Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 819 insertions, 0 deletions

diff --git a/tools/perf/util/bpf_counter.c b/tools/perf/util/bpf_counter.c
new file mode 100644
index 0000000000..6732cbbcf9
--- /dev/null
+++ b/tools/perf/util/bpf_counter.c
@@ -0,0 +1,819 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/* Copyright (c) 2019 Facebook */
+
+#include <assert.h>
+#include <limits.h>
+#include <unistd.h>
+#include <sys/file.h>
+#include <sys/time.h>
+#include <linux/err.h>
+#include <linux/zalloc.h>
+#include <api/fs/fs.h>
+#include <perf/bpf_perf.h>
+
+#include "bpf_counter.h"
+#include "bpf-utils.h"
+#include "counts.h"
+#include "debug.h"
+#include "evsel.h"
+#include "evlist.h"
+#include "target.h"
+#include "cgroup.h"
+#include "cpumap.h"
+#include "thread_map.h"
+
+#include "bpf_skel/bpf_prog_profiler.skel.h"
+#include "bpf_skel/bperf_u.h"
+#include "bpf_skel/bperf_leader.skel.h"
+#include "bpf_skel/bperf_follower.skel.h"
+
+#define ATTR_MAP_SIZE 16
+
+static inline void *u64_to_ptr(__u64 ptr)
+{
+	return (void *)(unsigned long)ptr;
+}
+
+static struct bpf_counter *bpf_counter_alloc(void)
+{
+	struct bpf_counter *counter;
+
+	counter = zalloc(sizeof(*counter));
+	if (counter)
+		INIT_LIST_HEAD(&counter->list);
+	return counter;
+}
+
+static int bpf_program_profiler__destroy(struct evsel *evsel)
+{
+	struct bpf_counter *counter, *tmp;
+
+	list_for_each_entry_safe(counter, tmp,
+				 &evsel->bpf_counter_list, list) {
+		list_del_init(&counter->list);
+		bpf_prog_profiler_bpf__destroy(counter->skel);
+		free(counter);
+	}
+	assert(list_empty(&evsel->bpf_counter_list));
+
+	return 0;
+}
+
+static char *bpf_target_prog_name(int tgt_fd)
+{
+	struct bpf_func_info *func_info;
+	struct perf_bpil *info_linear;
+	const struct btf_type *t;
+	struct btf *btf = NULL;
+	char *name = NULL;
+
+	info_linear = get_bpf_prog_info_linear(tgt_fd, 1UL << PERF_BPIL_FUNC_INFO);
+	if (IS_ERR_OR_NULL(info_linear)) {
+		pr_debug("failed to get info_linear for prog FD %d\n", tgt_fd);
+		return NULL;
+	}
+
+	if (info_linear->info.btf_id == 0) {
+		pr_debug("prog FD %d doesn't have valid btf\n", tgt_fd);
+		goto out;
+	}
+
+	btf = btf__load_from_kernel_by_id(info_linear->info.btf_id);
+	if (libbpf_get_error(btf)) {
+		pr_debug("failed to load btf for prog FD %d\n", tgt_fd);
+		goto out;
+	}
+
+	func_info = u64_to_ptr(info_linear->info.func_info);
+	t = btf__type_by_id(btf, func_info[0].type_id);
+	if (!t) {
+		pr_debug("btf %d doesn't have type %d\n",
+			 info_linear->info.btf_id, func_info[0].type_id);
+		goto out;
+	}
+	name = strdup(btf__name_by_offset(btf, t->name_off));
+out:
+	btf__free(btf);
+	free(info_linear);
+	return name;
+}
+
+static int bpf_program_profiler_load_one(struct evsel *evsel, u32 prog_id)
+{
+	struct bpf_prog_profiler_bpf *skel;
+	struct bpf_counter *counter;
+	struct bpf_program *prog;
+	char *prog_name;
+	int prog_fd;
+	int err;
+
+	prog_fd = bpf_prog_get_fd_by_id(prog_id);
+	if (prog_fd < 0) {
+		pr_err("Failed to open fd for bpf prog %u\n", prog_id);
