| Message ID | 20220506201627.85598-3-namhyung@kernel.org (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | BPF |
| Headers | show |
| Series | perf record: Implement off-cpu profiling with BPF (v2) | expand |
| Context | Check | Description |
|---|---|---|
| bpf/vmtest-bpf-next-VM_Test-2 | success | Logs for Kernel LATEST on z15 + selftests |
| bpf/vmtest-bpf-next-PR | success | PR summary |
| bpf/vmtest-bpf-next-VM_Test-1 | success | Logs for Kernel LATEST on ubuntu-latest + selftests |
| netdev/tree_selection | success | Not a local patch |
Em Fri, May 06, 2022 at 01:16:25PM -0700, Namhyung Kim escreveu: > 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 | 21 +++ > tools/perf/util/Build | 1 + > tools/perf/util/bpf_off_cpu.c | 208 +++++++++++++++++++++++ > tools/perf/util/bpf_skel/off_cpu.bpf.c | 139 +++++++++++++++ > tools/perf/util/off_cpu.h | 22 +++ > 7 files changed, 402 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..8084e3fb73a1 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 nano-second. nanoseconds. > + > + Note that BPF can collect stacktrace using frame pointer ("fp") stack traces > + only, as of now. So the applications built without the frame > + pointer might see bogus addresses. One possible improvement is to check if debugging info is available in the traced program and check if -fnoomit-frame-pointer is present: ⬢[acme@toolbox perf]$ readelf -wi ~/bin/perf | grep DW_AT_producer -m1 <d> DW_AT_producer : (indirect string, offset: 0x6627): GNU C99 11.2.1 20220127 (Red Hat 11.2.1-9) -mtune=generic -march=x86-64 -ggdb3 -O6 -std=gnu99 -fno-omit-frame-pointer -funwind-tables -fstack-protector-all ⬢[acme@toolbox perf]$ If debugging info is available and -fno-omit-frame-pointer isn't in the DW_AT_producer string, then we can print a flashing warning and even don't use the stack traces. That or some other more robust method to detect that frame pointers are valid. Some more comments below. > + > 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..4e0285ca9a2d 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 +3334,9 @@ 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), > +#ifdef HAVE_BPF_SKEL > + OPT_BOOLEAN(0, "off-cpu", &record.off_cpu, "Enable off-cpu analysis"), > +#endif Since this is in the documentation, I think we should have an #else clause and state that --off-cpu needs building with some specific make command line. > OPT_END() > }; > > @@ -3981,6 +3994,14 @@ 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..1f87d2a9b86d > --- /dev/null > +++ b/tools/perf/util/bpf_off_cpu.c > @@ -0,0 +1,208 @@ > +// 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; > + u64 cgroup_id; > +}; > + > +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 */ > + }; > + > + evsel = evsel__new(&attr); > + if (!evsel) > + 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 = strdup("offcpu-time"); > + if (evsel->name == NULL) > + return -ENOMEM; But at this point the evsel was left in the evlist? Shouldn't we start it all by trying to allocate this string and don't bother to call evsel__new() on failure, etc? > + > + 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 skeleton\n"); "BPF sleketon", to give a bit more context to users? > + return -1; > + } > + > + err = off_cpu_bpf__attach(skel); > + if (err) { > + pr_err("Failed to attach off-cpu skeleton\n"); Ditto. > + 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; > + bool found = false; > + 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; > + > + evlist__for_each_entry(session->evlist, evsel) { > + if (!strcmp(evsel__name(evsel), "offcpu-time")) { > + found = true; > + break; > + } > + } Don't we have some evlist__find_evsel function? struct evsel *evlist__find_evsel_by_str(struct evlist *evlist, const char *str) { struct evsel *evsel; evlist__for_each_entry(evlist, evsel) { if (!evsel->name) continue; if (strcmp(str, evsel->name) == 0) return evsel; } return NULL; } > + > + if (!found) { > + pr_err("offcpu-time evsel not found\n"); > + 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..4113bd19a2e4 > --- /dev/null > +++ b/tools/perf/util/off_cpu.h > @@ -0,0 +1,22 @@ > +#ifndef PERF_UTIL_OFF_CPU_H > +#define PERF_UTIL_OFF_CPU_H > + > +struct evlist; > +struct perf_session; > + > +#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 */ > -- > 2.36.0.512.ge40c2bad7a-goog
