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

[David Marchand <david.marchand@redhat.com>]

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.
Assume availability by relying on __USE_GNU that is not set with musl.

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

Signed-off-by: David Marchand <david.marchand@redhat.com>
---
 lib/eal/unix/rte_thread.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/lib/eal/unix/rte_thread.c b/lib/eal/unix/rte_thread.c
index 1b4c73f58e..e42b6c37a2 100644
--- a/lib/eal/unix/rte_thread.c
+++ b/lib/eal/unix/rte_thread.c
@@ -4,6 +4,7 @@
  */
 
 #include <errno.h>
+#include <features.h>
 #include <pthread.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -19,6 +20,7 @@ struct eal_tls_key {
 	pthread_key_t thread_index;
 };
 
+#ifndef __USE_GNU
 struct thread_start_context {
 	rte_thread_func thread_func;
 	void *thread_args;
@@ -28,6 +30,7 @@ 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 +91,7 @@ thread_map_os_priority_to_eal_priority(int policy, int os_pri,
 	return 0;
 }
 
+#ifndef __USE_GNU
 static void *
 thread_start_wrapper(void *arg)
 {
@@ -113,6 +117,7 @@ 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 +131,7 @@ rte_thread_create(rte_thread_t *thread_id,
 		.sched_priority = 0,
 	};
 	int policy = SCHED_OTHER;
+#ifndef __USE_GNU
 	struct thread_start_context ctx = {
 		.thread_func = thread_func,
 		.thread_args = args,
@@ -134,6 +140,7 @@ 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 +151,16 @@ rte_thread_create(rte_thread_t *thread_id,
 
 		attrp = &attr;
 
+#ifdef __USE_GNU
+		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 +195,14 @@ rte_thread_create(rte_thread_t *thread_id,
 		}
 	}
 
+#ifdef __USE_GNU
+	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 /* !__USE_GNU */
 	ret = pthread_create((pthread_t *)&thread_id->opaque_id, attrp,
 		thread_start_wrapper, &ctx);
 	if (ret != 0) {
@@ -193,6 +218,7 @@ rte_thread_create(rte_thread_t *thread_id,
 
 	if (ret != 0)
 		rte_thread_join(*thread_id, NULL);
+#endif /* __USE_GNU */
 
 cleanup:
 	if (attrp != NULL)
-- 
2.46.2