+		return -1;
+	}
+	counter = bpf_counter_alloc();
+	if (!counter) {
+		close(prog_fd);
+		return -1;
+	}
+
+	skel = bpf_prog_profiler_bpf__open();
+	if (!skel) {
+		pr_err("Failed to open bpf skeleton\n");
+		goto err_out;
+	}
+
+	skel->rodata->num_cpu = evsel__nr_cpus(evsel);
+
+	bpf_map__set_max_entries(skel->maps.events, evsel__nr_cpus(evsel));
+	bpf_map__set_max_entries(skel->maps.fentry_readings, 1);
+	bpf_map__set_max_entries(skel->maps.accum_readings, 1);
+
+	prog_name = bpf_target_prog_name(prog_fd);
+	if (!prog_name) {
+		pr_err("Failed to get program name for bpf prog %u. Does it have BTF?\n", prog_id);
+		goto err_out;
+	}
+
+	bpf_object__for_each_program(prog, skel->obj) {
+		err = bpf_program__set_attach_target(prog, prog_fd, prog_name);
+		if (err) {
+			pr_err("bpf_program__set_attach_target failed.\n"
+			       "Does bpf prog %u have BTF?\n", prog_id);
+			goto err_out;
+		}
+	}
+	set_max_rlimit();
+	err = bpf_prog_profiler_bpf__load(skel);
+	if (err) {
+		pr_err("bpf_prog_profiler_bpf__load failed\n");
+		goto err_out;
+	}
+
+	assert(skel != NULL);
+	counter->skel = skel;
+	list_add(&counter->list, &evsel->bpf_counter_list);
+	close(prog_fd);
+	return 0;
+err_out:
+	bpf_prog_profiler_bpf__destroy(skel);
+	free(counter);
+	close(prog_fd);
+	return -1;
+}
+
+static int bpf_program_profiler__load(struct evsel *evsel, struct target *target)
+{
+	char *bpf_str, *bpf_str_, *tok, *saveptr = NULL, *p;
+	u32 prog_id;
+	int ret;
+
+	bpf_str_ = bpf_str = strdup(target->bpf_str);
+	if (!bpf_str)
+		return -1;
+
+	while ((tok = strtok_r(bpf_str, ",", &saveptr)) != NULL) {
+		prog_id = strtoul(tok, &p, 10);
+		if (prog_id == 0 || prog_id == UINT_MAX ||
+		    (*p != '\0' && *p != ',')) {
+			pr_err("Failed to parse bpf prog ids %s\n",
+			       target->bpf_str);
+			return -1;
+		}
+
+		ret = bpf_program_profiler_load_one(evsel, prog_id);
+		if (ret) {
+			bpf_program_profiler__destroy(evsel);
+			free(bpf_str_);
+			return -1;
+		}
+		bpf_str = NULL;
+	}
+	free(bpf_str_);
+	return 0;
+}
+
+static int bpf_program_profiler__enable(struct evsel *evsel)
+{
+	struct bpf_counter *counter;
+	int ret;
+
+	list_for_each_entry(counter, &evsel->bpf_counter_list, list) {
+		assert(counter->skel != NULL);
+		ret = bpf_prog_profiler_bpf__attach(counter->skel);
+		if (ret) {
+			bpf_program_profiler__destroy(evsel);
+			return ret;
+		}
+	}
+	return 0;
+}
+
+static int bpf_program_profiler__disable(struct evsel *evsel)
+{
+	struct bpf_counter *counter;
+
+	list_for_each_entry(counter, &evsel->bpf_counter_list, list) {
+		assert(counter->skel != NULL);
+		bpf_prog_profiler_bpf__detach(counter->skel);
+	}
+	return 0;
+}
+
+static int bpf_program_profiler__read(struct evsel *evsel)
+{
+	// BPF_MAP_TYPE_PERCPU_ARRAY uses /sys/devices/system/cpu/possible
+	// Sometimes possible > online, like on a Ryzen 3900X that has 24
+	// threads but its possible showed 0-31 -acme
+	int num_cpu_bpf = libbpf_num_possible_cpus();
+	struct bpf_perf_event_value values[num_cpu_bpf];
+	struct bpf_counter *counter;
