linux-kernel - [PATCH] perf bench futex, wake: Fixlets for futex

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Date:   Mon, 11 Oct 2021 20:09:14 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     acme@...nel.org
Cc:     linux-kernel@...r.kernel.org, dave@...olabs.net,
        Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH] perf bench futex, wake: Fixlets for futex_wait return checks

- Avoid checking against EINTR which has for a very long time no longer
been the case for spurious wakeups. Properly use EAGAIN instead - albeit
there should be no error scenarios in these workloads.

- Do not bogusly check syscall(2) return, but instead rely on errno.

- Use warn() instead of warnx() for we want an appended message.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 tools/perf/bench/futex-requeue.c       |  4 ++--
 tools/perf/bench/futex-wake-parallel.c | 13 +++++++++++--
 tools/perf/bench/futex-wake.c          | 11 ++++++++++-
 3 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/tools/perf/bench/futex-requeue.c b/tools/perf/bench/futex-requeue.c
index 97fe31fd3a23..ef09ca189e47 100644
--- a/tools/perf/bench/futex-requeue.c
+++ b/tools/perf/bench/futex-requeue.c
@@ -97,7 +97,7 @@ static void *workerfn(void *arg __maybe_unused)
 
 			if (ret && errno != EAGAIN) {
 				if (!params.silent)
-					warnx("futex_wait");
+					warn("futex_wait");
 				break;
 			}
 		} else {
@@ -111,7 +111,7 @@ static void *workerfn(void *arg __maybe_unused)
 
 			if (ret && errno != EAGAIN) {
 				if (!params.silent)
-					warnx("futex_wait_requeue_pi");
+					warn("futex_wait_requeue_pi");
 				break;
 			}
 		}
diff --git a/tools/perf/bench/futex-wake-parallel.c b/tools/perf/bench/futex-wake-parallel.c
index e970e6b9ad53..76b57eac2375 100644
--- a/tools/perf/bench/futex-wake-parallel.c
+++ b/tools/perf/bench/futex-wake-parallel.c
@@ -132,9 +132,18 @@ static void *blocked_workerfn(void *arg __maybe_unused)
 	pthread_cond_wait(&thread_worker, &thread_lock);
 	pthread_mutex_unlock(&thread_lock);
 
-	while (1) { /* handle spurious wakeups */
-		if (futex_wait(&futex, 0, NULL, futex_flag) != EINTR)
+	while (1) {
+		int ret;
+
+		ret = futex_wait(&futex, 0, NULL, futex_flag);
+		if (!ret)
+			break;
+
+		if (ret && errno != EAGAIN) {
+			if (!params.silent)
+				warn("futex_wait");
 			break;
+		}
 	}
 
 	pthread_exit(NULL);
diff --git a/tools/perf/bench/futex-wake.c b/tools/perf/bench/futex-wake.c
index 77f058a47790..8e99b506d4f0 100644
--- a/tools/perf/bench/futex-wake.c
+++ b/tools/perf/bench/futex-wake.c
@@ -73,8 +73,17 @@ static void *workerfn(void *arg __maybe_unused)
 	pthread_mutex_unlock(&thread_lock);
 
 	while (1) {
-		if (futex_wait(&futex1, 0, NULL, futex_flag) != EINTR)
+		int ret;
+
+		ret = futex_wait(&futex1, 0, NULL, futex_flag);
+		if (!ret)
+			break;
+
+		if (ret && errno != EAGAIN) {
+			if (!params.silent)
+				warn("futex_wait");
 			break;
+		}
 	}
 
 	pthread_exit(NULL);
-- 
2.26.2