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>

1 files changed, 72 insertions, 0 deletions

diff --git a/tools/perf/util/bpf_counter.h b/tools/perf/util/bpf_counter.h
new file mode 100644
index 000000000000..2eca210e5dc1
--- /dev/null
+++ b/tools/perf/util/bpf_counter.h
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_BPF_COUNTER_H
+#define __PERF_BPF_COUNTER_H 1
+
+#include <linux/list.h>
+
+struct evsel;
+struct target;
+struct bpf_counter;
+
+typedef int (*bpf_counter_evsel_op)(struct evsel *evsel);
+typedef int (*bpf_counter_evsel_target_op)(struct evsel *evsel,
+					   struct target *target);
+typedef int (*bpf_counter_evsel_install_pe_op)(struct evsel *evsel,
+					       int cpu,
+					       int fd);
+
+struct bpf_counter_ops {
+	bpf_counter_evsel_target_op load;
+	bpf_counter_evsel_op enable;
+	bpf_counter_evsel_op read;
+	bpf_counter_evsel_op destroy;
+	bpf_counter_evsel_install_pe_op install_pe;
+};
+
+struct bpf_counter {
+	void *skel;
+	struct list_head list;
+};
+
+#ifdef HAVE_BPF_SKEL
+
+int bpf_counter__load(struct evsel *evsel, struct target *target);
+int bpf_counter__enable(struct evsel *evsel);
+int bpf_counter__read(struct evsel *evsel);
+void bpf_counter__destroy(struct evsel *evsel);
+int bpf_counter__install_pe(struct evsel *evsel, int cpu, int fd);
+
+#else /* HAVE_BPF_SKEL */
+
+#include<linux/err.h>
+
+static inline int bpf_counter__load(struct evsel *evsel __maybe_unused,
+				    struct target *target __maybe_unused)
+{
+	return 0;
+}
+
+static inline int bpf_counter__enable(struct evsel *evsel __maybe_unused)
+{
+	return 0;
+}
+
+static inline int bpf_counter__read(struct evsel *evsel __maybe_unused)
+{
+	return -EAGAIN;
+}
+
+static inline void bpf_counter__destroy(struct evsel *evsel __maybe_unused)
+{
+}
+
+static inline int bpf_counter__install_pe(struct evsel *evsel __maybe_unused,
+					  int cpu __maybe_unused,
+					  int fd __maybe_unused)
+{
+	return 0;
+}
+
+#endif /* HAVE_BPF_SKEL */
+
+#endif /* __PERF_BPF_COUNTER_H */