+	struct perf_counts_values *counts;
+	int reading_map_fd;
+	__u32 key = 0;
+	int err, idx, bpf_cpu;
+
+	if (list_empty(&evsel->bpf_counter_list))
+		return -EAGAIN;
+
+	perf_cpu_map__for_each_idx(idx, evsel__cpus(evsel)) {
+		counts = perf_counts(evsel->counts, idx, 0);
+		counts->val = 0;
+		counts->ena = 0;
+		counts->run = 0;
+	}
+	list_for_each_entry(counter, &evsel->bpf_counter_list, list) {
+		struct bpf_prog_profiler_bpf *skel = counter->skel;
+
+		assert(skel != NULL);
+		reading_map_fd = bpf_map__fd(skel->maps.accum_readings);
+
+		err = bpf_map_lookup_elem(reading_map_fd, &key, values);
+		if (err) {
+			pr_err("failed to read value\n");
+			return err;
+		}
+
+		for (bpf_cpu = 0; bpf_cpu < num_cpu_bpf; bpf_cpu++) {
+			idx = perf_cpu_map__idx(evsel__cpus(evsel),
+						(struct perf_cpu){.cpu = bpf_cpu});
+			if (idx == -1)
+				continue;
+			counts = perf_counts(evsel->counts, idx, 0);
+			counts->val += values[bpf_cpu].counter;
+			counts->ena += values[bpf_cpu].enabled;
+			counts->run += values[bpf_cpu].running;
+		}
+	}
+	return 0;
+}
+
+static int bpf_program_profiler__install_pe(struct evsel *evsel, int cpu_map_idx,
+					    int fd)
+{
+	struct bpf_prog_profiler_bpf *skel;
+	struct bpf_counter *counter;
+	int ret;
+
+	list_for_each_entry(counter, &evsel->bpf_counter_list, list) {
+		skel = counter->skel;
+		assert(skel != NULL);
+
+		ret = bpf_map_update_elem(bpf_map__fd(skel->maps.events),
+					  &cpu_map_idx, &fd, BPF_ANY);
+		if (ret)
+			return ret;
+	}
+	return 0;
+}
+
+struct bpf_counter_ops bpf_program_profiler_ops = {
+	.load       = bpf_program_profiler__load,
+	.enable	    = bpf_program_profiler__enable,
+	.disable    = bpf_program_profiler__disable,
+	.read       = bpf_program_profiler__read,
+	.destroy    = bpf_program_profiler__destroy,
+	.install_pe = bpf_program_profiler__install_pe,
+};
+
+static bool bperf_attr_map_compatible(int attr_map_fd)
+{
+	struct bpf_map_info map_info = {0};
+	__u32 map_info_len = sizeof(map_info);
+	int err;
+
+	err = bpf_obj_get_info_by_fd(attr_map_fd, &map_info, &map_info_len);
+
+	if (err)
+		return false;
+	return (map_info.key_size == sizeof(struct perf_event_attr)) &&
+		(map_info.value_size == sizeof(struct perf_event_attr_map_entry));
+}
+
+static int bperf_lock_attr_map(struct target *target)
+{
+	char path[PATH_MAX];
+	int map_fd, err;
+
+	if (target->attr_map) {
+		scnprintf(path, PATH_MAX, "%s", target->attr_map);
+	} else {
+		scnprintf(path, PATH_MAX, "%s/fs/bpf/%s", sysfs__mountpoint(),
+			  BPF_PERF_DEFAULT_ATTR_MAP_PATH);
+	}
+
+	if (access(path, F_OK)) {
+		map_fd = bpf_map_create(BPF_MAP_TYPE_HASH, NULL,
+					sizeof(struct perf_event_attr),
+					sizeof(struct perf_event_attr_map_entry),
+					ATTR_MAP_SIZE, NULL);
+		if (map_fd < 0)
+			return -1;
+
+		err = bpf_obj_pin(map_fd, path);
+		if (err) {
+			/* someone pinned the map in parallel? */
+			close(map_fd);
+			map_fd = bpf_obj_get(path);
+			if (map_fd < 0)
+				return -1;
+		}
+	} else {
+		map_fd = bpf_obj_get(path);