On Tue, May 10, 2022 at 10:02 AM Arnaldo Carvalho de Melo <acme@kernel.org> wrote: > > Em Fri, May 06, 2022 at 01:16:25PM -0700, Namhyung Kim escreveu: [SNIP] > > diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt > > index 465be4e62a17..8084e3fb73a1 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 nano-second. > > nanoseconds. ok > > + > > + Note that BPF can collect stacktrace using frame pointer ("fp") > > stack traces ok > > > + only, as of now. So the applications built without the frame > > + pointer might see bogus addresses. > > One possible improvement is to check if debugging info is available in > the traced program and check if -fnoomit-frame-pointer is present: > > ⬢[acme@toolbox perf]$ readelf -wi ~/bin/perf | grep DW_AT_producer -m1 > <d> DW_AT_producer : (indirect string, offset: 0x6627): GNU C99 11.2.1 20220127 (Red Hat 11.2.1-9) -mtune=generic -march=x86-64 -ggdb3 -O6 -std=gnu99 -fno-omit-frame-pointer -funwind-tables -fstack-protector-all > ⬢[acme@toolbox perf]$ > > If debugging info is available and -fno-omit-frame-pointer isn't in the > DW_AT_producer string, then we can print a flashing warning and even > don't use the stack traces. Yeah, but checking the binary only would not be enough as it will call other libraries. Also the libc would be the most frequent user of any sleeping syscalls, I guess. > > That or some other more robust method to detect that frame pointers are > valid. > > Some more comments below. > > > + > > 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..4e0285ca9a2d 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 +3334,9 @@ 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), > > +#ifdef HAVE_BPF_SKEL > > + OPT_BOOLEAN(0, "off-cpu", &record.off_cpu, "Enable off-cpu analysis"), > > +#endif > > > Since this is in the documentation, I think we should have an #else > clause and state that --off-cpu needs building with some specific make > command line. I'd rather remove the #ifdef here and put it after parse_options to show the warning. > > > OPT_END() > > }; > > > > @@ -3981,6 +3994,14 @@ 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..1f87d2a9b86d > > --- /dev/null > > +++ b/tools/perf/util/bpf_off_cpu.c > > @@ -0,0 +1,208 @@ > > +// 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; > > + u64 cgroup_id; > > +}; > > + > > +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 */ > > + }; > > + > > + evsel = evsel__new(&attr); > > + if (!evsel) > > + 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 = strdup("offcpu-time"); > > + if (evsel->name == NULL) > > + return -ENOMEM; > > But at this point the evsel was left in the evlist? Shouldn't we start > it all by trying to allocate this string and don't bother to call > evsel__new() on failure, etc? Sounds good, will change. > > > + > > + 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 skeleton\n"); > > "BPF sleketon", to give a bit more context to users? ok > > > + return -1; > > + } > > + > > + err = off_cpu_bpf__attach(skel); > > + if (err) { > > + pr_err("Failed to attach off-cpu skeleton\n"); > > Ditto. ok > > > + 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; > > + bool found = false; > > + 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; > > + > > + evlist__for_each_entry(session->evlist, evsel) { > > + if (!strcmp(evsel__name(evsel), "offcpu-time")) { > > + found = true; > > + break; > > + } > > + } > > Don't we have some evlist__find_evsel function? > > struct evsel *evlist__find_evsel_by_str(struct evlist *evlist, const char *str) > { > struct evsel *evsel; > > evlist__for_each_entry(evlist, evsel) { > if (!evsel->name) > continue; > if (strcmp(str, evsel->name) == 0) > return evsel; > } > > return NULL; > } Nice, I'll use it instead. Thanks for your review! Namhyung
diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt index 465be4e62a17..8084e3fb73a1 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 nano-second. + + Note that BPF can collect stacktrace 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..4e0285ca9a2d 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 +3334,9 @@ 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), +#ifdef HAVE_BPF_SKEL + OPT_BOOLEAN(0, "off-cpu", &record.off_cpu, "Enable off-cpu analysis"), +#endif OPT_END() }; @@ -3981,6 +3994,14 @@ 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..1f87d2a9b86d --- /dev/null +++ b/tools/perf/util/bpf_off_cpu.c @@ -0,0 +1,208 @@ +// 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; + u64 cgroup_id; +}; + +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 */ + }; + + evsel = evsel__new(&attr); + if (!evsel) + 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 = strdup("offcpu-time"); + if (evsel->name == NULL) + return -ENOMEM; + + 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 skeleton\n"); + return -1; + } + + err = off_cpu_bpf__attach(skel); + if (err) { + pr_err("Failed to attach off-cpu 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; + bool found = false; + 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; + + evlist__for_each_entry(session->evlist, evsel) { + if (!strcmp(evsel__name(evsel), "offcpu-time")) { + found = true; + break; + } + } + + if (!found) { + pr_err("offcpu-time evsel not found\n"); + 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..4113bd19a2e4 --- /dev/null +++ b/tools/perf/util/off_cpu.h @@ -0,0 +1,22 @@ +#ifndef PERF_UTIL_OFF_CPU_H +#define PERF_UTIL_OFF_CPU_H + +struct evlist; +struct perf_session; + +#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 | 21 +++ tools/perf/util/Build | 1 + tools/perf/util/bpf_off_cpu.c | 208 +++++++++++++++++++++++ tools/perf/util/bpf_skel/off_cpu.bpf.c | 139 +++++++++++++++ tools/perf/util/off_cpu.h | 22 +++ 7 files changed, 402 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