| Message ID | 20220518224725.742882-3-namhyung@kernel.org (mailing list archive) |
|---|---|
| State | RFC |
| Delegated to: | BPF |
| Headers | show |
| Series | perf record: Implement off-cpu profiling with BPF (v3) | expand |
| Context | Check | Description |
|---|---|---|
| bpf/vmtest-bpf-next-VM_Test-2 | success | Logs for Kernel LATEST on ubuntu-latest with llvm-15 |
| bpf/vmtest-bpf-next-VM_Test-3 | fail | Logs for Kernel LATEST on z15 with gcc |
| bpf/vmtest-bpf-next-PR | fail | PR summary |
| bpf/vmtest-bpf-next-VM_Test-1 | success | Logs for Kernel LATEST on ubuntu-latest with gcc |
| netdev/tree_selection | success | Not a local patch |
On Wed, May 18, 2022 at 3:47 PM Namhyung Kim <namhyung@kernel.org> wrote: > > Add --off-cpu option to enable the off-cpu profiling with BPF. It'd > use a bpf_output event and rename it to "offcpu-time". Samples will > be synthesized at the end of the record session using data from a BPF > map which contains the aggregated off-cpu time at context switches. > So it needs root privilege to get the off-cpu profiling. > > Each sample will have a separate user stacktrace so it will skip > kernel threads. The sample ip will be set from the stacktrace and > other sample data will be updated accordingly. Currently it only > handles some basic sample types. > > The sample timestamp is set to a dummy value just not to bother with > other events during the sorting. So it has a very big initial value > and increase it on processing each samples. > > Good thing is that it can be used together with regular profiling like > cpu cycles. If you don't want to that, you can use a dummy event to > enable off-cpu profiling only. > > Example output: > $ sudo perf record --off-cpu perf bench sched messaging -l 1000 > > $ sudo perf report --stdio --call-graph=no > # Total Lost Samples: 0 > # > # Samples: 41K of event 'cycles' > # Event count (approx.): 42137343851 > ... > > # Samples: 1K of event 'offcpu-time' > # Event count (approx.): 587990831640 > # > # Children Self Command Shared Object Symbol > # ........ ........ ............... .................. ......................... > # > 81.66% 0.00% sched-messaging libc-2.33.so [.] __libc_start_main > 81.66% 0.00% sched-messaging perf [.] cmd_bench > 81.66% 0.00% sched-messaging perf [.] main > 81.66% 0.00% sched-messaging perf [.] run_builtin > 81.43% 0.00% sched-messaging perf [.] bench_sched_messaging > 40.86% 40.86% sched-messaging libpthread-2.33.so [.] __read > 37.66% 37.66% sched-messaging libpthread-2.33.so [.] __write > 2.91% 2.91% sched-messaging libc-2.33.so [.] __poll > ... > > As you can see it spent most of off-cpu time in read and write in > bench_sched_messaging(). The --call-graph=no was added just to make > the output concise here. > > It uses perf hooks facility to control BPF program during the record > session rather than adding new BPF/off-cpu specific calls. > > Signed-off-by: Namhyung Kim <namhyung@kernel.org> Acked-by: Ian Rogers <irogers@google.com> > --- > tools/perf/Documentation/perf-record.txt | 10 ++ > tools/perf/Makefile.perf | 1 + > tools/perf/builtin-record.c | 25 +++ > tools/perf/util/Build | 1 + > tools/perf/util/bpf_off_cpu.c | 204 +++++++++++++++++++++++ > tools/perf/util/bpf_skel/off_cpu.bpf.c | 139 +++++++++++++++ > tools/perf/util/off_cpu.h | 24 +++ > 7 files changed, 404 insertions(+) > create mode 100644 tools/perf/util/bpf_off_cpu.c > create mode 100644 tools/perf/util/bpf_skel/off_cpu.bpf.c > create mode 100644 tools/perf/util/off_cpu.h > > diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt > index 465be4e62a17..b4e9ef7edfef 100644 > --- a/tools/perf/Documentation/perf-record.txt > +++ b/tools/perf/Documentation/perf-record.txt > @@ -758,6 +758,16 @@ include::intel-hybrid.txt[] > If the URLs is not specified, the value of DEBUGINFOD_URLS > system environment variable is used. > > +--off-cpu:: > + Enable off-cpu profiling with BPF. The BPF program will collect > + task scheduling information with (user) stacktrace and save them > + as sample data of a software event named "offcpu-time". The > + sample period will have the time the task slept in nanoseconds. > + > + Note that BPF can collect stack traces using frame pointer ("fp") > + only, as of now. So the applications built without the frame > + pointer might see bogus addresses. > + > SEE ALSO > -------- > linkperf:perf-stat[1], linkperf:perf-list[1], linkperf:perf-intel-pt[1] > diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf > index 6e5aded855cc..8f738e11356d 100644 > --- a/tools/perf/Makefile.perf > +++ b/tools/perf/Makefile.perf > @@ -1038,6 +1038,7 @@ SKEL_TMP_OUT := $(abspath $(SKEL_OUT)/.tmp) > SKELETONS := $(SKEL_OUT)/bpf_prog_profiler.skel.h > SKELETONS += $(SKEL_OUT)/bperf_leader.skel.h $(SKEL_OUT)/bperf_follower.skel.h > SKELETONS += $(SKEL_OUT)/bperf_cgroup.skel.h $(SKEL_OUT)/func_latency.skel.h > +SKELETONS += $(SKEL_OUT)/off_cpu.skel.h > > $(SKEL_TMP_OUT) $(LIBBPF_OUTPUT): > $(Q)$(MKDIR) -p $@ > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c > index a5cf6a99d67f..91f88501412e 100644 > --- a/tools/perf/builtin-record.c > +++ b/tools/perf/builtin-record.c > @@ -49,6 +49,7 @@ > #include "util/clockid.h" > #include "util/pmu-hybrid.h" > #include "util/evlist-hybrid.h" > +#include "util/off_cpu.h" > #include "asm/bug.h" > #include "perf.h" > #include "cputopo.h" > @@ -162,6 +163,7 @@ struct record { > bool buildid_mmap; > bool timestamp_filename; > bool timestamp_boundary; > + bool off_cpu; > struct switch_output switch_output; > unsigned long long samples; > unsigned long output_max_size; /* = 0: unlimited */ > @@ -903,6 +905,11 @@ static int record__config_text_poke(struct evlist *evlist) > return 0; > } > > +static int record__config_off_cpu(struct record *rec) > +{ > + return off_cpu_prepare(rec->evlist); > +} > + > static bool record__kcore_readable(struct machine *machine) > { > char kcore[PATH_MAX]; > @@ -2600,6 +2607,9 @@ static int __cmd_record(struct record *rec, int argc, const char **argv) > } else > status = err; > > + if (rec->off_cpu) > + rec->bytes_written += off_cpu_write(rec->session); > + > record__synthesize(rec, true); > /* this will be recalculated during process_buildids() */ > rec->samples = 0; > @@ -3324,6 +3334,7 @@ static struct option __record_options[] = { > OPT_CALLBACK_OPTARG(0, "threads", &record.opts, NULL, "spec", > "write collected trace data into several data files using parallel threads", > record__parse_threads), > + OPT_BOOLEAN(0, "off-cpu", &record.off_cpu, "Enable off-cpu analysis"), > OPT_END() > }; > > @@ -3743,6 +3754,12 @@ int cmd_record(int argc, const char **argv) > set_nobuild('\0', "vmlinux", true); > # undef set_nobuild > # undef REASON > +#endif > + > +#ifndef HAVE_BPF_SKEL > +# define set_nobuild(s, l, m, c) set_option_nobuild(record_options, s, l, m, c) > + set_nobuild('\0', "off-cpu", "no BUILD_BPF_SKEL=1", true); > +# undef set_nobuild > #endif > > rec->opts.affinity = PERF_AFFINITY_SYS; > @@ -3981,6 +3998,14 @@ int cmd_record(int argc, const char **argv) > } > } > > + if (rec->off_cpu) { > + err = record__config_off_cpu(rec); > + if (err) { > + pr_err("record__config_off_cpu failed, error %d\n", err); > + goto out; > + } > + } > + > if (record_opts__config(&rec->opts)) { > err = -EINVAL; > goto out; > diff --git a/tools/perf/util/Build b/tools/perf/util/Build > index 9a7209a99e16..a51267d88ca9 100644 > --- a/tools/perf/util/Build > +++ b/tools/perf/util/Build > @@ -147,6 +147,7 @@ perf-$(CONFIG_LIBBPF) += bpf_map.o > perf-$(CONFIG_PERF_BPF_SKEL) += bpf_counter.o > perf-$(CONFIG_PERF_BPF_SKEL) += bpf_counter_cgroup.o > perf-$(CONFIG_PERF_BPF_SKEL) += bpf_ftrace.o > +perf-$(CONFIG_PERF_BPF_SKEL) += bpf_off_cpu.o > perf-$(CONFIG_BPF_PROLOGUE) += bpf-prologue.o > perf-$(CONFIG_LIBELF) += symbol-elf.o > perf-$(CONFIG_LIBELF) += probe-file.o > diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c > new file mode 100644 > index 000000000000..9ed7aca3f4ac > --- /dev/null > +++ b/tools/perf/util/bpf_off_cpu.c > @@ -0,0 +1,204 @@ > +// SPDX-License-Identifier: GPL-2.0 > +#include "util/bpf_counter.h" > +#include "util/debug.h" > +#include "util/evsel.h" > +#include "util/evlist.h" > +#include "util/off_cpu.h" > +#include "util/perf-hooks.h" > +#include "util/session.h" > +#include <bpf/bpf.h> > + > +#include "bpf_skel/off_cpu.skel.h" > + > +#define MAX_STACKS 32 > +/* we don't need actual timestamp, just want to put the samples at last */ > +#define OFF_CPU_TIMESTAMP (~0ull << 32) > + > +static struct off_cpu_bpf *skel; > + > +struct off_cpu_key { > + u32 pid; > + u32 tgid; > + u32 stack_id; > + u32 state; > +}; > + > +union off_cpu_data { > + struct perf_event_header