+		if (map_fd < 0)
+			return -1;
+	}
+
+	if (!bperf_attr_map_compatible(map_fd)) {
+		close(map_fd);
+		return -1;
+
+	}
+	err = flock(map_fd, LOCK_EX);
+	if (err) {
+		close(map_fd);
+		return -1;
+	}
+	return map_fd;
+}
+
+static int bperf_check_target(struct evsel *evsel,
+			      struct target *target,
+			      enum bperf_filter_type *filter_type,
+			      __u32 *filter_entry_cnt)
+{
+	if (evsel->core.leader->nr_members > 1) {
+		pr_err("bpf managed perf events do not yet support groups.\n");
+		return -1;
+	}
+
+	/* determine filter type based on target */
+	if (target->system_wide) {
+		*filter_type = BPERF_FILTER_GLOBAL;
+		*filter_entry_cnt = 1;
+	} else if (target->cpu_list) {
+		*filter_type = BPERF_FILTER_CPU;
+		*filter_entry_cnt = perf_cpu_map__nr(evsel__cpus(evsel));
+	} else if (target->tid) {
+		*filter_type = BPERF_FILTER_PID;
+		*filter_entry_cnt = perf_thread_map__nr(evsel->core.threads);
+	} else if (target->pid || evsel->evlist->workload.pid != -1) {
+		*filter_type = BPERF_FILTER_TGID;
+		*filter_entry_cnt = perf_thread_map__nr(evsel->core.threads);
+	} else {
+		pr_err("bpf managed perf events do not yet support these targets.\n");
+		return -1;
+	}
+
+	return 0;
+}
+
+static	struct perf_cpu_map *all_cpu_map;
+
+static int bperf_reload_leader_program(struct evsel *evsel, int attr_map_fd,
+				       struct perf_event_attr_map_entry *entry)
+{
+	struct bperf_leader_bpf *skel = bperf_leader_bpf__open();
+	int link_fd, diff_map_fd, err;
+	struct bpf_link *link = NULL;
+
+	if (!skel) {
+		pr_err("Failed to open leader skeleton\n");
+		return -1;
+	}
+
+	bpf_map__set_max_entries(skel->maps.events, libbpf_num_possible_cpus());
+	err = bperf_leader_bpf__load(skel);
+	if (err) {
+		pr_err("Failed to load leader skeleton\n");
+		goto out;
+	}
+
+	link = bpf_program__attach(skel->progs.on_switch);
+	if (IS_ERR(link)) {
+		pr_err("Failed to attach leader program\n");
+		err = PTR_ERR(link);
+		goto out;
+	}
+
+	link_fd = bpf_link__fd(link);
+	diff_map_fd = bpf_map__fd(skel->maps.diff_readings);
+	entry->link_id = bpf_link_get_id(link_fd);
+	entry->diff_map_id = bpf_map_get_id(diff_map_fd);
+	err = bpf_map_update_elem(attr_map_fd, &evsel->core.attr, entry, BPF_ANY);
+	assert(err == 0);
+
+	evsel->bperf_leader_link_fd = bpf_link_get_fd_by_id(entry->link_id);
+	assert(evsel->bperf_leader_link_fd >= 0);
+
+	/*
+	 * save leader_skel for install_pe, which is called within
+	 * following evsel__open_per_cpu call
+	 */
+	evsel->leader_skel = skel;
+	evsel__open_per_cpu(evsel, all_cpu_map, -1);
+
+out:
+	bperf_leader_bpf__destroy(skel);
+	bpf_link__destroy(link);
+	return err;
+}
+
+static int bperf__load(struct evsel *evsel, struct target *target)
+{
+	struct perf_event_attr_map_entry entry = {0xffffffff, 0xffffffff};
+	int attr_map_fd, diff_map_fd = -1, err;
+	enum bperf_filter_type filter_type;
+	__u32 filter_entry_cnt, i;
+
+	if (bperf_check_target(evsel, target, &filter_type, &filter_entry_cnt))
+		return -1;
+
+	if (!all_cpu_map) {
+		all_cpu_map = perf_cpu_map__new(NULL);
