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author | Song Liu <songliubraving@fb.com> | 2020-12-30 00:42:14 +0300 |
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committer | Arnaldo Carvalho de Melo <acme@redhat.com> | 2021-01-20 20:25:28 +0300 |
commit | fa853c4b839ece9cd589e8858819240933cc4d78 (patch) | |
tree | b1cfceea97cad873a3a5d1642e1c2f3e195e0314 /tools/perf/util/bpf_skel | |
parent | fbcdaa1908e8f61aa56c71a1db9a9deb72110a9d (diff) | |
download | linux-fa853c4b839ece9cd589e8858819240933cc4d78.tar.xz |
perf stat: Enable counting events for BPF programs
Introduce 'perf stat -b' option, which counts events for BPF programs, like:
[root@localhost ~]# ~/perf stat -e ref-cycles,cycles -b 254 -I 1000
1.487903822 115,200 ref-cycles
1.487903822 86,012 cycles
2.489147029 80,560 ref-cycles
2.489147029 73,784 cycles
3.490341825 60,720 ref-cycles
3.490341825 37,797 cycles
4.491540887 37,120 ref-cycles
4.491540887 31,963 cycles
The example above counts 'cycles' and 'ref-cycles' of BPF program of id
254. This is similar to bpftool-prog-profile command, but more
flexible.
'perf stat -b' creates per-cpu perf_event and loads fentry/fexit BPF
programs (monitor-progs) to the target BPF program (target-prog). The
monitor-progs read perf_event before and after the target-prog, and
aggregate the difference in a BPF map. Then the user space reads data
from these maps.
A new 'struct bpf_counter' is introduced to provide a common interface
that uses BPF programs/maps to count perf events.
Committer notes:
Removed all but bpf_counter.h includes from evsel.h, not needed at all.
Also BPF map lookups for PERCPU_ARRAYs need to have as its value receive
buffer passed to the kernel libbpf_num_possible_cpus() entries, not
evsel__nr_cpus(evsel), as the former uses
/sys/devices/system/cpu/possible while the later uses
/sys/devices/system/cpu/online, which may be less than the 'possible'
number making the bpf map lookup overwrite memory and cause hard to
debug memory corruption.
We need to continue using evsel__nr_cpus(evsel) when accessing the
perf_counts array tho, not to overwrite another are of memory :-)
Signed-off-by: Song Liu <songliubraving@fb.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/lkml/20210120163031.GU12699@kernel.org/
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: kernel-team@fb.com
Link: http://lore.kernel.org/lkml/20201229214214.3413833-4-songliubraving@fb.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools/perf/util/bpf_skel')
-rw-r--r-- | tools/perf/util/bpf_skel/bpf_prog_profiler.bpf.c | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/tools/perf/util/bpf_skel/bpf_prog_profiler.bpf.c b/tools/perf/util/bpf_skel/bpf_prog_profiler.bpf.c new file mode 100644 index 000000000000..c7cec92d0236 --- /dev/null +++ b/tools/perf/util/bpf_skel/bpf_prog_profiler.bpf.c @@ -0,0 +1,93 @@ +// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) +// Copyright (c) 2020 Facebook +#include <linux/bpf.h> +#include <bpf/bpf_helpers.h> +#include <bpf/bpf_tracing.h> + +/* map of perf event fds, num_cpu * num_metric entries */ +struct { + __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY); + __uint(key_size, sizeof(__u32)); + __uint(value_size, sizeof(int)); +} events SEC(".maps"); + +/* readings at fentry */ +struct { + __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY); + __uint(key_size, sizeof(__u32)); + __uint(value_size, sizeof(struct bpf_perf_event_value)); + __uint(max_entries, 1); +} fentry_readings SEC(".maps"); + +/* accumulated readings */ +struct { + __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY); + __uint(key_size, sizeof(__u32)); + __uint(value_size, sizeof(struct bpf_perf_event_value)); + __uint(max_entries, 1); +} accum_readings SEC(".maps"); + +const volatile __u32 num_cpu = 1; + +SEC("fentry/XXX") +int BPF_PROG(fentry_XXX) +{ + __u32 key = bpf_get_smp_processor_id(); + struct bpf_perf_event_value *ptr; + __u32 zero = 0; + long err; + + /* look up before reading, to reduce error */ + ptr = bpf_map_lookup_elem(&fentry_readings, &zero); + if (!ptr) + return 0; + + err = bpf_perf_event_read_value(&events, key, ptr, sizeof(*ptr)); + if (err) + return 0; + + return 0; +} + +static inline void +fexit_update_maps(struct bpf_perf_event_value *after) +{ + struct bpf_perf_event_value *before, diff, *accum; + __u32 zero = 0; + + before = bpf_map_lookup_elem(&fentry_readings, &zero); + /* only account samples with a valid fentry_reading */ + if (before && before->counter) { + struct bpf_perf_event_value *accum; + + diff.counter = after->counter - before->counter; + diff.enabled = after->enabled - before->enabled; + diff.running = after->running - before->running; + + accum = bpf_map_lookup_elem(&accum_readings, &zero); + if (accum) { + accum->counter += diff.counter; + accum->enabled += diff.enabled; + accum->running += diff.running; + } + } +} + +SEC("fexit/XXX") +int BPF_PROG(fexit_XXX) +{ + struct bpf_perf_event_value reading; + __u32 cpu = bpf_get_smp_processor_id(); + __u32 one = 1, zero = 0; + int err; + + /* read all events before updating the maps, to reduce error */ + err = bpf_perf_event_read_value(&events, cpu, &reading, sizeof(reading)); + if (err) + return 0; + + fexit_update_maps(&reading); + return 0; +} + +char LICENSE[] SEC("license") = "Dual BSD/GPL"; |