hdr; > + u64 array[1024 / sizeof(u64)]; > +}; > + > +static int off_cpu_config(struct evlist *evlist) > +{ > + struct evsel *evsel; > + struct perf_event_attr attr = { > + .type = PERF_TYPE_SOFTWARE, > + .config = PERF_COUNT_SW_BPF_OUTPUT, > + .size = sizeof(attr), /* to capture ABI version */ > + }; > + char *evname = strdup(OFFCPU_EVENT); > + > + if (evname == NULL) > + return -ENOMEM; > + > + evsel = evsel__new(&attr); > + if (!evsel) { > + free(evname); > + return -ENOMEM; > + } > + > + evsel->core.attr.freq = 1; > + evsel->core.attr.sample_period = 1; > + /* off-cpu analysis depends on stack trace */ > + evsel->core.attr.sample_type = PERF_SAMPLE_CALLCHAIN; > + > + evlist__add(evlist, evsel); > + > + free(evsel->name); > + evsel->name = evname; > + > + return 0; > +} > + > +static void off_cpu_start(void *arg __maybe_unused) > +{ > + skel->bss->enabled = 1; > +} > + > +static void off_cpu_finish(void *arg __maybe_unused) > +{ > + skel->bss->enabled = 0; > + off_cpu_bpf__destroy(skel); > +} > + > +int off_cpu_prepare(struct evlist *evlist) > +{ > + int err; > + > + if (off_cpu_config(evlist) < 0) { > + pr_err("Failed to config off-cpu BPF event\n"); > + return -1; > + } > + > + set_max_rlimit(); > + > + skel = off_cpu_bpf__open_and_load(); > + if (!skel) { > + pr_err("Failed to open off-cpu BPF skeleton\n"); > + return -1; > + } > + > + err = off_cpu_bpf__attach(skel); > + if (err) { > + pr_err("Failed to attach off-cpu BPF skeleton\n"); > + goto out; > + } > + > + if (perf_hooks__set_hook("record_start", off_cpu_start, NULL) || > + perf_hooks__set_hook("record_end", off_cpu_finish, NULL)) { An off-topic thought here. I was looking at tool events and thinking that rather than have global state and the counter reading getting those global values, it would be nice if the tool events had private state that was created on open, freed on close and then did the appropriate thing for enable/read/disable. If we were object oriented I was thinking tool events could be a subclass of evsel that would override the appropriate functions. Something that strikes me as silly is that tool events have a dummy event file descriptor from perf_event_open, in part because the evsel code paths are shared. Anyway, if we made evsels have something like a virtual method table, we could do similar tricks with off-cpu and BPF created events. Possibly this could lead to better structured code and more reuse. Thanks, Ian > + pr_err("Failed to attach off-cpu skeleton\n"); > + goto out; > + } > + > + return 0; > + > +out: > + off_cpu_bpf__destroy(skel); > + return -1; > +} > + > +int off_cpu_write(struct perf_session *session) > +{ > + int bytes = 0, size; > + int fd, stack; > + u64 sample_type, val, sid = 0; > + struct evsel *evsel; > + struct perf_data_file *file = &session->data->file; > + struct off_cpu_key prev, key; > + union off_cpu_data data = { > + .hdr = { > + .type = PERF_RECORD_SAMPLE, > + .misc = PERF_RECORD_MISC_USER, > + }, > + }; > + u64 tstamp = OFF_CPU_TIMESTAMP; > + > + skel->bss->enabled = 0; > + > + evsel = evlist__find_evsel_by_str(session->evlist, OFFCPU_EVENT); > + if (evsel == NULL) { > + pr_err("%s evsel not found\n", OFFCPU_EVENT); > + return 0; > + } > + > + sample_type = evsel->core.attr.sample_type; > + > + if (sample_type & (PERF_SAMPLE_ID | PERF_SAMPLE_IDENTIFIER)) { > + if (evsel->core.id) > + sid = evsel->core.id[0]; > + } > + > + fd = bpf_map__fd(skel->maps.off_cpu); > + stack = bpf_map__fd(skel->maps.stacks); > + memset(&prev, 0, sizeof(prev)); > + > + while (!bpf_map_get_next_key(fd, &prev, &key)) { > + int n = 1; /* start from perf_event_header */ > + int ip_pos = -1; > + > + bpf_map_lookup_elem(fd, &key, &val); > + > + if (sample_type & PERF_SAMPLE_IDENTIFIER) > + data.array[n++] = sid; > + if (sample_type & PERF_SAMPLE_IP) { > + ip_pos = n; > + data.array[n++] = 0; /* will be updated */ > + } > + if (sample_type & PERF_SAMPLE_TID) > + data.array[n++] = (u64)key.pid << 32 | key.tgid; > + if (sample_type & PERF_SAMPLE_TIME) > + data.array[n++] = tstamp; > + if (sample_type & PERF_SAMPLE_ID) > + data.array[n++] = sid; > + if (sample_type & PERF_SAMPLE_CPU) > + data.array[n++] = 0; > + if (sample_type & PERF_SAMPLE_PERIOD) > + data.array[n++] = val; > + if (sample_type & PERF_SAMPLE_CALLCHAIN) { > + int len = 0; > + > + /* data.array[n] is callchain->nr (updated later) */ > + data.array[n + 1] = PERF_CONTEXT_USER; > + data.array[n + 2] = 0; > + > + bpf_map_lookup_elem(stack, &key.stack_id, &data.array[n + 2]); > + while (data.array[n + 2 + len]) > + len++; > + > + /* update length of callchain */ > + data.array[n] = len + 1; > + > + /* update sample ip with the first callchain entry */ > + if (ip_pos >= 0) > + data.array[ip_pos] = data.array[n + 2]; > + > + /* calculate sample callchain data array length */ > + n += len + 2; > + } > + /* TODO: handle more sample types */ > + > + size = n * sizeof(u64); > + data.hdr.size = size; > + bytes += size; > + > + if (perf_data_file__write(file, &data, size) < 0) { > + pr_err("failed to write perf data, error: %m\n"); > + return bytes; > + } > + > + prev = key; > + /* increase dummy timestamp to sort later samples */ > + tstamp++; > + } > + return bytes; > +} > diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c > new file mode 100644 > index 000000000000..5173ed882fdf > --- /dev/null > +++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c > @@ -0,0 +1,139 @@ > +// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) > +// Copyright (c) 2022 Google > +#include "vmlinux.h" > +#include <bpf/bpf_helpers.h> > +#include <bpf/bpf_tracing.h> > +#include <bpf/bpf_core_read.h> > + > +/* task->flags for off-cpu analysis */ > +#define PF_KTHREAD 0x00200000 /* I am a kernel thread */ > + > +/* task->state for off-cpu analysis */ > +#define TASK_INTERRUPTIBLE 0x0001 > +#define TASK_UNINTERRUPTIBLE 0x0002 > + > +#define MAX_STACKS 32 > +#define MAX_ENTRIES 102400 > + > +struct tstamp_data { > + __u32 stack_id; > + __u32 state; > + __u64 timestamp; > +}; > + > +struct offcpu_key { > + __u32 pid; > + __u32 tgid; > + __u32 stack_id; > + __u32 state; > +}; > + > +struct { > + __uint(type, BPF_MAP_TYPE_STACK_TRACE); > + __uint(key_size, sizeof(__u32)); > + __uint(value_size, MAX_STACKS * sizeof(__u64)); > + __uint(max_entries, MAX_ENTRIES); > +} stacks SEC(".maps"); > + > +struct { > + __uint(type, BPF_MAP_TYPE_TASK_STORAGE); > + __uint(map_flags, BPF_F_NO_PREALLOC); > + __type(key, int); > + __type(value, struct tstamp_data); > +} tstamp SEC(".maps"); > + > +struct { > + __uint(type, BPF_MAP_TYPE_HASH); > + __uint(key_size, sizeof(struct offcpu_key)); > + __uint(value_size, sizeof(__u64)); > + __uint(max_entries, MAX_ENTRIES); > +} off_cpu SEC(".maps"); > + > +/* old kernel task_struct definition */ > +struct task_struct___old { > + long state; > +} __attribute__((preserve_access_index)); > + > +int enabled = 0; > + > +/* > + * Old kernel used to call it task_struct->state and now it's '__state'. > + * Use BPF CO-RE "ignored suffix rule" to deal with it like below: > + * > + * https://nakryiko.com/posts/bpf-core-reference-guide/#handling-incompatible-field-and-type-changes > + */ > +static inline int get_task_state(struct task_struct *t) > +{ > + if (bpf_core_field_exists(t->__state)) > + return BPF_CORE_READ(t, __state); > + > + /* recast pointer to capture task_struct___old type for compiler */ > + struct task_struct___old *t_old = (void *)t; > + > + /* now use old "state" name of the field */ > + return BPF_CORE_READ(t_old, state); > +} > + > +SEC("tp_btf/sched_switch") > +int on_switch(u64 *ctx) > +{ > + __u64 ts; > + int state; > + __u32 stack_id; > + struct task_struct *prev, *next; > + struct tstamp_data *pelem; > + > + if (!enabled) > + return 0; > + > + prev = (struct task_struct *)ctx[1]; > + next = (struct task_struct *)ctx[2]; > + state = get_task_state(prev); > + > + ts = bpf_ktime_get_ns(); > + > + if (prev->flags & PF_KTHREAD) > + goto next; > + if (state != TASK_INTERRUPTIBLE && > + state != TASK_UNINTERRUPTIBLE) > + goto next; > + > + stack_id = bpf_get_stackid(ctx, &stacks, > + BPF_F_FAST_STACK_CMP | BPF_F_USER_STACK); > + > + pelem = bpf_task_storage_get(&tstamp, prev, NULL, > + BPF_LOCAL_STORAGE_GET_F_CREATE); > + if (!pelem) > + goto next; > + > + pelem->timestamp = ts; > + pelem->state = state; > + pelem->stack_id = stack_id; > + > +next: > + pelem = bpf_task_storage_get(&tstamp, next, NULL, 0); > + > + if (pelem && pelem->timestamp) { > + struct offcpu_key key = { > + .pid = next->pid, > + .tgid = next->tgid, > + .stack_id = pelem->stack_id, > + .state = pelem->state, > + }; > + __u64 delta = ts - pelem->timestamp; > + __u64 *total; > + > + total = bpf_map_lookup_elem(&off_cpu, &key); > + if (total) > + *total += delta; > + else > + bpf_map_update_elem(&off_cpu, &key, &delta, BPF_ANY); > + > + /* prevent to reuse the timestamp later */ > + pelem->timestamp = 0; > + } > + > + return 0; > +} > + > +char LICENSE[] SEC("license") = "Dual BSD/GPL"; > diff --git a/tools/perf/util/off_cpu.h b/tools/perf/util/off_cpu.h > new file mode 100644 > index 000000000000..375d03c424ea > --- /dev/null > +++ b/tools/perf/util/off_cpu.h > @@ -0,0 +1,24 @@ > +#ifndef PERF_UTIL_OFF_CPU_H > +#define PERF_UTIL_OFF_CPU_H > + > +struct evlist; > +struct perf_session; > + > +#define OFFCPU_EVENT "offcpu-time" > + > +#ifdef HAVE_BPF_SKEL > +int off_cpu_prepare(struct evlist *evlist); > +int off_cpu_write(struct perf_session *session); > +#else > +static inline int off_cpu_prepare(struct evlist *evlist __maybe_unused) > +{ > + return -1; > +} > + > +static inline int off_cpu_write(struct perf_session *session __maybe_unused) > +{ > + return -1; > +} > +#endif > + > +#endif /* PERF_UTIL_OFF_CPU_H */ > -- > 2.36.1.124.g0e6072fb45-goog >