+		if (!all_cpu_map)
+			return -1;
+	}
+
+	evsel->bperf_leader_prog_fd = -1;
+	evsel->bperf_leader_link_fd = -1;
+
+	/*
+	 * Step 1: hold a fd on the leader program and the bpf_link, if
+	 * the program is not already gone, reload the program.
+	 * Use flock() to ensure exclusive access to the perf_event_attr
+	 * map.
+	 */
+	attr_map_fd = bperf_lock_attr_map(target);
+	if (attr_map_fd < 0) {
+		pr_err("Failed to lock perf_event_attr map\n");
+		return -1;
+	}
+
+	err = bpf_map_lookup_elem(attr_map_fd, &evsel->core.attr, &entry);
+	if (err) {
+		err = bpf_map_update_elem(attr_map_fd, &evsel->core.attr, &entry, BPF_ANY);
+		if (err)
+			goto out;
+	}
+
+	evsel->bperf_leader_link_fd = bpf_link_get_fd_by_id(entry.link_id);
+	if (evsel->bperf_leader_link_fd < 0 &&
+	    bperf_reload_leader_program(evsel, attr_map_fd, &entry)) {
+		err = -1;
+		goto out;
+	}
+	/*
+	 * The bpf_link holds reference to the leader program, and the
+	 * leader program holds reference to the maps. Therefore, if
+	 * link_id is valid, diff_map_id should also be valid.
+	 */
+	evsel->bperf_leader_prog_fd = bpf_prog_get_fd_by_id(
+		bpf_link_get_prog_id(evsel->bperf_leader_link_fd));
+	assert(evsel->bperf_leader_prog_fd >= 0);
+
+	diff_map_fd = bpf_map_get_fd_by_id(entry.diff_map_id);
+	assert(diff_map_fd >= 0);
+
+	/*
+	 * bperf uses BPF_PROG_TEST_RUN to get accurate reading. Check
+	 * whether the kernel support it
+	 */
+	err = bperf_trigger_reading(evsel->bperf_leader_prog_fd, 0);
+	if (err) {
+		pr_err("The kernel does not support test_run for raw_tp BPF programs.\n"
+		       "Therefore, --use-bpf might show inaccurate readings\n");
+		goto out;
+	}
+
+	/* Step 2: load the follower skeleton */
+	evsel->follower_skel = bperf_follower_bpf__open();
+	if (!evsel->follower_skel) {
+		err = -1;
+		pr_err("Failed to open follower skeleton\n");
+		goto out;
+	}
+
+	/* attach fexit program to the leader program */
+	bpf_program__set_attach_target(evsel->follower_skel->progs.fexit_XXX,
+				       evsel->bperf_leader_prog_fd, "on_switch");
+
+	/* connect to leader diff_reading map */
+	bpf_map__reuse_fd(evsel->follower_skel->maps.diff_readings, diff_map_fd);
+
+	/* set up reading map */
+	bpf_map__set_max_entries(evsel->follower_skel->maps.accum_readings,
+				 filter_entry_cnt);
+	/* set up follower filter based on target */
+	bpf_map__set_max_entries(evsel->follower_skel->maps.filter,
+				 filter_entry_cnt);
+	err = bperf_follower_bpf__load(evsel->follower_skel);
+	if (err) {
+		pr_err("Failed to load follower skeleton\n");
+		bperf_follower_bpf__destroy(evsel->follower_skel);
+		evsel->follower_skel = NULL;
+		goto out;
+	}
+
+	for (i = 0; i < filter_entry_cnt; i++) {
+		int filter_map_fd;
+		__u32 key;
+
+		if (filter_type == BPERF_FILTER_PID ||
+		    filter_type == BPERF_FILTER_TGID)
+			key = perf_thread_map__pid(evsel->core.threads, i);
+		else if (filter_type == BPERF_FILTER_CPU)
+			key = perf_cpu_map__cpu(evsel->core.cpus, i).cpu;
+		else
+			break;
+
