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[67.174.206.244]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-71b26524c32sm1998410b3a.157.2024.09.27.13.27.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Sep 2024 13:27:55 -0700 (PDT) From: Howard Chu To: peterz@infradead.org Cc: mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, Howard Chu Subject: [PATCH v6 4/8] perf record off-cpu: Dump direct off-cpu samples in BPF Date: Fri, 27 Sep 2024 13:27:32 -0700 Message-ID: <20240927202736.767941-5-howardchu95@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240927202736.767941-1-howardchu95@gmail.com> References: <20240927202736.767941-1-howardchu95@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Add perf_event_array map for dumping direct off-cpu samples, but keep the at-the-end approach. Tons of checking before access, to pass the BPF verifier. If off-cpu time (represented as delta) exceeds the off-cpu threshold, do output. Output PERF_SAMPLE_TID, PERF_SAMPLE_PERIOD, PERF_SAMPLE_CALLCHAIN, and PERF_SAMPLE_CGROUP in bpf_perf_event_output(). Ideally, we should only output PERF_SAMPLE_PERIOD (off-cpu time) and PERF_SAMPLE_CALLCHAIN (sched_in process's callchain). One only needs to set PERF_SAMPLE_TID and PERF_SAMPLE_CGROUP, and perf_event will do everything for us. But in reality, that's not the case. Setting PERF_SAMPLE_TID will mostly give us TID of 0. We might get the correct TID for offcpu-time event from time to time, but it is really rare. swapper 0 [000] offcpu-time: / :1321819 1321819 [002] offcpu-time: /user.slice/user-1000.slice/se= ssion-2.scope swapper 0 [001] offcpu-time: / swapper 0 [003] offcpu-time: / And setting PERF_SAMPLE_CGROUP doesn't work properly either. tmux: server 3701 [003] offcpu-time: / blueman-tray 1064 [001] offcpu-time: / bash 1350867 [001] offcpu-time: / bash 1350844 [000] offcpu-time: / We need to retrieve PERF_SAMPLE_TID, PERF_SAMPLE_PERIOD, PERF_SAMPLE_CALLCHAIN, and PERF_SAMPLE_CGROUP using BPF and output these four fields. Suggested-by: Namhyung Kim Signed-off-by: Howard Chu --- tools/perf/util/bpf_skel/off_cpu.bpf.c | 112 +++++++++++++++++++++++++ tools/perf/util/off_cpu.h | 8 +- 2 files changed, 119 insertions(+), 1 deletion(-) diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_s= kel/off_cpu.bpf.c index e2a887228fd9..c42d0e2d91d8 100644 --- a/tools/perf/util/bpf_skel/off_cpu.bpf.c +++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c @@ -19,6 +19,7 @@ #define MAX_ENTRIES 102400 =20 #define MAX_CPUS 4096 +#define MAX_OFFCPU_LEN 128 =20 struct tstamp_data { __u32 stack_id; @@ -34,6 +35,7 @@ struct offcpu_key { __u64 cgroup_id; }; =20 +/* for dumping at the end */ struct { __uint(type, BPF_MAP_TYPE_STACK_TRACE); __uint(key_size, sizeof(__u32)); @@ -41,6 +43,14 @@ struct { __uint(max_entries, MAX_ENTRIES); } stacks SEC(".maps"); =20 +struct offcpu_data { + u64 array[MAX_OFFCPU_LEN]; +}; + +struct stack_data { + u64 array[MAX_STACKS]; +}; + struct { __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY); __uint(key_size, sizeof(__u32)); @@ -48,6 +58,22 @@ struct { __uint(max_entries, MAX_CPUS); } offcpu_output SEC(".maps"); =20 +/* temporary offcpu sample */ +struct { + __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY); + __uint(key_size, sizeof(__u32)); + __uint(value_size, sizeof(struct offcpu_data)); + __uint(max_entries, 1); +} offcpu_payload SEC(".maps"); + +/* cached stack per task storage */ +struct { + __uint(type, BPF_MAP_TYPE_TASK_STORAGE); + __uint(map_flags, BPF_F_NO_PREALLOC); + __type(key, int); + __type(value, struct stack_data); +} stack_cache SEC(".maps"); + struct { __uint(type, BPF_MAP_TYPE_TASK_STORAGE); __uint(map_flags, BPF_F_NO_PREALLOC); @@ -194,12 +220,75 @@ static inline int can_record(struct task_struct *t, i= nt state) return 1; } =20 +static inline bool check_bounds(int index) +{ + if (index < 0 || index >=3D MAX_OFFCPU_LEN) + return