Hi Ian, On Wed, May 18, 2022 at 8:58 PM Ian Rogers <irogers@google.com> wrote: > > On Wed, May 18, 2022 at 3:47 PM Namhyung Kim <namhyung@kernel.org> wrote: > > > > Add --off-cpu option to enable the off-cpu profiling with BPF. It'd > > use a bpf_output event and rename it to "offcpu-time". Samples will > > be synthesized at the end of the record session using data from a BPF > > map which contains the aggregated off-cpu time at context switches. > > So it needs root privilege to get the off-cpu profiling. > > > > Each sample will have a separate user stacktrace so it will skip > > kernel threads. The sample ip will be set from the stacktrace and > > other sample data will be updated accordingly. Currently it only > > handles some basic sample types. > > > > The sample timestamp is set to a dummy value just not to bother with > > other events during the sorting. So it has a very big initial value > > and increase it on processing each samples. > > > > Good thing is that it can be used together with regular profiling like > > cpu cycles. If you don't want to that, you can use a dummy event to > > enable off-cpu profiling only. > > > > Example output: > > $ sudo perf record --off-cpu perf bench sched messaging -l 1000 > > > > $ sudo perf report --stdio --call-graph=no > > # Total Lost Samples: 0 > > # > > # Samples: 41K of event 'cycles' > > # Event count (approx.): 42137343851 > > ... > > > > # Samples: 1K of event 'offcpu-time' > > # Event count (approx.): 587990831640 > > # > > # Children Self Command Shared Object Symbol > > # ........ ........ ............... .................. ......................... > > # > > 81.66% 0.00% sched-messaging libc-2.33.so [.] __libc_start_main > > 81.66% 0.00% sched-messaging perf [.] cmd_bench > > 81.66% 0.00% sched-messaging perf [.] main > > 81.66% 0.00% sched-messaging perf [.] run_builtin > > 81.43% 0.00% sched-messaging perf [.] bench_sched_messaging > > 40.86% 40.86% sched-messaging libpthread-2.33.so [.] __read > > 37.66% 37.66% sched-messaging libpthread-2.33.so [.] __write > > 2.91% 2.91% sched-messaging libc-2.33.so [.] __poll > > ... > > > > As you can see it spent most of off-cpu time in read and write in > > bench_sched_messaging(). The --call-graph=no was added just to make > > the output concise here. > > > > It uses perf hooks facility to control BPF program during the record > > session rather than adding new BPF/off-cpu specific calls. > > > > Signed-off-by: Namhyung Kim <namhyung@kernel.org> > > Acked-by: Ian Rogers <irogers@google.com> > > > --- > > tools/perf/Documentation/perf-record.txt | 10 ++ > > tools/perf/Makefile.perf | 1 + > > tools/perf/builtin-record.c | 25 +++ > > tools/perf/util/Build | 1 + > > tools/perf/util/bpf_off_cpu.c | 204 +++++++++++++++++++++++ > > tools/perf/util/bpf_skel/off_cpu.bpf.c | 139 +++++++++++++++ > > tools/perf/util/off_cpu.h | 24 +++ > > 7 files changed, 404 insertions(+) > > create mode 100644 tools/perf/util/bpf_off_cpu.c > > create mode 100644 tools/perf/util/bpf_skel/off_cpu.bpf.c > > create mode 100644 tools/perf/util/off_cpu.h > > > > diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt > > index 465be4e62a17..b4e9ef7edfef 100644 > > --- a/tools/perf/Documentation/perf-record.txt > > +++ b/tools/perf/Documentation/perf-record.txt > > @@ -758,6 +758,16 @@ include::intel-hybrid.txt[] > > If the URLs is not specified, the value of DEBUGINFOD_URLS > > system environment variable is used. > > > > +--off-cpu:: > > + Enable off-cpu profiling with BPF. The BPF program will collect > > + task scheduling information with (user) stacktrace and save them > > + as sample data of a software event named "offcpu-time". The > > + sample period will have the time the task slept in nanoseconds. > > + > > + Note that BPF can collect stack traces using frame pointer ("fp") > > + only, as of now. So the applications built without the frame > > + pointer might see bogus addresses. > > + > > SEE ALSO > > -------- > > linkperf:perf-stat[1], linkperf:perf-list[1], linkperf:perf-intel-pt[1] > > diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf > > index 6e5aded855cc..8f738e11356d 100644 > > --- a/tools/perf/Makefile.perf > > +++ b/tools/perf/Makefile.perf > > @@ -1038,6 +1038,7 @@ SKEL_TMP_OUT := $(abspath $(SKEL_OUT)/.tmp) > > SKELETONS := $(SKEL_OUT)/bpf_prog_profiler.skel.h > > SKELETONS += $(SKEL_OUT)/bperf_leader.skel.h $(SKEL_OUT)/bperf_follower.skel.h > > SKELETONS += $(SKEL_OUT)/bperf_cgroup.skel.h $(SKEL_OUT)/func_latency.skel.h > > +SKELETONS += $(SKEL_OUT)/off_cpu.skel.h > > > > $(SKEL_TMP_OUT) $(LIBBPF_OUTPUT): > > $(Q)$(MKDIR) -p $@ > > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c > > index a5cf6a99d67f..91f88501412e 100644 > > --- a/tools/perf/builtin-record.c > > +++ b/tools/perf/builtin-record.c > > @@ -49,6 +49,7 @@ > > #include "util/clockid.h" > > #include "util/pmu-hybrid.h" > > #include "util/evlist-hybrid.h" > > +#include "util/off_cpu.h" > > #include "asm/bug.h" > > #include "perf.h" > > #include "cputopo.h" > > @@ -162,6 +163,7 @@ struct record { > > bool buildid_mmap; > > bool timestamp_filename; > > bool timestamp_boundary; > > + bool off_cpu; > > struct switch_output switch_output; > > unsigned long long samples; > > unsigned long output_max_size; /* = 0: unlimited */ > > @@ -903,6 +905,11 @@ static int record__config_text_poke(struct evlist *evlist) > > return 0; > > } > > > > +static int record__config_off_cpu(struct record *rec) > > +{ > > + return off_cpu_prepare(rec->evlist); > > +} > > + > > static bool record__kcore_readable(struct machine *machine) > > { > > char kcore[PATH_MAX]; > > @@ -2600,6 +2607,9 @@ static int __cmd_record(struct record *rec, int argc, const char **argv) > > } else > > status = err; > > > > + if (rec->off_cpu) > > + rec->bytes_written += off_cpu_write(rec->session); > > + > > record__synthesize(rec, true); > > /* this will be recalculated during process_buildids() */ > > rec->samples = 0; > > @@ -3324,6 +3334,7 @@ static struct option __record_options[] = { > > OPT_CALLBACK_OPTARG(0, "threads", &record.opts, NULL, "spec", > > "write collected trace data into several data files using parallel threads", > > record__parse_threads), > > + OPT_BOOLEAN(0, "off-cpu", &record.off_cpu, "Enable off-cpu analysis"), > > OPT_END() > > }; > > > > @@ -3743,6 +3754,12 @@ int cmd_record(int argc, const char **argv) > > set_nobuild('\0', "vmlinux", true); > > # undef set_nobuild > > # undef REASON > > +#endif > > + > > +#ifndef HAVE_BPF_SKEL > > +# define set_nobuild(s, l, m, c) set_option_nobuild(record_options, s, l, m, c) > > + set_nobuild('\0', "off-cpu", "no BUILD_BPF_SKEL=1", true); > > +# undef set_nobuild > > #endif > > > > rec->opts.affinity = PERF_AFFINITY_SYS; > > @@ -3981,6 +3998,14 @@ int cmd_record(int argc, const char **argv) > > } > > } > > > > + if (rec->off_cpu) { > > + err = record__config_off_cpu(rec); > > + if (err) { > > + pr_err("record__config_off_cpu failed, error %d\n", err); > > + goto out; > > + } > > + } > > + > > if (record_opts__config(&rec->opts)) { > > err = -EINVAL; > > goto out; > > diff --git a/tools/perf/util/Build b/tools/perf/util/Build > > index 9a7209a99e16..a51267d88ca9 100644 > > --- a/tools/perf/util/Build > > +++ b/tools/perf/util/Build > > @@ -147,6 +147,7 @@ perf-$(CONFIG_LIBBPF) += bpf_map.o > > perf-$(CONFIG_PERF_BPF_SKEL) += bpf_counter.o > > perf-$(CONFIG_PERF_BPF_SKEL) += bpf_counter_cgroup.o > > perf-$(CONFIG_PERF_BPF_SKEL) += bpf_ftrace.o > > +perf-$(CONFIG_PERF_BPF_SKEL) += bpf_off_cpu.o > > perf-$(CONFIG_BPF_PROLOGUE) += bpf-prologue.o > > perf-$(CONFIG_LIBELF) += symbol-elf.o > > perf-$(CONFIG_LIBELF) += probe-file.o > > diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c > > new file mode 100644 > > index 000000000000..9ed7aca3f4ac > > --- /dev/null > > +++ b/tools/perf/util/bpf_off_cpu.c > > @@ -0,0 +1,204 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > +#include "util/bpf_counter.h" > > +#include "util/debug.h" > > +#include "util/evsel.h" > > +#include "util/evlist.h" > > +#include "util/off_cpu.h" > > +#include "util/perf-hooks.h" > > +#include "util/session.h" > > +#include <bpf/bpf.h> > > + > > +#include "bpf_skel/off_cpu.skel.h" > > + > > +#define MAX_STACKS 32 > > +/* we don't need actual timestamp, just want to put the samples at last */ > > +#define OFF_CPU_TIMESTAMP (~0ull << 32) > > + > > +static struct off_cpu_bpf *skel; > > + > > +struct off_cpu_key { > > + u32 pid; > > + u32 tgid; > > + u32 stack_id; > > + u32 state; > > +}; > > + > > +union off_cpu_data { > > + struct perf_event_header hdr; > > + u64 array[1024 / sizeof(u64)]; > > +}; > > + > > +static int off_cpu_config(struct evlist *evlist) > > +{ > > + struct evsel *evsel; > > + struct perf_event_attr attr = { > > + .type = PERF_TYPE_SOFTWARE, > > + .config = PERF_COUNT_SW_BPF_OUTPUT, > > + .size = sizeof(attr), /* to capture ABI version */ > > + }; > > + char *evname = strdup(OFFCPU_EVENT); > > + > > + if (evname == NULL) > > + return -ENOMEM; > > + > > + evsel = evsel__new(&attr); > > + if (!evsel) { > > + free(evname); > > + return -ENOMEM; > > + } > > + > > + evsel->core.attr.freq = 1; > > + evsel->core.attr.sample_period = 1; > > + /* off-cpu analysis depends on stack trace */ > > + evsel->core.attr.sample_type = PERF_SAMPLE_CALLCHAIN; > > + > > + evlist__add(evlist, evsel); > > + > > + free(evsel->name); > > + evsel->name = evname; > > + > > + return 0; > > +} > > + > > +static void off_cpu_start(void *arg __maybe_unused) > > +{ > > + skel->bss->enabled = 1; > > +} > > + > > +static void off_cpu_finish(void *arg __maybe_unused) > > +{ > > + skel->bss->enabled = 0; > > + off_cpu_bpf__destroy(skel); > > +} > > + > > +int off_cpu_prepare(struct evlist *evlist) > > +{ > > + int err; > > + > > + if (off_cpu_config(evlist) < 0) { > > + pr_err("Failed to config off-cpu BPF event\n"); > > + return -1; > > + } > > + > > + set_max_rlimit(); > > + > > + skel = off_cpu_bpf__open_and_load(); > > + if (!skel) { > > + pr_err("Failed to open off-cpu BPF skeleton\n"); > > + return -1; > > + } > > + > > + err = off_cpu_bpf__attach(skel); > > + if (err) { > > + pr_err("Failed to attach off-cpu BPF skeleton\n"); > > + goto out; > > + } > > + > > + if (perf_hooks__set_hook("record_start", off_cpu_start, NULL) || > > + perf_hooks__set_hook("record_end", off_cpu_finish, NULL)) { > > An off-topic thought here. I was looking at tool events and thinking > that rather than have global state and the counter reading getting > those global values, it would be nice if the tool events had private > state that was created on open, freed on close and then did the > appropriate thing for enable/read/disable. If we were object oriented > I was thinking tool events could be a subclass of evsel that would > override the appropriate functions. Something that strikes me as silly > is that tool events have a dummy event file descriptor from > perf_event_open, in part because the evsel code paths are shared. > Anyway, if we made evsels have something like a virtual method table, > we could do similar tricks with off-cpu and BPF created events. > Possibly this could lead to better structured code and more reuse. Thanks for your review. Yeah I think it makes sense to change the offcpu-time event as a tool event and to skip actual open/read/close operations. It would be a good follow up work. Using a dummy event still has a syscall overhead and tool events don't need the syscalls. Maybe we can add some logic in the evlist code to skip the tool events. Thanks, Namhyung
On Wed, May 18, 2022 at 3:47 PM Namhyung Kim <namhyung@kernel.org> wrote: > > Add --off-cpu option to enable the off-cpu profiling with BPF. It'd > use a bpf_output event and rename it to "offcpu-time". Samples will > be synthesized at the end of the record session using data from a BPF > map which contains the aggregated off-cpu time at context switches. > So it needs root privilege to get the off-cpu profiling. > > Each sample will have a separate user stacktrace so it will skip > kernel threads. The sample ip will be set from the stacktrace and > other sample data will be updated accordingly. Currently it only > handles some basic sample types. > > The sample timestamp is set to a dummy value just not to bother with > other events during the sorting. So it has a very big initial value > and increase it on processing each samples. > > Good thing is that it can be used together with regular profiling like > cpu cycles. If you don't want to that, you can use a dummy event to > enable off-cpu profiling only. > > Example output: > $ sudo perf record --off-cpu perf bench sched messaging -l 1000 > > $ sudo perf report --stdio --call-graph=no > # Total Lost Samples: 0 > # > # Samples: 41K of event 'cycles' > # Event count (approx.): 42137343851 > ... > > # Samples: 1K of event 'offcpu-time' > # Event count (approx.): 587990831640 > # > # Children Self Command Shared Object Symbol > # ........ ........ ............... .................. ......................... > # > 81.66% 0.00% sched-messaging libc-2.33.so [.] __libc_start_main > 81.66% 0.00% sched-messaging perf [.] cmd_bench > 81.66% 0.00% sched-messaging perf [.] main > 81.66% 0.00% sched-messaging perf [.] run_builtin > 81.43% 0.00% sched-messaging perf [.] bench_sched_messaging > 40.86% 40.86% sched-messaging libpthread-2.33.so [.] __read > 37.66% 37.66% sched-messaging libpthread-2.33.so [.] __write > 2.91% 2.91% sched-messaging libc-2.33.so [.] __poll > ... > > As you can see it spent most of off-cpu time in read and write in > bench_sched_messaging(). The --call-graph=no was added just to make > the output concise here. > > It uses perf hooks facility to control BPF program during the record > session rather than adding new BPF/off-cpu specific calls. > > Signed-off-by: Namhyung Kim <namhyung@kernel.org> > --- > tools/perf/Documentation/perf-record.txt | 10 ++ > tools/perf/Makefile.perf | 1 + > tools/perf/builtin-record.c | 25 +++ > tools/perf/util/Build | 1 + > tools/perf/util/bpf_off_cpu.c | 204 +++++++++++++++++++++++ > tools/perf/util/bpf_skel/off_cpu.bpf.c | 139 +++++++++++++++ > tools/perf/util/off_cpu.h | 24 +++ > 7 files changed, 404 insertions(+) > create mode 100644 tools/perf/util/bpf_off_cpu.c > create mode 100644 tools/perf/util/bpf_skel/off_cpu.bpf.c > create mode 100644 tools/perf/util/off_cpu.h > > diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt > index 465be4e62a17..b4e9ef7edfef 100644 > --- a/tools/perf/Documentation/perf-record.txt > +++ b/tools/perf/Documentation/perf-record.txt > @@ -758,6 +758,16 @@ include::intel-hybrid.txt[] > If the URLs is not specified, the value of DEBUGINFOD_URLS > system environment variable is used. > > +--off-cpu:: > + Enable off-cpu profiling with BPF. The BPF program will collect > + task scheduling information with (user) stacktrace and save them > + as sample data of a software event named "offcpu-time". The > + sample period will have the time the task slept in nanoseconds. > + > + Note that BPF can collect stack traces using frame pointer ("fp") > + only, as of now. So the applications built without the frame > + pointer might see bogus addresses. > + > SEE ALSO > -------- > linkperf:perf-stat[1], linkperf:perf-list[1], linkperf:perf-intel-pt[1] > diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf > index 6e5aded855cc..8f738e11356d 100644 > --- a/tools/perf/Makefile.perf > +++ b/tools/perf/Makefile.perf > @@ -1038,6 +1038,7 @@ SKEL_TMP_OUT := $(abspath $(SKEL_OUT)/.tmp) > SKELETONS := $(SKEL_OUT)/bpf_prog_profiler.skel.h > SKELETONS += $(SKEL_OUT)/bperf_leader.skel.h $(SKEL_OUT)/bperf_follower.skel.h > SKELETONS += $(SKEL_OUT)/bperf_cgroup.skel.h $(SKEL_OUT)/func_latency.skel.h > +SKELETONS += $(SKEL_OUT)/off_cpu.skel.h > > $(SKEL_TMP_OUT) $(LIBBPF_OUTPUT): > $(Q)$(MKDIR) -p $@ > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c > index a5cf6a99d67f..91f88501412e 100644 > --- a/tools/perf/builtin-record.c > +++ b/tools/perf/builtin-record.c > @@ -49,6 +49,7 @@ > #include "util/clockid.h" > #include "util/pmu-hybrid.h" > #include "util/evlist-hybrid.h" > +#include "util/off_cpu.h" > #include "asm/bug.h" > #include "perf.h" > #include "cputopo.h" > @@ -162,6 +163,7 @@ struct record { > bool buildid_mmap; > bool