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From:   Riccardo Mancini <rickyman7@gmail.com>
To:     Arnaldo Carvalho de Melo <acme@kernel.org>
Cc:     Ian Rogers <irogers@google.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Jiri Olsa <jolsa@redhat.com>, linux-kernel@vger.kernel.org,
        linux-perf-users@vger.kernel.org,
        Riccardo Mancini <rickyman7@gmail.com>
Subject: [RFC PATCH v1 21/37] perf evsel: move ignore_missing_thread to fallback code
Date:   Sat, 21 Aug 2021 11:19:27 +0200
Message-Id: <4eca51443c786baaf6811b7cd8e73aafd97f7606.1629490974.git.rickyman7@gmail.com>
In-Reply-To: <cover.1629490974.git.rickyman7@gmail.com>
References: <cover.1629490974.git.rickyman7@gmail.com>
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This patch moves ignore_missing_thread outside the perf_event_open loop.
Doing so, we need to move the retry_open flag a few places higher, with
minimal impact. Furthermore, thread need not be decreased since it won't
get increased by the for loop (since we're jumping back inside), but we
need to check that the nthreads decrease didn't put thread out of range.

The goal is to have fallbacks handled in one place only, since in the
future parallel code, these would be handled separately.

Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
---
 tools/perf/util/evsel.c | 29 +++++++++++++----------------
 tools/perf/util/evsel.h |  5 +++++
 2 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 916930ea31450265..a1a88607fd59efcb 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1656,7 +1656,7 @@ static int update_fds(struct evsel *evsel,
 	return 0;
 }
 
-static bool ignore_missing_thread(struct evsel *evsel,
+bool evsel__ignore_missing_thread(struct evsel *evsel,
 				  int nr_cpus, int cpu,
 				  struct perf_thread_map *threads,
 				  int thread, int err)
@@ -1993,12 +1993,15 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
 
 		for (thread = 0; thread < nthreads; thread++) {
 			int fd, group_fd;
+retry_open:
+			if (thread >= nthreads)
+				break;
 
 			if (!evsel->cgrp && !evsel->core.system_wide)
 				pid = perf_thread_map__pid(threads, thread);
 
 			group_fd = get_group_fd(evsel, cpu, thread);
-retry_open:
+
 			test_attr__ready();
 
 			fd = perf_event_open(evsel, pid, cpus->map[cpu],
@@ -2016,20 +2019,6 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
 			if (fd < 0) {
 				err = -errno;
 
-				if (ignore_missing_thread(evsel, cpus->nr, cpu, threads, thread, err)) {
-					/*
-					 * We just removed 1 thread, so take a step
-					 * back on thread index and lower the upper
-					 * nthreads limit.
-					 */
-					nthreads--;
-					thread--;
-
-					/* ... and pretend like nothing have happened. */
-					err = 0;
-					continue;
-				}
-
 				pr_debug2_peo("\nsys_perf_event_open failed, error %d\n",
 					  err);
 				goto try_fallback;
@@ -2069,6 +2058,14 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
 	return 0;
 
 try_fallback:
+	if (evsel__ignore_missing_thread(evsel, cpus->nr, cpu, threads, thread, err)) {
+		/* We just removed 1 thread, so lower the upper nthreads limit. */
+		nthreads--;
+
+		/* ... and pretend like nothing have happened. */
+		err = 0;
+		goto retry_open;
+	}
 	/*
 	 * perf stat needs between 5 and 22 fds per CPU. When we run out
 	 * of them try to increase the limits.
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index bf9abd9a5cbf9852..661d2677a19b6248 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -293,6 +293,11 @@ bool evsel__detect_missing_features(struct evsel *evsel);
 enum rlimit_action { NO_CHANGE, SET_TO_MAX, INCREASED_MAX };
 bool evsel__increase_rlimit(enum rlimit_action *set_rlimit);
 
+bool evsel__ignore_missing_thread(struct evsel *evsel,
+				  int nr_cpus, int cpu,
+				  struct perf_thread_map *threads,
+				  int thread, int err);
+
 struct perf_sample;
 
 void *evsel__rawptr(struct evsel *evsel, struct perf_sample *sample, const char *name);
-- 
2.31.1