+		filter_map_fd = bpf_map__fd(evsel->follower_skel->maps.filter);
+		bpf_map_update_elem(filter_map_fd, &key, &i, BPF_ANY);
+	}
+
+	evsel->follower_skel->bss->type = filter_type;
+
+	err = bperf_follower_bpf__attach(evsel->follower_skel);
+
+out:
+	if (err && evsel->bperf_leader_link_fd >= 0)
+		close(evsel->bperf_leader_link_fd);
+	if (err && evsel->bperf_leader_prog_fd >= 0)
+		close(evsel->bperf_leader_prog_fd);
+	if (diff_map_fd >= 0)
+		close(diff_map_fd);
+
+	flock(attr_map_fd, LOCK_UN);
+	close(attr_map_fd);
+
+	return err;
+}
+
+static int bperf__install_pe(struct evsel *evsel, int cpu_map_idx, int fd)
+{
+	struct bperf_leader_bpf *skel = evsel->leader_skel;
+
+	return bpf_map_update_elem(bpf_map__fd(skel->maps.events),
+				   &cpu_map_idx, &fd, BPF_ANY);
+}
+
+/*
+ * trigger the leader prog on each cpu, so the accum_reading map could get
+ * the latest readings.
+ */
+static int bperf_sync_counters(struct evsel *evsel)
+{
+	int num_cpu, i, cpu;
+
+	num_cpu = perf_cpu_map__nr(all_cpu_map);
+	for (i = 0; i < num_cpu; i++) {
+		cpu = perf_cpu_map__cpu(all_cpu_map, i).cpu;
+		bperf_trigger_reading(evsel->bperf_leader_prog_fd, cpu);
+	}
+	return 0;
+}
+
+static int bperf__enable(struct evsel *evsel)
+{
+	evsel->follower_skel->bss->enabled = 1;
+	return 0;
+}
+
+static int bperf__disable(struct evsel *evsel)
+{
+	evsel->follower_skel->bss->enabled = 0;
+	return 0;
+}
+
+static int bperf__read(struct evsel *evsel)
+{
+	struct bperf_follower_bpf *skel = evsel->follower_skel;
+	__u32 num_cpu_bpf = cpu__max_cpu().cpu;
+	struct bpf_perf_event_value values[num_cpu_bpf];
+	struct perf_counts_values *counts;
+	int reading_map_fd, err = 0;
+	__u32 i;
+	int j;
+
+	bperf_sync_counters(evsel);
+	reading_map_fd = bpf_map__fd(skel->maps.accum_readings);
+
+	for (i = 0; i < bpf_map__max_entries(skel->maps.accum_readings); i++) {
+		struct perf_cpu entry;
+		__u32 cpu;
+
+		err = bpf_map_lookup_elem(reading_map_fd, &i, values);
+		if (err)
+			goto out;
+		switch (evsel->follower_skel->bss->type) {
+		case BPERF_FILTER_GLOBAL:
+			assert(i == 0);
+
+			perf_cpu_map__for_each_cpu(entry, j, evsel__cpus(evsel)) {
+				counts = perf_counts(evsel->counts, j, 0);
+				counts->val = values[entry.cpu].counter;
+				counts->ena = values[entry.cpu].enabled;
+				counts->run = values[entry.cpu].running;
+			}
+			break;
+		case BPERF_FILTER_CPU:
+			cpu = perf_cpu_map__cpu(evsel__cpus(evsel), i).cpu;
+			assert(cpu >= 0);
+			counts = perf_counts(evsel->counts, i, 0);
+			counts->val = values[cpu].counter;
+			counts->ena = values[cpu].enabled;
+			counts->run = values[cpu].running;
+			break;
+		case BPERF_FILTER_PID:
+		case BPERF_FILTER_TGID:
+			counts = perf_counts(evsel->counts, 0, i);
+			counts->val = 0;
+			counts->ena = 0;
+			counts->run = 0;
+
+			for (cpu = 0; cpu < num_cpu_bpf; cpu++) {
+				counts->val += values[cpu].counter;
+				counts->ena += values[cpu].enabled;
+				counts->run += values[cpu].running;
+			}
+			break;
+		default:
+			break;
+		}
+	}
+out:
+	return err;
+}
+
