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fa853c4b83
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>
94 lines
2.3 KiB
C
94 lines
2.3 KiB
C
// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
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// Copyright (c) 2020 Facebook
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#include <linux/bpf.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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/* map of perf event fds, num_cpu * num_metric entries */
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struct {
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__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
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__uint(key_size, sizeof(__u32));
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__uint(value_size, sizeof(int));
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} events SEC(".maps");
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/* readings at fentry */
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struct {
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__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
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__uint(key_size, sizeof(__u32));
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__uint(value_size, sizeof(struct bpf_perf_event_value));
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__uint(max_entries, 1);
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} fentry_readings SEC(".maps");
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/* accumulated readings */
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struct {
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__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
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__uint(key_size, sizeof(__u32));
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__uint(value_size, sizeof(struct bpf_perf_event_value));
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__uint(max_entries, 1);
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} accum_readings SEC(".maps");
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const volatile __u32 num_cpu = 1;
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SEC("fentry/XXX")
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int BPF_PROG(fentry_XXX)
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{
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__u32 key = bpf_get_smp_processor_id();
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struct bpf_perf_event_value *ptr;
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__u32 zero = 0;
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long err;
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/* look up before reading, to reduce error */
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ptr = bpf_map_lookup_elem(&fentry_readings, &zero);
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if (!ptr)
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return 0;
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err = bpf_perf_event_read_value(&events, key, ptr, sizeof(*ptr));
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if (err)
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return 0;
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return 0;
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}
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static inline void
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fexit_update_maps(struct bpf_perf_event_value *after)
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{
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struct bpf_perf_event_value *before, diff, *accum;
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__u32 zero = 0;
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before = bpf_map_lookup_elem(&fentry_readings, &zero);
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/* only account samples with a valid fentry_reading */
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if (before && before->counter) {
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struct bpf_perf_event_value *accum;
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diff.counter = after->counter - before->counter;
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diff.enabled = after->enabled - before->enabled;
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diff.running = after->running - before->running;
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accum = bpf_map_lookup_elem(&accum_readings, &zero);
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if (accum) {
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accum->counter += diff.counter;
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accum->enabled += diff.enabled;
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accum->running += diff.running;
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}
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}
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}
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SEC("fexit/XXX")
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int BPF_PROG(fexit_XXX)
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{
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struct bpf_perf_event_value reading;
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__u32 cpu = bpf_get_smp_processor_id();
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__u32 one = 1, zero = 0;
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int err;
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/* read all events before updating the maps, to reduce error */
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err = bpf_perf_event_read_value(&events, cpu, &reading, sizeof(reading));
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if (err)
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return 0;
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fexit_update_maps(&reading);
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return 0;
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}
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char LICENSE[] SEC("license") = "Dual BSD/GPL";
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