false; + + return true; +} + +static inline int copy_stack(struct stack_data *from, + struct offcpu_data *to, int n) +{ + int max_stacks =3D MAX_STACKS, len =3D 0; + + if (!from) + return len; + + for (int i =3D 0; i < max_stacks && from->array[i]; ++i) { + if (check_bounds(n + 2 + i)) { + to->array[n + 2 + i] =3D from->array[i]; + ++len; + } + } + return len; +} + +static int off_cpu_dump(void *ctx, struct offcpu_data *data, struct offcpu= _key *key, + struct stack_data *stack_p, __u64 delta, __u64 timestamp) +{ + int size, n =3D 0, ip_pos =3D -1, len =3D 0; + + if (sample_type & PERF_SAMPLE_TID && check_bounds(n)) + data->array[n++] =3D (u64)key->tgid << 32 | key->pid; + if (sample_type & PERF_SAMPLE_PERIOD && check_bounds(n)) + data->array[n++] =3D delta; + if (sample_type & PERF_SAMPLE_CALLCHAIN && check_bounds(n + 2)) { + /* data->array[n] is callchain->nr (updated later) */ + data->array[n + 1] =3D PERF_CONTEXT_USER; + data->array[n + 2] =3D 0; + + len =3D copy_stack(stack_p, data, n); + + /* update length of callchain */ + data->array[n] =3D len + 1; + + /* update sample ip with the first callchain entry */ + if (ip_pos >=3D 0) + data->array[ip_pos] =3D data->array[n + 2]; + + /* calculate sample callchain data->array length */ + n +=3D len + 2; + } + if (sample_type & PERF_SAMPLE_CGROUP && check_bounds(n)) + data->array[n++] =3D key->cgroup_id; + + size =3D n * sizeof(u64); + if (size >=3D 0 && size <=3D MAX_OFFCPU_LEN * sizeof(u64)) + bpf_perf_event_output(ctx, &offcpu_output, BPF_F_CURRENT_CPU, data, size= ); + + return 0; +} + static int off_cpu_stat(u64 *ctx, struct task_struct *prev, struct task_struct *next, int state) { __u64 ts; __u32 stack_id; struct tstamp_data *pelem; + struct stack_data *stack_p; + int zero =3D 0; =20 ts =3D bpf_ktime_get_ns(); =20 @@ -209,6 +298,21 @@ static int off_cpu_stat(u64 *ctx, struct task_struct *= prev, stack_id =3D bpf_get_stackid(ctx, &stacks, BPF_F_FAST_STACK_CMP | BPF_F_USER_STACK); =20 + /* + * if stacks are successfully collected, cache them to task_storage, they= are then + * dumped if the off-cpu time hits the threshold. + */ + if (stack_id > 0) { + stack_p =3D bpf_task_storage_get(&stack_cache, prev, NULL, + BPF_LOCAL_STORAGE_GET_F_CREATE); + if (stack_p) { + /* to pass the clang result unused warning */ + int __attribute__((unused)) len; + len =3D bpf_get_stack(ctx, stack_p->array, MAX_STACKS * sizeof(u64), + BPF_F_USER_STACK) / sizeof(u64); + } + } + pelem =3D bpf_task_storage_get(&tstamp, prev, NULL, BPF_LOCAL_STORAGE_GET_F_CREATE); if (!pelem) @@ -238,6 +342,14 @@ static int off_cpu_stat(u64 *ctx, struct task_struct *= prev, else bpf_map_update_elem(&off_cpu, &key, &delta, BPF_ANY); =20 + if (delta >=3D offcpu_thresh) { + struct offcpu_data *data =3D bpf_map_lookup_elem(&offcpu_payload, &zero= ); + + stack_p =3D bpf_task_storage_get(&stack_cache, next, NULL, 0); + if (data && stack_p) + off_cpu_dump(ctx, data, &key, stack_p, delta, pelem->timestamp); + } + /* prevent to reuse the timestamp later */ pelem->timestamp =3D 0; } diff --git a/tools/perf/util/off_cpu.h b/tools/perf/util/off_cpu.h index 357231cb1c38..eaf7be92472d 100644 --- a/tools/perf/util/off_cpu.h +++ b/tools/perf/util/off_cpu.h @@ -15,9 +15,15 @@ struct record_opts; #define OFFCPU_SAMPLE_TYPES (PERF_SAMPLE_IDENTIFIER | PERF_SAMPLE_IP | \ PERF_SAMPLE_TID | PERF_SAMPLE_TIME | \ PERF_SAMPLE_ID | PERF_SAMPLE_CPU | \ - PERF_SAMPLE_PERIOD | PERF_SAMPLE_CALLCHAIN | \ + PERF_SAMPLE_PERIOD | PERF_SAMPLE_RAW | \ PERF_SAMPLE_CGROUP) =20 +/* + * for embedded data to overwrite the original sample, duplicated sample t= ypes + * must be set in the original OFFCPU_SAMPLE_TYPES, except for callchain. + */ +#define OFFCPU_EMBEDDED_SAMPLE_TYPES (PERF_SAMPLE_TID | PERF_SAMPLE_PERIO= D | \ + PERF_SAMPLE_CALLCHAIN | PERF_SAMPLE_CGROUP) =20 #ifdef HAVE_BPF_SKEL int off_cpu_prepare(struct evlist *evlist, struct target *target, --=20 2.43.0