timestamp_filename; > bool timestamp_boundary; > + bool off_cpu; > struct switch_output switch_output; > unsigned long long samples; > unsigned long output_max_size; /* = 0: unlimited */ > @@ -903,6 +905,11 @@ static int record__config_text_poke(struct evlist *evlist) > return 0; > } > > +static int record__config_off_cpu(struct record *rec) > +{ > + return off_cpu_prepare(rec->evlist); > +} > + > static bool record__kcore_readable(struct machine *machine) > { > char kcore[PATH_MAX]; > @@ -2600,6 +2607,9 @@ static int __cmd_record(struct record *rec, int argc, const char **argv) > } else > status = err; > > + if (rec->off_cpu) > + rec->bytes_written += off_cpu_write(rec->session); > + > record__synthesize(rec, true); > /* this will be recalculated during process_buildids() */ > rec->samples = 0; > @@ -3324,6 +3334,7 @@ static struct option __record_options[] = { > OPT_CALLBACK_OPTARG(0, "threads", &record.opts, NULL, "spec", > "write collected trace data into several data files using parallel threads", > record__parse_threads), > + OPT_BOOLEAN(0, "off-cpu", &record.off_cpu, "Enable off-cpu analysis"), > OPT_END() > }; > > @@ -3743,6 +3754,12 @@ int cmd_record(int argc, const char **argv) > set_nobuild('\0', "vmlinux", true); > # undef set_nobuild > # undef REASON > +#endif > + > +#ifndef HAVE_BPF_SKEL > +# define set_nobuild(s, l, m, c) set_option_nobuild(record_options, s, l, m, c) > + set_nobuild('\0', "off-cpu", "no BUILD_BPF_SKEL=1", true); > +# undef set_nobuild > #endif > > rec->opts.affinity = PERF_AFFINITY_SYS; > @@ -3981,6 +3998,14 @@ int cmd_record(int argc, const char **argv) > } > } > > + if (rec->off_cpu) { > + err = record__config_off_cpu(rec); > + if (err) { > + pr_err("record__config_off_cpu failed, error %d\n", err); > + goto out; > + } > + } > + > if (record_opts__config(&rec->opts)) { > err = -EINVAL; > goto out; > diff --git a/tools/perf/util/Build b/tools/perf/util/Build > index 9a7209a99e16..a51267d88ca9 100644 > --- a/tools/perf/util/Build > +++ b/tools/perf/util/Build > @@ -147,6 +147,7 @@ perf-$(CONFIG_LIBBPF) += bpf_map.o > perf-$(CONFIG_PERF_BPF_SKEL) += bpf_counter.o > perf-$(CONFIG_PERF_BPF_SKEL) += bpf_counter_cgroup.o > perf-$(CONFIG_PERF_BPF_SKEL) += bpf_ftrace.o > +perf-$(CONFIG_PERF_BPF_SKEL) += bpf_off_cpu.o > perf-$(CONFIG_BPF_PROLOGUE) += bpf-prologue.o > perf-$(CONFIG_LIBELF) += symbol-elf.o > perf-$(CONFIG_LIBELF) += probe-file.o > diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c > new file mode 100644 > index 000000000000..9ed7aca3f4ac > --- /dev/null > +++ b/tools/perf/util/bpf_off_cpu.c > @@ -0,0 +1,204 @@ > +// SPDX-License-Identifier: GPL-2.0 > +#include "util/bpf_counter.h" > +#include "util/debug.h" > +#include "util/evsel.h" > +#include "util/evlist.h" > +#include "util/off_cpu.h" > +#include "util/perf-hooks.h" > +#include "util/session.h" > +#include <bpf/bpf.h> > + > +#include "bpf_skel/off_cpu.skel.h" > + > +#define MAX_STACKS 32 > +/* we don't need actual timestamp, just want to put the samples at last */ > +#define OFF_CPU_TIMESTAMP (~0ull << 32) > + > +static struct off_cpu_bpf *skel; > + > +struct off_cpu_key { > + u32 pid; > + u32 tgid; > + u32 stack_id; > + u32 state; > +}; > + > +union off_cpu_data { > + struct perf_event_header hdr; > + u64 array[1024 / sizeof(u64)]; > +}; > + > +static int off_cpu_config(struct evlist *evlist) > +{ > + struct evsel *evsel; > + struct perf_event_attr attr = { > + .type = PERF_TYPE_SOFTWARE, > + .config = PERF_COUNT_SW_BPF_OUTPUT, > + .size = sizeof(attr), /* to capture ABI version */ > + }; > + char *evname = strdup(OFFCPU_EVENT); > + > + if (evname == NULL) > + return -ENOMEM; > + > + evsel = evsel__new(&attr); > + if (!evsel) { > + free(evname); > + return -ENOMEM; > + } > + > + evsel->core.attr.freq = 1; > + evsel->core.attr.sample_period = 1; > + /* off-cpu analysis depends on stack trace */ > + evsel->core.attr.sample_type = PERF_SAMPLE_CALLCHAIN; > + > + evlist__add(evlist, evsel); > + > + free(evsel->name); > + evsel->name = evname; > + > + return 0; > +} > + > +static void off_cpu_start(void *arg __maybe_unused) > +{ > + skel->bss->enabled = 1; > +} > + > +static void off_cpu_finish(void *arg __maybe_unused) > +{ > + skel->bss->enabled = 0; > + off_cpu_bpf__destroy(skel); > +} > + > +int off_cpu_prepare(struct evlist *evlist) > +{ > + int err; > + > + if (off_cpu_config(evlist) < 0) { > + pr_err("Failed to config off-cpu BPF event\n"); > + return -1; > + } > + > + set_max_rlimit(); > + > + skel = off_cpu_bpf__open_and_load(); > + if (!skel) { > + pr_err("Failed to open off-cpu BPF skeleton\n"); > + return -1; > + } > + > + err = off_cpu_bpf__attach(skel); > + if (err) { > + pr_err("Failed to attach off-cpu BPF skeleton\n"); > + goto out; > + } > + > + if (perf_hooks__set_hook("record_start", off_cpu_start, NULL) || > + perf_hooks__set_hook("record_end", off_cpu_finish, NULL)) { > + pr_err("Failed to attach off-cpu skeleton\n"); > + goto out; > + } > + > + return 0; > + > +out: > + off_cpu_bpf__destroy(skel); > + return -1; > +} > + > +int off_cpu_write(struct perf_session *session) > +{ > + int bytes = 0, size; > + int fd, stack; > + u64 sample_type, val, sid = 0; > + struct evsel *evsel; > + struct perf_data_file *file = &session->data->file; > + struct off_cpu_key prev, key; > + union off_cpu_data data = { > + .hdr = { > + .type = PERF_RECORD_SAMPLE, > + .misc = PERF_RECORD_MISC_USER, > + }, > + }; > + u64 tstamp = OFF_CPU_TIMESTAMP; > + > + skel->bss->enabled = 0; > + > + evsel = evlist__find_evsel_by_str(session->evlist, OFFCPU_EVENT); > + if (evsel == NULL) { > + pr_err("%s evsel not found\n", OFFCPU_EVENT); > + return 0; > + } > + > + sample_type = evsel->core.attr.sample_type; > + > + if (sample_type & (PERF_SAMPLE_ID | PERF_SAMPLE_IDENTIFIER)) { > + if (evsel->core.id) > + sid = evsel->core.id[0]; > + } > + > + fd = bpf_map__fd(skel->maps.off_cpu); > + stack = bpf_map__fd(skel->maps.stacks); > + memset(&prev, 0, sizeof(prev)); > + > + while (!bpf_map_get_next_key(fd, &prev, &key)) { > + int n = 1; /* start from perf_event_header */ > + int ip_pos = -1; > + > + bpf_map_lookup_elem(fd, &key, &val); > + > + if (sample_type & PERF_SAMPLE_IDENTIFIER) > + data.array[n++] = sid; > + if (sample_type & PERF_SAMPLE_IP) { > + ip_pos = n; > + data.array[n++] = 0; /* will be updated */ > + } > + if (sample_type & PERF_SAMPLE_TID) > + data.array[n++] = (u64)key.pid << 32 | key.tgid; > + if (sample_type & PERF_SAMPLE_TIME) > + data.array[n++] = tstamp; > + if (sample_type & PERF_SAMPLE_ID) > + data.array[n++] = sid; > + if (sample_type & PERF_SAMPLE_CPU) > + data.array[n++] = 0; > + if (sample_type & PERF_SAMPLE_PERIOD) > + data.array[n++] = val; > + if (sample_type & PERF_SAMPLE_CALLCHAIN) { > + int len = 0; > + > + /* data.array[n] is callchain->nr (updated later) */ > + data.array[n + 1] = PERF_CONTEXT_USER; > + data.array[n + 2] = 0; > + > + bpf_map_lookup_elem(stack, &key.stack_id, &data.array[n + 2]); > + while (data.array[n + 2 + len]) > + len++; > + > + /* update length of callchain */ > + data.array[n] = len + 1; > + > + /* update sample ip with the first callchain entry */ > + if (ip_pos >= 0) > + data.array[ip_pos] = data.array[n + 2]; > + > + /* calculate sample callchain data array length */ > + n += len + 2; > + } > + /* TODO: handle more sample types */ > + > + size = n * sizeof(u64); > + data.hdr.size = size; > + bytes += size; > + > + if (perf_data_file__write(file, &data, size) < 0) { > + pr_err("failed to write perf data, error: %m\n"); > + return bytes; > + } > + > + prev = key; > + /* increase dummy timestamp to sort later samples */ > + tstamp++; > + } > + return bytes; > +} > diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c > new file mode 100644 > index 000000000000..5173ed882fdf > --- /dev/null > +++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c > @@ -0,0 +1,139 @@ > +// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) > +// Copyright (c) 2022 Google > +#include "vmlinux.h" > +#include <bpf/bpf_helpers.h> > +#include <bpf/bpf_tracing.h> > +#include <bpf/bpf_core_read.h> > + > +/* task->flags for off-cpu analysis */ > +#define PF_KTHREAD 0x00200000 /* I am a kernel thread */ > + > +/* task->state for off-cpu analysis */ > +#define TASK_INTERRUPTIBLE 0x0001 > +#define TASK_UNINTERRUPTIBLE 0x0002 > + > +#define MAX_STACKS 32 > +#define MAX_ENTRIES 102400 > + > +struct tstamp_data { > + __u32 stack_id; > + __u32 state; > + __u64 timestamp; > +}; > + > +struct offcpu_key { > + __u32 pid; > + __u32 tgid; > + __u32 stack_id; > + __u32 state; > +}; > + > +struct { > + __uint(type, BPF_MAP_TYPE_STACK_TRACE); > + __uint(key_size, sizeof(__u32)); > + __uint(value_size, MAX_STACKS * sizeof(__u64)); > + __uint(max_entries, MAX_ENTRIES); > +} stacks SEC(".maps"); > + > +struct { > + __uint(type, BPF_MAP_TYPE_TASK_STORAGE); > + __uint(map_flags, BPF_F_NO_PREALLOC); > + __type(key, int); > + __type(value, struct tstamp_data); > +} tstamp SEC(".maps"); > + > +struct { > + __uint(type, BPF_MAP_TYPE_HASH); > + __uint(key_size, sizeof(struct offcpu_key)); > + __uint(value_size, sizeof(__u64)); > + __uint(max_entries, MAX_ENTRIES); > +} off_cpu SEC(".maps"); > + > +/* old kernel task_struct definition */ > +struct task_struct___old { > + long state; > +} __attribute__((preserve_access_index)); > + > +int enabled = 0; > + > +/* > + * Old kernel used to call it task_struct->state and now it's '__state'. > + * Use BPF CO-RE "ignored suffix rule" to deal with it like below: > + * > + * https://nakryiko.com/posts/bpf-core-reference-guide/#handling-incompatible-field-and-type-changes > + */ > +static inline int get_task_state(struct task_struct *t) > +{ > + if (bpf_core_field_exists(t->__state)) > + return BPF_CORE_READ(t, __state); > + When building against a pre-5.14 kernel I'm running into a build issue here: tools/perf/util/bpf_skel/off_cpu.bpf.c:96:31: error: no member named '__ state' in 'struct task_struct'; did you mean 'state'? if (bpf_core_field_exists(t->__state)) ^~~~~~~ state This isn't covered by Andrii's BPF CO-RE reference guide. I have an #iffy workaround below,but this will be brittle if the 5.14+ kernel code is backported. Suggestions welcomed :-) Thanks, Ian ``` diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c index 792ae2847080..fb4fd3fbedd6 100644 --- a/tools/perf/util/bpf_skel/off_cpu.bpf.c +++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c @@ -71,10 +71,23 @@ struct { __uint(max_entries, 1); } cgroup_filter SEC(".maps"); +#if LINUX_VERSION_CODE >= KERNEL_VERSION(5,14,0) /* old kernel task_struct definition */ struct task_struct___old { long state; } __attribute__((preserve_access_index)); +#define TASK_STATE__STATE __state +#define ALT_TASK_STATE task_struct___old +#define ALT_TASK_STATE__STATE state +#else +/* new kernel task_struct definition */ +struct task_struct___new { + long __state; +} __attribute__((preserve_access_index)); +#define TASK_STATE__STATE state +#define ALT_TASK_STATE task_struct___new +#define ALT_TASK_STATE__STATE __state +#endif int enabled = 0; int has_cpu = 0; @@ -93,14 +106,14 @@ const volatile bool uses_cgroup_v1 = false; */ static inline int get_task_state(struct task_struct *t) { - if (bpf_core_field_exists(t->__state)) - return BPF_CORE_READ(t, __state); + if (bpf_core_field_exists(t->TASK_STATE__STATE)) + return BPF_CORE_READ(t, TASK_STATE__STATE); - /* recast pointer to capture task_struct___old type for compiler */ - struct task_struct___old *t_old = (void *)t; + /* recast pointer to capture task_struct___new/old type for compiler */ + struct ALT_TASK_STATE *t_alt = (void *)t; - /* now use old "state" name of the field */ - return BPF_CORE_READ(t_old, state); + /* now use new/old "state" name of the field */ + return BPF_CORE_READ(t_alt, ALT_TASK_STATE__STATE); } static inline __u64 get_cgroup_id(struct task_struct *t) ``` > + /* recast pointer to capture task_struct___old type for compiler */ > + struct task_struct___old *t_old = (void *)t; > + > + /* now use old "state" name of the field */ > + return BPF_CORE_READ(t_old, state); > +} > + > +SEC("tp_btf/sched_switch") > +int on_switch(u64 *ctx) > +{ > + __u64 ts; > + int state; > + __u32 stack_id; > + struct task_struct *prev, *next; > + struct tstamp_data *pelem; > + > + if (!enabled) > + return 0; > + > + prev = (struct task_struct *)ctx[1]; > + next = (struct task_struct *)ctx[2]; > + state = get_task_state(prev); > + > + ts = bpf_ktime_get_ns(); > + > + if (prev->flags & PF_KTHREAD) > + goto next; > + if (state != TASK_INTERRUPTIBLE && > + state != TASK_UNINTERRUPTIBLE) > + goto next; > + > + stack_id = bpf_get_stackid(ctx, &stacks, > + BPF_F_FAST_STACK_CMP | BPF_F_USER_STACK); > + > + pelem = bpf_task_storage_get(&tstamp, prev, NULL, > + BPF_LOCAL_STORAGE_GET_F_CREATE); > + if (!pelem) > + goto next; > + > + pelem->timestamp = ts; > + pelem->state = state; > + pelem->stack_id = stack_id; > + > +next: > + pelem = bpf_task_storage_get(&tstamp, next, NULL, 0); > + > + if (pelem && pelem->timestamp) { > + struct offcpu_key key = { > + .pid = next->pid, > + .tgid = next->tgid, > + .stack_id = pelem->stack_id, > + .state = pelem->state, > + }; > + __u64 delta = ts - pelem->timestamp; > + __u64 *total; > + > + total = bpf_map_lookup_elem(&off_cpu, &key); > + if (total) > + *total += delta; > + else > + bpf_map_update_elem(&off_cpu, &key, &delta, BPF_ANY); > + > + /* prevent to reuse the timestamp later */ > + pelem->timestamp = 0; > + } > + > + return 0; > +} > + > +char LICENSE[] SEC("license") = "Dual BSD/GPL"; > diff --git a/tools/perf/util/off_cpu.h b/tools/perf/util/off_cpu.h > new file mode 100644 > index 000000000000..375d03c424ea > --- /dev/null > +++ b/tools/perf/util/off_cpu.h > @@ -0,0 +1,24 @@ > +#ifndef PERF_UTIL_OFF_CPU_H > +#define PERF_UTIL_OFF_CPU_H > + > +struct evlist; > +struct perf_session; > + > +#define OFFCPU_EVENT "offcpu-time" > + > +#ifdef HAVE_BPF_SKEL > +int off_cpu_prepare(struct evlist *evlist); > +int off_cpu_write(struct perf_session *session); > +#else > +static inline int off_cpu_prepare(struct evlist *evlist __maybe_unused) > +{ > + return -1; > +} > + > +static inline int off_cpu_write(struct perf_session *session __maybe_unused) > +{ > + return -1; > +} > +#endif > + > +#endif /* PERF_UTIL_OFF_CPU_H */ > -- > 2.36.1.124.g0e6072fb45-goog >
On Tue, May 31, 2022 at 5:00 PM Ian Rogers <irogers@google.com> wrote: > > On Wed, May 18, 2022 at 3:47 PM Namhyung Kim <namhyung@kernel.org> wrote: [SNIP] > > + > > +/* > > + * Old kernel used to call it task_struct->state and now it's '__state'. > > + * Use BPF CO-RE "ignored suffix rule" to deal with it like below: > > + * > > + * https://nakryiko.com/posts/bpf-core-reference-guide/#handling-incompatible-field-and-type-changes > > + */ > > +static inline int get_task_state(struct task_struct *t) > > +{ > > + if (bpf_core_field_exists(t->__state)) > > + return BPF_CORE_READ(t, __state); > > + > > When building against a pre-5.14 kernel I'm running into a build issue here: > > tools/perf/util/bpf_skel/off_cpu.bpf.c:96:31: error: no member named '__ > state' in 'struct task_struct'; did you mean 'state'? > if (bpf_core_field_exists(t->__state)) > ^~~~~~~ > state > > This isn't covered by Andrii's BPF CO-RE reference guide. I have an > #iffy workaround below,but this will be brittle if the 5.14+ kernel > code is backported. Suggestions welcomed :-) Thanks for the fix. I think we should not guess the field name in the current task struct and check both versions separately. I'm afraid the version check won't work with some backported kernels. But do we care? Thanks, Namhyung
On Tue, May 31, 2022 at 11:01:14PM -0700, Namhyung Kim wrote: > On Tue, May 31, 2022 at 5:00 PM Ian Rogers <irogers@google.com> wrote: > > > > On Wed, May 18, 2022 at 3:47 PM Namhyung Kim <namhyung@kernel.org> wrote: > [SNIP] > > > + > > > +/* > > > + * Old kernel used to call it task_struct->state and now it's '__state'. > > > + * Use BPF CO-RE "ignored suffix rule" to deal with it like below: > > > + * > > > + * https://nakryiko.com/posts/bpf-core-reference-guide/#handling-incompatible-field-and-type-changes > > > + */ > > > +static inline int get_task_state(struct task_struct *t) > > > +{ > > > + if (bpf_core_field_exists(t->__state)) > > > + return BPF_CORE_READ(t, __state); > > > + > > > > When building against a pre-5.14 kernel I'm running into a build issue here: > > > > tools/perf/util/bpf_skel/off_cpu.bpf.c:96:31: error: no member named '__ > > state' in 'struct task_struct'; did you mean 'state'? > > if (bpf_core_field_exists(t->__state)) > > ^~~~~~~ > > state > > > > This isn't covered by Andrii's BPF CO-RE reference guide. I have an > > #iffy workaround below,but this will be brittle if the 5.14+ kernel > > code is backported. Suggestions welcomed :-) > > Thanks for the fix. I think we should not guess the field name > in the current task struct and check both versions separately. > I'm afraid the version check won't work with some backported > kernels. But do we care? What about this instead? ----8<---- From a621f836f00e11942e5d39a735ec8f7a21962d6a Mon Sep 17 00:00:00 2001 From: Namhyung Kim <namhyung@kernel.org> Date: Tue, 31 May 2022 14:25:05 -0700 Subject: [PATCH] perf tools: Fix a build failure in off-cpu BPF program on old kernels Old kernels have task_struct which contains "state" field. While the get_task_state() in the BPF code handles that, it assumed the kernel has the new definition and caused a build error on old kernels. We should not assume anything and access them carefully. Reported-by: Ian Rogers <irogers@google.com> Signed-off-by: Namhyung Kim <namhyung@kernel.org> --- tools/perf/util/bpf_skel/off_cpu.bpf.