linux-kernel - [RFC PATCH v1 24/37] perf evsel: handle precise_ip fallback in evsel__open

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Date:   Sat, 21 Aug 2021 11:19:30 +0200
From:   Riccardo Mancini <rickyman7@...il.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Ian Rogers <irogers@...gle.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Riccardo Mancini <rickyman7@...il.com>
Subject: [RFC PATCH v1 24/37] perf evsel: handle precise_ip fallback in evsel__open_cpu

This is another patch in the effort to separate the fallback mechanisms
from the open itself.

In case of precise_ip fallback, the original precise_ip will be stored
in the evsel (it was stored in a local variable) and the open will be
retried. Since the precise_ip fallback will be the first in the chain of
fallbacks, there should be no functional change with this patch.

Signed-off-by: Riccardo Mancini <rickyman7@...il.com>
---
 tools/perf/util/evsel.c | 59 ++++++++++++++++++-----------------------
 tools/perf/util/evsel.h |  2 ++
 2 files changed, 28 insertions(+), 33 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 3e556afed8dd396c..2e95416b8320c6b9 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1709,42 +1709,29 @@ static void display_attr(struct perf_event_attr *attr)
 	}
 }
 
-static int perf_event_open(struct evsel *evsel,
-			   pid_t pid, int cpu, int group_fd)
+bool evsel__precise_ip_fallback(struct evsel *evsel)
 {
-	int precise_ip = evsel->core.attr.precise_ip;
-	int fd;
-
-	while (1) {
-		pr_debug2_peo("sys_perf_event_open: pid %d  cpu %d  group_fd %d  flags %#lx",
-			  pid, cpu, group_fd, evsel->open_flags);
-
-		fd = sys_perf_event_open(&evsel->core.attr, pid, cpu, group_fd, evsel->open_flags);
-		if (fd >= 0)
-			break;
-
-		/* Do not try less precise if not requested. */
-		if (!evsel->precise_max)
-			break;
-
-		/*
-		 * We tried all the precise_ip values, and it's
-		 * still failing, so leave it to standard fallback.
-		 */
-		if (!evsel->core.attr.precise_ip) {
-			evsel->core.attr.precise_ip = precise_ip;
-			break;
-		}
+	/* Do not try less precise if not requested. */
+	if (!evsel->precise_max)
+		return false;
 
-		pr_debug2_peo("\nsys_perf_event_open failed, error %d\n", -ENOTSUP);
-		evsel->core.attr.precise_ip--;
-		pr_debug2_peo("decreasing precise_ip by one (%d)\n", evsel->core.attr.precise_ip);
-		display_attr(&evsel->core.attr);
+	/*
+	 * We tried all the precise_ip values, and it's
+	 * still failing, so leave it to standard fallback.
+	 */
+	if (!evsel->core.attr.precise_ip) {
+		evsel->core.attr.precise_ip = evsel->precise_ip_original;
+		return false;
 	}
 
-	return fd;
-}
+	if (!evsel->precise_ip_original)
+		evsel->precise_ip_original = evsel->core.attr.precise_ip;
 
+	evsel->core.attr.precise_ip--;
+	pr_debug2_peo("decreasing precise_ip by one (%d)\n", evsel->core.attr.precise_ip);
+	display_attr(&evsel->core.attr);
+	return true;
+}
 
 static struct perf_cpu_map *empty_cpu_map;
 static struct perf_thread_map *empty_thread_map;
@@ -2004,8 +1991,11 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
 
 			test_attr__ready();
 
-			fd = perf_event_open(evsel, pid, cpus->map[cpu],
-					     group_fd);
+			pr_debug2_peo("sys_perf_event_open: pid %d  cpu %d  group_fd %d  flags %#lx",
+				pid, cpus->map[cpu], group_fd, evsel->open_flags);
+
+			fd = sys_perf_event_open(&evsel->core.attr, pid, cpus->map[cpu],
+						group_fd, evsel->open_flags);
 
 			FD(evsel, cpu, thread) = fd;
 
@@ -2058,6 +2048,9 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
 	return 0;
 
 try_fallback:
+	if (evsel__precise_ip_fallback(evsel))
+		goto retry_open;
+
 	if (evsel__ignore_missing_thread(evsel, cpus->nr, cpu, threads, thread, err)) {
 		/* We just removed 1 thread, so lower the upper nthreads limit. */
 		nthreads--;
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 661d2677a19b6248..0a245afab2d87d74 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -150,6 +150,7 @@ struct evsel {
 		struct bperf_follower_bpf *follower_skel;
 	};
 	unsigned long		open_flags;
+	int			precise_ip_original;
 };
 
 struct perf_missing_features {
@@ -297,6 +298,7 @@ bool evsel__ignore_missing_thread(struct evsel *evsel,
 				  int nr_cpus, int cpu,
 				  struct perf_thread_map *threads,
 				  int thread, int err);
+bool evsel__precise_ip_fallback(struct evsel *evsel);
 
 struct perf_sample;
 
-- 
2.31.1