr) { struct ftrace_stackmap *smap = stackmap_locked(tr); + int cpu; if (!smap) return; @@ -161,6 +174,10 @@ static void stackmap_reset(struct trace_array *tr) memset(smap->entries, 0, sizeof(*smap->entries) * smap->map_size); memset(smap->elts, 0, sizeof(*smap->elts) * smap->max_elts); atomic_set(&smap->next_elt, 0); + for_each_possible_cpu(cpu) { + atomic_long_set(per_cpu_ptr(smap->successes, cpu), 0); + atomic_long_set(per_cpu_ptr(smap->fallbacks, cpu), 0); + } smap->generation++; } @@ -194,6 +211,11 @@ static int stackmap_free(struct trace_array *tr, struct ftrace_stackmap *self) return ret; } +static void stackmap_count(atomic_long_t __percpu *counter) +{ + atomic_long_add_unless(this_cpu_ptr(counter), 1, LONG_MAX); +} + bool ftrace_stackmap_get_cookie(struct ftrace_stackmap *smap, unsigned long *ips, unsigned int nr_entries, u64 *cookie) @@ -254,8 +276,10 @@ bool ftrace_stackmap_get_cookie(struct ftrace_stackmap *smap, probes++; } + stackmap_count(smap->fallbacks); return false; found: + stackmap_count(smap->successes); *cookie = ((u64)smap->generation << FTRACE_STACKMAP_COOKIE_GEN_SHIFT) | idx; return true; } @@ -415,3 +439,57 @@ const struct file_operations ftrace_stackmap_fops = { .llseek = seq_lseek, .release = stackmap_release, }; + +static int stackmap_stat_show(struct seq_file *m, void *v) +{ + struct trace_array *tr = m->private; + struct ftrace_stackmap *smap; + u64 successes = 0, fallbacks = 0; + int cpu; + + /* Reset and free also take trace_types_lock. */ + guard(mutex)(&trace_types_lock); + smap = stackmap_locked(tr); + if (!smap) + return 0; + + for_each_possible_cpu(cpu) { + successes += atomic_long_read(per_cpu_ptr(smap->successes, cpu)); + fallbacks += atomic_long_read(per_cpu_ptr(smap->fallbacks, cpu)); + } + + seq_printf(m, "generation: %u\n", smap->generation); + seq_printf(m, "entries: %d\n", atomic_read(&smap->next_elt)); + seq_printf(m, "capacity: %u\n", smap->max_elts); + seq_printf(m, "successes: %llu\n", successes); + seq_printf(m, "fallbacks: %llu\n", fallbacks); + return 0; +} + +static int stackmap_stat_open(struct inode *inode, struct file *file) +{ + struct trace_array *tr = inode->i_private; + int ret; + + ret = tracing_check_open_get_tr(tr); + if (ret) + return ret; + + ret = single_open(file, stackmap_stat_show, tr); + if (ret) + trace_array_put(tr); + return ret; +} + +static int stackmap_stat_release(struct inode *inode, struct file *file) +{ + trace_array_put(inode->i_private); + return single_release(inode, file); +} + +const struct file_operations ftrace_stackmap_stat_fops = { + .open = stackmap_stat_open, + .read = seq_read, + .llseek = seq_lseek, + .release = stackmap_stat_release, +}; diff --git a/kernel/trace/trace_stackmap.h b/kernel/trace/trace_stackmap.h index 6699988da390..a18e41c08494 100644 --- a/kernel/trace/trace_stackmap.h +++ b/kernel/trace/trace_stackmap.h @@ -18,5 +18,6 @@ bool ftrace_stackmap_get_cookie(struct ftrace_stackmap *smap, u64 *cookie); extern const struct file_operations ftrace_stackmap_fops; +extern const struct file_operations ftrace_stackmap_stat_fops; #endif /* _TRACE_STACKMAP_H */ -- 2.34.1