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-) diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c index 792ae2847080..cc6d7fd55118 100644 --- a/tools/perf/util/bpf_skel/off_cpu.bpf.c +++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c @@ -71,6 +71,11 @@ struct { __uint(max_entries, 1); } cgroup_filter SEC(".maps"); +/* new kernel task_struct definition */ +struct task_struct___new { + long __state; +} __attribute__((preserve_access_index)); + /* old kernel task_struct definition */ struct task_struct___old { long state; @@ -93,14 +98,17 @@ const volatile bool uses_cgroup_v1 = false; */ static inline int get_task_state(struct task_struct *t) { - if (bpf_core_field_exists(t->__state)) - return BPF_CORE_READ(t, __state); + /* recast pointer to capture new type for compiler */ + struct task_struct___new *t_new = (void *)t; - /* recast pointer to capture task_struct___old type for compiler */ - struct task_struct___old *t_old = (void *)t; + if (bpf_core_field_exists(t_new->__state)) { + return BPF_CORE_READ(t_new, __state); + } else { + /* recast pointer to capture old type for compiler */ + struct task_struct___old *t_old = (void *)t; - /* now use old "state" name of the field */ - return BPF_CORE_READ(t_old, state); + return BPF_CORE_READ(t_old, state); + } } static inline __u64 get_cgroup_id(struct task_struct *t)
diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt index 465be4e62a17..b4e9ef7edfef 100644 --- a/tools/perf/Documentation/perf-record.txt +++ b/tools/perf/Documentation/perf-record.txt @@ -758,6 +758,16 @@ include::intel-hybrid.txt[] If the URLs is not specified, the value of DEBUGINFOD_URLS system environment variable is used. +--off-cpu:: + Enable off-cpu profiling with BPF. The BPF program will collect + task scheduling information with (user) stacktrace and save them + as sample data of a software event named "offcpu-time". The + sample period will have the time the task slept in nanoseconds. + + Note that BPF can collect stack traces using frame pointer ("fp") + only, as of now. So the applications built without the frame + pointer might see bogus addresses. + SEE ALSO -------- linkperf:perf-stat[1], linkperf:perf-list[1], linkperf:perf-intel-pt[1] diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf index 6e5aded855cc..8f738e11356d 100644 --- a/tools/perf/Makefile.perf +++ b/tools/perf/Makefile.perf @@ -1038,6 +1038,7 @@ SKEL_TMP_OUT := $(abspath $(SKEL_OUT)/.tmp) SKELETONS := $(SKEL_OUT)/bpf_prog_profiler.skel.h SKELETONS += $(SKEL_OUT)/bperf_leader.skel.h $(SKEL_OUT)/bperf_follower.skel.h SKELETONS += $(SKEL_OUT)/bperf_cgroup.skel.h $(SKEL_OUT)/func_latency.skel.h +SKELETONS += $(SKEL_OUT)/off_cpu.skel.h $(SKEL_TMP_OUT) $(LIBBPF_OUTPUT): $(Q)$(MKDIR) -p $@ diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c index a5cf6a99d67f..91f88501412e 100644 --- a/tools/perf/builtin-record.c +++ b/tools/perf/builtin-record.c @@ -49,6 +49,7 @@ #include "util/clockid.h" #include "util/pmu-hybrid.h" #include "util/evlist-hybrid.h" +#include "util/off_cpu.h" #include "asm/bug.h" #include "perf.h" #include "cputopo.h" @@ -162,6 +163,7 @@ struct record { bool buildid_mmap; bool timestamp_filename; bool timestamp_boundary; + bool off_cpu; struct switch_output switch_output; unsigned long long samples; unsigned long output_max_size; /* = 0: unlimited */ @@ -903,6 +905,11 @@ static int record__config_text_poke(struct evlist *evlist) return 0; } +static int record__config_off_cpu(struct record *rec) +{ + return off_cpu_prepare(rec->evlist); +} + static bool record__kcore_readable(struct machine *machine) { char kcore[PATH_MAX]; @@ -2600,6 +2607,9 @@ static int __cmd_record(struct record *rec, int argc, const char **argv) } else status = err; + if (rec->off_cpu) + rec->bytes_written += off_cpu_write(rec->session); + record__synthesize(rec, true); /* this will be recalculated during process_buildids() */ rec->samples = 0; @@ -3324,6 +3334,7 @@ static struct option __record_options[] = { OPT_CALLBACK_OPTARG(0, "threads", &record.opts, NULL, "spec", "write collected trace data into several data files using parallel threads", record__parse_threads), + OPT_BOOLEAN(0, "off-cpu", &record.off_cpu, "Enable off-cpu analysis"), OPT_END() }; @@ -3743,6 +3754,12 @@ int cmd_record(int argc, const char **argv) set_nobuild('\0', "vmlinux", true); # undef set_nobuild # undef REASON +#endif + +#ifndef HAVE_BPF_SKEL +# define set_nobuild(s, l, m, c) set_option_nobuild(record_options, s, l, m, c) + set_nobuild('\0', "off-cpu", "no BUILD_BPF_SKEL=1", true); +# undef set_nobuild #endif rec->opts.affinity = PERF_AFFINITY_SYS; @@ -3981,6 +3998,14 @@ int cmd_record(int argc, const char **argv) } } + if (rec->off_cpu) { + err = record__config_off_cpu(rec); + if (err) { + pr_err("record__config_off_cpu failed, error %d\n", err); + goto out; + } + } + if (record_opts__config(&rec->opts)) { err = -EINVAL; goto out; diff --git a/tools/perf/util/Build b/tools/perf/util/Build index 9a7209a99e16..a51267d88ca9 100644 --- a/tools/perf/util/Build +++ b/tools/perf/util/Build @@ -147,6 +147,7 @@ perf-$(CONFIG_LIBBPF) += bpf_map.o perf-$(CONFIG_PERF_BPF_SKEL) += bpf_counter.o perf-$(CONFIG_PERF_BPF_SKEL) += bpf_counter_cgroup.o perf-$(CONFIG_PERF_BPF_SKEL) += bpf_ftrace.o +perf-$(CONFIG_PERF_BPF_SKEL) += bpf_off_cpu.o perf-$(CONFIG_BPF_PROLOGUE) += bpf-prologue.o perf-$(CONFIG_LIBELF) += symbol-elf.o perf-$(CONFIG_LIBELF) += probe-file.o diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c new file mode 100644 index 000000000000..9ed7aca3f4ac --- /dev/null +++ b/tools/perf/util/bpf_off_cpu.c @@ -0,0 +1,204 @@ +// SPDX-License-Identifier: GPL-2.0 +#include "util/bpf_counter.h" +#include "util/debug.h" +#include "util/evsel.h" +#include "util/evlist.h" +#include "util/off_cpu.h" +#include "util/perf-hooks.h" +#include "util/session.h" +#include <bpf/bpf.h> + +#include "bpf_skel/off_cpu.skel.h" + +#define MAX_STACKS 32 +/* we don't need actual timestamp, just want to put the samples at last */ +#define OFF_CPU_TIMESTAMP (~0ull << 32) + +static struct off_cpu_bpf *skel; + +struct off_cpu_key { + u32 pid; + u32 tgid; + u32 stack_id; + u32 state; +}; + +union off_cpu_data { + struct perf_event_header hdr; + u64 array[1024 / sizeof(u64)]; +}; + +static int off_cpu_config(struct evlist *evlist) +{ + struct evsel *evsel; + struct perf_event_attr attr = { + .type = PERF_TYPE_SOFTWARE, + .config = PERF_COUNT_SW_BPF_OUTPUT, + .size = sizeof(attr), /* to capture ABI version */ + }; + char *evname = strdup(OFFCPU_EVENT); + + if (evname == NULL) + return -ENOMEM; + + evsel = evsel__new(&attr); + if (!evsel) { + free(evname); + return -ENOMEM; + } + + evsel->core.attr.freq = 1; + evsel->core.attr.sample_period = 1; + /* off-cpu analysis depends on stack trace */ + evsel->core.attr.sample_type = PERF_SAMPLE_CALLCHAIN; + + evlist__add(evlist, evsel); + + free(evsel->name); + evsel->name = evname; + + return 0; +} + +static void off_cpu_start(void *arg __maybe_unused) +{ + skel->bss->enabled = 1; +} + +static void off_cpu_finish(void *arg __maybe_unused) +{ + skel->bss->enabled = 0; + off_cpu_bpf__destroy(skel); +} + +int off_cpu_prepare(struct evlist *evlist) +{ + int err; + + if (off_cpu_config(evlist) < 0) { + pr_err("Failed to config off-cpu BPF event\n"); + return -1; + } + + set_max_rlimit(); + + skel = off_cpu_bpf__open_and_load(); + if (!skel) { + pr_err("Failed to open off-cpu BPF skeleton\n"); + return -1; + } + + err = off_cpu_bpf__attach(skel); + if (err) { + pr_err("Failed to attach off-cpu BPF skeleton\n"); + goto out; + } + + if (perf_hooks__set_hook("record_start", off_cpu_start, NULL) || + perf_hooks__set_hook("record_end", off_cpu_finish, NULL)) { + pr_err("Failed to attach off-cpu skeleton\n"); + goto out; + } + + return 0; + +out: + off_cpu_bpf__destroy(skel); + return -1; +} + +int off_cpu_write(struct perf_session *session) +{ + int bytes = 0, size; + int fd, stack; + u64 sample_type, val, sid = 0; + struct evsel *evsel; + struct perf_data_file *file = &session->data->file; + struct off_cpu_key prev, key; + union off_cpu_data data = { + .hdr = { + .type = PERF_RECORD_SAMPLE, + .misc = PERF_RECORD_MISC_USER, + }, + }; + u64 tstamp = OFF_CPU_TIMESTAMP; + + skel->bss->enabled = 0; + + evsel = evlist__find_evsel_by_str(session->evlist, OFFCPU_EVENT); + if (evsel == NULL) { + pr_err("%s evsel