+static int bperf__destroy(struct evsel *evsel)
+{
+	bperf_follower_bpf__destroy(evsel->follower_skel);
+	close(evsel->bperf_leader_prog_fd);
+	close(evsel->bperf_leader_link_fd);
+	return 0;
+}
+
+/*
+ * bperf: share hardware PMCs with BPF
+ *
+ * perf uses performance monitoring counters (PMC) to monitor system
+ * performance. The PMCs are limited hardware resources. For example,
+ * Intel CPUs have 3x fixed PMCs and 4x programmable PMCs per cpu.
+ *
+ * Modern data center systems use these PMCs in many different ways:
+ * system level monitoring, (maybe nested) container level monitoring, per
+ * process monitoring, profiling (in sample mode), etc. In some cases,
+ * there are more active perf_events than available hardware PMCs. To allow
+ * all perf_events to have a chance to run, it is necessary to do expensive
+ * time multiplexing of events.
+ *
+ * On the other hand, many monitoring tools count the common metrics
+ * (cycles, instructions). It is a waste to have multiple tools create
+ * multiple perf_events of "cycles" and occupy multiple PMCs.
+ *
+ * bperf tries to reduce such wastes by allowing multiple perf_events of
+ * "cycles" or "instructions" (at different scopes) to share PMUs. Instead
+ * of having each perf-stat session to read its own perf_events, bperf uses
+ * BPF programs to read the perf_events and aggregate readings to BPF maps.
+ * Then, the perf-stat session(s) reads the values from these BPF maps.
+ *
+ *                                ||
+ *       shared progs and maps <- || -> per session progs and maps
+ *                                ||
+ *   ---------------              ||
+ *   | perf_events |              ||
+ *   ---------------       fexit  ||      -----------------
+ *          |             --------||----> | follower prog |
+ *       --------------- /        || ---  -----------------
+ * cs -> | leader prog |/         ||/        |         |
+ *   --> ---------------         /||  --------------  ------------------
+ *  /       |         |         / ||  | filter map |  | accum_readings |
+ * /  ------------  ------------  ||  --------------  ------------------
+ * |  | prev map |  | diff map |  ||                        |
+ * |  ------------  ------------  ||                        |
+ *  \                             ||                        |
+ * = \ ==================================================== | ============
+ *    \                                                    /   user space
+ *     \                                                  /
+ *      \                                                /
+ *    BPF_PROG_TEST_RUN                    BPF_MAP_LOOKUP_ELEM
+ *        \                                            /
+ *         \                                          /
+ *          \------  perf-stat ----------------------/
+ *
+ * The figure above shows the architecture of bperf. Note that the figure
+ * is divided into 3 regions: shared progs and maps (top left), per session
+ * progs and maps (top right), and user space (bottom).
