[PATCH v3] eal/unix: optimize thread creation with glibc

[David Marchand]

Setting the cpu affinity of the child thread from the parent thread is
racy when using pthread_setaffinity_np, as the child thread may start
running and initialize before affinity is set.

On the other hand, setting the cpu affinity from the child thread itself
may fail, so the parent thread waits for the child thread to report
whether this call succeeded.

This synchronisation point resulted in a significant slow down of
rte_thread_create() (as seen in the lcores_autotest unit tests, in OBS
for some ARM systems).

Another option for setting cpu affinity is to use the not portable
pthread_attr_setaffinity_np, but it is not available with musl.

Fixes: b28c6196b132 ("eal/unix: fix thread creation")
Cc: stable at dpdk.org

Signed-off-by: David Marchand <david.marchand at redhat.com>
Acked-by: Luca Boccassi <bluca at debian.org>
---
Changes since v2:
- added pthread_attr_setaffinity_np() detection,

Changes since v1:
- fixed build with FreeBSD,

---
 lib/eal/unix/meson.build  |  5 +++++
 lib/eal/unix/rte_thread.c | 25 +++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/lib/eal/unix/meson.build b/lib/eal/unix/meson.build
index cc7d67dd32..f845625a54 100644
--- a/lib/eal/unix/meson.build
+++ b/lib/eal/unix/meson.build
@@ -11,3 +11,8 @@ sources += files(
         'eal_unix_timer.c',
         'rte_thread.c',
 )
+
+if cc.has_function('pthread_attr_setaffinity_np', args: '-D_GNU_SOURCE',
+                   prefix : '#include <pthread.h>')
+    cflags += '-DRTE_EAL_PTHREAD_ATTR_SETAFFINITY_NP'
+endif
diff --git a/lib/eal/unix/rte_thread.c b/lib/eal/unix/rte_thread.c
index 1b4c73f58e..ea629c2065 100644
--- a/lib/eal/unix/rte_thread.c
+++ b/lib/eal/unix/rte_thread.c
@@ -19,6 +19,7 @@ struct eal_tls_key {
 	pthread_key_t thread_index;
 };
 
+#ifndef RTE_EAL_PTHREAD_ATTR_SETAFFINITY_NP
 struct thread_start_context {
 	rte_thread_func thread_func;
 	void *thread_args;
@@ -28,6 +29,7 @@ struct thread_start_context {
 	int wrapper_ret;
 	bool wrapper_done;
 };
+#endif
 
 static int
 thread_map_priority_to_os_value(enum rte_thread_priority eal_pri, int *os_pri,
@@ -88,6 +90,7 @@ thread_map_os_priority_to_eal_priority(int policy, int os_pri,
 	return 0;
 }
 
+#ifndef RTE_EAL_PTHREAD_ATTR_SETAFFINITY_NP
 static void *
 thread_start_wrapper(void *arg)
 {
@@ -113,6 +116,7 @@ thread_start_wrapper(void *arg)
 
 	return (void *)(uintptr_t)thread_func(thread_args);
 }
+#endif
 
 int
 rte_thread_create(rte_thread_t *thread_id,
@@ -126,6 +130,7 @@ rte_thread_create(rte_thread_t *thread_id,
 		.sched_priority = 0,
 	};
 	int policy = SCHED_OTHER;
+#ifndef RTE_EAL_PTHREAD_ATTR_SETAFFINITY_NP
 	struct thread_start_context ctx = {
 		.thread_func = thread_func,
 		.thread_args = args,
@@ -134,6 +139,7 @@ rte_thread_create(rte_thread_t *thread_id,
 		.wrapper_mutex = PTHREAD_MUTEX_INITIALIZER,
 		.wrapper_cond = PTHREAD_COND_INITIALIZER,
 	};
+#endif
 
 	if (thread_attr != NULL) {
 		ret = pthread_attr_init(&attr);
@@ -144,6 +150,16 @@ rte_thread_create(rte_thread_t *thread_id,
 
 		attrp = &attr;
 
+#ifdef RTE_EAL_PTHREAD_ATTR_SETAFFINITY_NP
+		if (CPU_COUNT(&thread_attr->cpuset) > 0) {
+			ret = pthread_attr_setaffinity_np(attrp, sizeof(thread_attr->cpuset),
+				&thread_attr->cpuset);
+			if (ret != 0) {
+				EAL_LOG(DEBUG, "pthread_attr_setaffinity_np failed");
+				goto cleanup;
+			}
+		}
+#endif
 		/*
 		 * Set the inherit scheduler parameter to explicit,
 		 * otherwise the priority attribute is ignored.
@@ -178,6 +194,14 @@ rte_thread_create(rte_thread_t *thread_id,
 		}
 	}
 
+#ifdef RTE_EAL_PTHREAD_ATTR_SETAFFINITY_NP
+	ret = pthread_create((pthread_t *)&thread_id->opaque_id, attrp,
+		(void *)(void *)thread_func, args);
+	if (ret != 0) {
+		EAL_LOG(DEBUG, "pthread_create failed");
+		goto cleanup;
+	}
+#else /* !RTE_EAL_PTHREAD_ATTR_SETAFFINITY_NP */
 	ret = pthread_create((pthread_t *)&thread_id->opaque_id, attrp,
 		thread_start_wrapper, &ctx);
 	if (ret != 0) {
@@ -193,6 +217,7 @@ rte_thread_create(rte_thread_t *thread_id,
 
 	if (ret != 0)
 		rte_thread_join(*thread_id, NULL);
+#endif /* RTE_EAL_PTHREAD_ATTR_SETAFFINITY_NP */
 
 cleanup:
 	if (attrp != NULL)
-- 
2.46.2