not found\n", OFFCPU_EVENT); + return 0; + } + + sample_type = evsel->core.attr.sample_type; + + if (sample_type & (PERF_SAMPLE_ID | PERF_SAMPLE_IDENTIFIER)) { + if (evsel->core.id) + sid = evsel->core.id[0]; + } + + fd = bpf_map__fd(skel->maps.off_cpu); + stack = bpf_map__fd(skel->maps.stacks); + memset(&prev, 0, sizeof(prev)); + + while (!bpf_map_get_next_key(fd, &prev, &key)) { + int n = 1; /* start from perf_event_header */ + int ip_pos = -1; + + bpf_map_lookup_elem(fd, &key, &val); + + if (sample_type & PERF_SAMPLE_IDENTIFIER) + data.array[n++] = sid; + if (sample_type & PERF_SAMPLE_IP) { + ip_pos = n; + data.array[n++] = 0; /* will be updated */ + } + if (sample_type & PERF_SAMPLE_TID) + data.array[n++] = (u64)key.pid << 32 | key.tgid; + if (sample_type & PERF_SAMPLE_TIME) + data.array[n++] = tstamp; + if (sample_type & PERF_SAMPLE_ID) + data.array[n++] = sid; + if (sample_type & PERF_SAMPLE_CPU) + data.array[n++] = 0; + if (sample_type & PERF_SAMPLE_PERIOD) + data.array[n++] = val; + if (sample_type & PERF_SAMPLE_CALLCHAIN) { + int len = 0; + + /* data.array[n] is callchain->nr (updated later) */ + data.array[n + 1] = PERF_CONTEXT_USER; + data.array[n + 2] = 0; + + bpf_map_lookup_elem(stack, &key.stack_id, &data.array[n + 2]); + while (data.array[n + 2 + len]) + len++; + + /* update length of callchain */ + data.array[n] = len + 1; + + /* update sample ip with the first callchain entry */ + if (ip_pos >= 0) + data.array[ip_pos] = data.array[n + 2]; + + /* calculate sample callchain data array length */ + n += len + 2; + } + /* TODO: handle more sample types */ + + size = n * sizeof(u64); + data.hdr.size = size; + bytes += size; + + if (perf_data_file__write(file, &data, size) < 0) { + pr_err("failed to write perf data, error: %m\n"); + return bytes; + } + + prev = key; + /* increase dummy timestamp to sort later samples */ + tstamp++; + } + return bytes; +} diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c new file mode 100644 index 000000000000..5173ed882fdf --- /dev/null +++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c @@ -0,0 +1,139 @@ +// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) +// Copyright (c) 2022 Google +#include "vmlinux.h" +#include <bpf/bpf_helpers.h> +#include <bpf/bpf_tracing.h> +#include <bpf/bpf_core_read.h> + +/* task->flags for off-cpu analysis */ +#define PF_KTHREAD 0x00200000 /* I am a kernel thread */ + +/* task->state for off-cpu analysis */ +#define TASK_INTERRUPTIBLE 0x0001 +#define TASK_UNINTERRUPTIBLE 0x0002 + +#define MAX_STACKS 32 +#define MAX_ENTRIES 102400 + +struct tstamp_data { + __u32 stack_id; + __u32 state; + __u64 timestamp; +}; + +struct offcpu_key { + __u32 pid; + __u32 tgid; + __u32 stack_id; + __u32 state; +}; + +struct { + __uint(type, BPF_MAP_TYPE_STACK_TRACE); + __uint(key_size, sizeof(__u32)); + __uint(value_size, MAX_STACKS * sizeof(__u64)); + __uint(max_entries, MAX_ENTRIES); +} stacks SEC(".maps"); + +struct { + __uint(type, BPF_MAP_TYPE_TASK_STORAGE); + __uint(map_flags, BPF_F_NO_PREALLOC); + __type(key, int); + __type(value, struct tstamp_data); +} tstamp SEC(".maps"); + +struct { + __uint(type, BPF_MAP_TYPE_HASH); + __uint(key_size, sizeof(struct offcpu_key)); + __uint(value_size, sizeof(__u64)); + __uint(max_entries, MAX_ENTRIES); +} off_cpu SEC(".maps"); + +/* old kernel task_struct definition */ +struct task_struct___old { + long state; +} __attribute__((preserve_access_index)); + +int enabled = 0; + +/* + * Old kernel used to call it task_struct->state and now it's '__state'. + * Use BPF CO-RE "ignored suffix rule" to deal with it like below: + * + * https://nakryiko.com/posts/bpf-core-reference-guide/#handling-incompatible-field-and-type-changes + */ +static inline int get_task_state(struct task_struct *t) +{ + if (bpf_core_field_exists(t->__state)) + return BPF_CORE_READ(t, __state); + + /* recast pointer to capture task_struct___old type for compiler */ + struct task_struct___old *t_old = (void *)t; + + /* now use old "state" name of the field */ + return BPF_CORE_READ(t_old, state); +} + +SEC("tp_btf/sched_switch") +int on_switch(u64 *ctx) +{ + __u64 ts; + int state; + __u32 stack_id; + struct task_struct *prev, *next; + struct tstamp_data *pelem; + + if (!enabled) + return 0; + + prev = (struct task_struct *)ctx[1]; + next = (struct task_struct *)ctx[2]; + state = get_task_state(prev); + + ts = bpf_ktime_get_ns(); + + if (prev->flags & PF_KTHREAD) + goto next; + if (state != TASK_INTERRUPTIBLE && + state != TASK_UNINTERRUPTIBLE) + goto next; + + stack_id = bpf_get_stackid(ctx, &stacks, + BPF_F_FAST_STACK_CMP | BPF_F_USER_STACK); + + pelem = bpf_task_storage_get(&tstamp, prev, NULL, + BPF_LOCAL_STORAGE_GET_F_CREATE); + if (!pelem) + goto next; + + pelem->timestamp = ts; + pelem->state = state; + pelem->stack_id = stack_id; + +next: + pelem = bpf_task_storage_get(&tstamp, next, NULL, 0); + + if (pelem && pelem->timestamp) { + struct offcpu_key key = { + .pid = next->pid, + .tgid = next->tgid, + .stack_id = pelem->stack_id, + .state = pelem->state, + }; + __u64 delta = ts - pelem->timestamp; + __u64 *total; + + total = bpf_map_lookup_elem(&off_cpu, &key); + if (total) + *total += delta; + else + bpf_map_update_elem(&off_cpu, &key, &delta, BPF_ANY); + + /* prevent to reuse the timestamp later */ + pelem->timestamp = 0; + } + + return 0; +} + +char LICENSE[] SEC("license") = "Dual BSD/GPL"; diff --git a/tools/perf/util/off_cpu.h b/tools/perf/util/off_cpu.h new file mode 100644 index 000000000000..375d03c424ea --- /dev/null +++ b/tools/perf/util/off_cpu.h @@ -0,0 +1,24 @@ +#ifndef PERF_UTIL_OFF_CPU_H +#define PERF_UTIL_OFF_CPU_H + +struct evlist; +struct perf_session; + +#define OFFCPU_EVENT "offcpu-time" + +#ifdef HAVE_BPF_SKEL +int off_cpu_prepare(struct evlist *evlist); +int off_cpu_write(struct perf_session *session); +#else +static inline int off_cpu_prepare(struct evlist *evlist __maybe_unused) +{ + return -1; +} + +static inline int off_cpu_write(struct perf_session *session __maybe_unused) +{ + return -1; +} +#endif + +#endif /* PERF_UTIL_OFF_CPU_H */
Add --off-cpu option to enable the off-cpu profiling with BPF. It'd use a bpf_output event and rename it to "offcpu-time". Samples will be synthesized at the end of the record session using data from a BPF map which contains the aggregated off-cpu time at context switches. So it needs root privilege to get the off-cpu profiling. Each sample will have a separate user stacktrace so it will skip kernel threads. The sample ip will be set from the stacktrace and other sample data will be updated accordingly. Currently it only handles some basic sample types. The sample timestamp is set to a dummy value just not to bother with other events during the sorting. So it has a very big initial value and increase it on processing each samples. Good thing is that it can be used together with regular profiling like cpu cycles. If you don't want to that, you can use a dummy event to enable off-cpu profiling only. Example output: $ sudo perf record --off-cpu perf bench sched messaging -l 1000 $ sudo perf report --stdio --call-graph=no # Total Lost Samples: 0 # # Samples: 41K of event 'cycles' # Event count (approx.): 42137343851 ... # Samples: 1K of event 'offcpu-time' # Event count (approx.): 587990831640 # # Children Self Command Shared Object Symbol # ........ ........ ............... .................. ......................... # 81.66% 0.00% sched-messaging libc-2.33.so [.] __libc_start_main 81.66% 0.00% sched-messaging perf [.] cmd_bench 81.66% 0.00% sched-messaging perf [.] main 81.66% 0.00% sched-messaging perf [.] run_builtin 81.43% 0.00% sched-messaging perf [.] bench_sched_messaging 40.86% 40.86% sched-messaging libpthread-2.33.so [.] __read 37.66% 37.66% sched-messaging libpthread-2.33.so [.] __write 2.91% 2.91% sched-messaging libc-2.33.so [.] __poll ... As you can see it spent most of off-cpu time in read and write in bench_sched_messaging(). The --call-graph=no was added just to make the output concise here. It uses perf hooks facility to control BPF program during the record session rather than adding new BPF/off-cpu specific calls. Signed-off-by: Namhyung Kim <namhyung@kernel.org> --- tools/perf/Documentation/perf-record.txt | 10 ++ tools/perf/Makefile.perf | 1 + tools/perf/builtin-record.c | 25 +++ tools/perf/util/Build | 1 + tools/perf/util/bpf_off_cpu.c | 204 +++++++++++++++++++++++ tools/perf/util/bpf_skel/off_cpu.bpf.c | 139 +++++++++++++++ tools/perf/util/off_cpu.h | 24 +++ 7 files changed, 404 insertions(+) create mode 100644 tools/perf/util/bpf_off_cpu.c create mode 100644 tools/perf/util/bpf_skel/off_cpu.bpf.c create mode 100644 tools/perf/util/off_cpu.h