+ *
+ * The leader prog is triggered on each context switch (cs). The leader
+ * prog reads perf_events and stores the difference (current_reading -
+ * previous_reading) to the diff map. For the same metric, e.g. "cycles",
+ * multiple perf-stat sessions share the same leader prog.
+ *
+ * Each perf-stat session creates a follower prog as fexit program to the
+ * leader prog. It is possible to attach up to BPF_MAX_TRAMP_PROGS (38)
+ * follower progs to the same leader prog. The follower prog checks current
+ * task and processor ID to decide whether to add the value from the diff
+ * map to its accumulated reading map (accum_readings).
+ *
+ * Finally, perf-stat user space reads the value from accum_reading map.
+ *
+ * Besides context switch, it is also necessary to trigger the leader prog
+ * before perf-stat reads the value. Otherwise, the accum_reading map may
+ * not have the latest reading from the perf_events. This is achieved by
+ * triggering the event via sys_bpf(BPF_PROG_TEST_RUN) to each CPU.
+ *
+ * Comment before the definition of struct perf_event_attr_map_entry
+ * describes how different sessions of perf-stat share information about
+ * the leader prog.
+ */
+
+struct bpf_counter_ops bperf_ops = {
+	.load       = bperf__load,
+	.enable     = bperf__enable,
+	.disable    = bperf__disable,
+	.read       = bperf__read,
+	.install_pe = bperf__install_pe,
+	.destroy    = bperf__destroy,
+};
+
+extern struct bpf_counter_ops bperf_cgrp_ops;
+
+static inline bool bpf_counter_skip(struct evsel *evsel)
+{
+	return evsel->bpf_counter_ops == NULL;
+}
+
+int bpf_counter__install_pe(struct evsel *evsel, int cpu_map_idx, int fd)
+{
+	if (bpf_counter_skip(evsel))
+		return 0;
+	return evsel->bpf_counter_ops->install_pe(evsel, cpu_map_idx, fd);
+}
+
+int bpf_counter__load(struct evsel *evsel, struct target *target)
+{
+	if (target->bpf_str)
+		evsel->bpf_counter_ops = &bpf_program_profiler_ops;
+	else if (cgrp_event_expanded && target->use_bpf)
+		evsel->bpf_counter_ops = &bperf_cgrp_ops;
+	else if (target->use_bpf || evsel->bpf_counter ||
+		 evsel__match_bpf_counter_events(evsel->name))
+		evsel->bpf_counter_ops = &bperf_ops;
+
+	if (evsel->bpf_counter_ops)
+		return evsel->bpf_counter_ops->load(evsel, target);
+	return 0;
+}
+
+int bpf_counter__enable(struct evsel *evsel)
+{
+	if (bpf_counter_skip(evsel))
+		return 0;
+	return evsel->bpf_counter_ops->enable(evsel);
+}
+
+int bpf_counter__disable(struct evsel *evsel)
+{
+	if (bpf_counter_skip(evsel))
+		return 0;
+	return evsel->bpf_counter_ops->disable(evsel);
+}
+
+int bpf_counter__read(struct evsel *evsel)
+{
+	if (bpf_counter_skip(evsel))
+		return -EAGAIN;
+	return evsel->bpf_counter_ops->read(evsel);
+}
+
+void bpf_counter__destroy(struct evsel *evsel)
+{
+	if (bpf_counter_skip(evsel))
+		return;
+	evsel->bpf_counter_ops->destroy(evsel);
+	evsel->bpf_counter_ops = NULL;
+	evsel->bpf_skel = NULL;
+}