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, 68 insertions, 14 deletions

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 8cc24967bc27..3c054b8d4677 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -67,6 +67,7 @@
 #include "util/top.h"
 #include "util/affinity.h"
 #include "util/pfm.h"
+#include "util/bpf_counter.h"
 #include "asm/bug.h"
 
 #include <linux/time64.h>
@@ -409,12 +410,32 @@ static int read_affinity_counters(struct timespec *rs)
 	return 0;
 }
 
+static int read_bpf_map_counters(void)
+{
+	struct evsel *counter;
+	int err;
+
+	evlist__for_each_entry(evsel_list, counter) {
+		err = bpf_counter__read(counter);
+		if (err)
+			return err;
+	}
+	return 0;
+}
+
 static void read_counters(struct timespec *rs)
 {
 	struct evsel *counter;
+	int err;
 
-	if (!stat_config.stop_read_counter && (read_affinity_counters(rs) < 0))
-		return;
+	if (!stat_config.stop_read_counter) {
+		if (target__has_bpf(&target))
+			err = read_bpf_map_counters();
+		else
+			err = read_affinity_counters(rs);
+		if (err < 0)
+			return;
+	}
 
 	evlist__for_each_entry(evsel_list, counter) {
 		if (counter->err)
@@ -496,11 +517,22 @@ static bool handle_interval(unsigned int interval, int *times)
 	return false;
 }
 
-static void enable_counters(void)
+static int enable_counters(void)
 {
+	struct evsel *evsel;
+	int err;
+
+	if (target__has_bpf(&target)) {
+		evlist__for_each_entry(evsel_list, evsel) {
+			err = bpf_counter__enable(evsel);
+			if (err)
+				return err;
+		}
+	}
+
 	if (stat_config.initial_delay < 0) {
 		pr_info(EVLIST_DISABLED_MSG);
-		return;
+		return 0;
 	}
 
 	if (stat_config.initial_delay > 0) {
@@ -518,6 +550,7 @@ static void enable_counters(void)
 		if (stat_config.initial_delay > 0)
 			pr_info(EVLIST_ENABLED_MSG);
 	}
+	return 0;
 }
 
 static void disable_counters(void)
@@ -720,7 +753,7 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
 	const bool forks = (argc > 0);
 	bool is_pipe = STAT_RECORD ? perf_stat.data.is_pipe : false;
 	struct affinity affinity;
-	int i, cpu;
+	int i, cpu, err;
 	bool second_pass = false;
 
 	if (forks) {
@@ -737,6 +770,13 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
 	if (affinity__setup(&affinity) < 0)
 		return -1;
 
+	if (target__has_bpf(&target)) {
+		evlist__for_each_entry(evsel_list, counter) {
+			if (bpf_counter__load(counter, &target))
+				return -1;
+		}
+	}
+
 	evlist__for_each_cpu (evsel_list, i, cpu) {
 		affinity__set(&affinity, cpu);
 
@@ -850,7 +890,7 @@ try_again_reset:
 	}
 
 	if (STAT_RECORD) {
-		int err, fd = perf_data__fd(&perf_stat.data);
+		int fd = perf_data__fd(&perf_stat.data);
 
 		if (is_pipe) {
 			err = perf_header__write_pipe(perf_data__fd(&perf_stat.data));
@@ -876,7 +916,9 @@ try_again_reset:
 
 	if (forks) {
 		evlist__start_workload(evsel_list);
-		enable_counters();
+		err = enable_counters();
+		if (err)
+			return -1;
 
 		if (interval || timeout || evlist__ctlfd_initialized(evsel_list))
 			status = dispatch_events(forks, timeout, interval, &times);
@@ -895,7 +937,9 @@ try_again_reset:
 		if (WIFSIGNALED(status))
 			psignal(WTERMSIG(status), argv[0]);
 	} else {
-		enable_counters();
+		err = enable_counters();
+		if (err)
+			return -1;
 		status = dispatch_events(forks, timeout, interval, &times);
 	}
 
@@ -1085,6 +1129,10 @@ static struct option stat_options[] = {
 		   "stat events on existing process id"),
 	OPT_STRING('t', "tid", &target.tid, "tid",
 		   "stat events on existing thread id"),
+#ifdef HAVE_BPF_SKEL
+	OPT_STRING('b', "bpf-prog", &target.bpf_str, "bpf-prog-id",
+		   "stat events on existing bpf program id"),
+#endif
 	OPT_BOOLEAN('a', "all-cpus", &target.system_wide,
 		    "system-wide collection from all CPUs"),
 	OPT_BOOLEAN('g', "group", &group,
@@ -2064,11 +2112,12 @@ int cmd_stat(int argc, const char **argv)
 		"perf stat [<options>] [<command>]",
 		NULL
 	};
-	int status = -EINVAL, run_idx;
+	int status = -EINVAL, run_idx, err;
 	const char *mode;
 	FILE *output = stderr;
 	unsigned int interval, timeout;
 	const char * const stat_subcommands[] = { "record", "report" };
+	char errbuf[BUFSIZ];
 
 	setlocale(LC_ALL, "");
 
@@ -2179,6 +2228,12 @@ int cmd_stat(int argc, const char **argv)
 	} else if (big_num_opt == 0) /* User passed --no-big-num */
 		stat_config.big_num = false;
 
+	err = target__validate(&target);
+	if (err) {
+		target__strerror(&target, err, errbuf, BUFSIZ);
+		pr_warning("%s\n", errbuf);
+	}
+
 	setup_system_wide(argc);
 
 	/*
@@ -2252,8 +2307,6 @@ int cmd_stat(int argc, const char **argv)
 		}
 	}
 
-	target__validate(&target);
-
 	if ((stat_config.aggr_mode == AGGR_THREAD) && (target.system_wide))
 		target.per_thread = true;
 
@@ -2384,9 +2437,10 @@ int cmd_stat(int argc, const char **argv)
 		 * tools remain  -acme
 		 */
 		int fd = perf_data__fd(&perf_stat.data);
-		int err = perf_event__synthesize_kernel_mmap((void *)&perf_stat,
-							     process_synthesized_event,
-							     &perf_stat.session->machines.host);
+
+		err = perf_event__synthesize_kernel_mmap((void *)&perf_stat,
+							 process_synthesized_event,
+							 &perf_stat.session->machines.host);
 		if (err) {
 			pr_warning("Couldn't synthesize the kernel mmap record, harmless, "
 				   "older tools may produce warnings about this file\n.");