MINOR: thread: implement ha_thread_relax()

At some places we're using a painful ifdef to decide whether to use
sched_yield() or pl_cpu_relax() to relax in loops, this is hardly
exportable. Let's move this to ha_thread_relax() instead and une
this one only.

include/common/hathreads.h

@@ -22,6 +22,11 @@
 #ifndef _COMMON_HATHREADS_H
 #define _COMMON_HATHREADS_H
 
+#include <unistd.h>
+#ifdef _POSIX_PRIORITY_SCHEDULING
+#include <sched.h>
+#endif
+
 #include <common/config.h>
 #include <common/initcall.h>
 
@@ -130,6 +135,13 @@ static inline void ha_set_tid(unsigned int tid)
 {
 }
 
+static inline void ha_thread_relax(void)
+{
+#if _POSIX_PRIORITY_SCHEDULING
+	sched_yield();
+#endif
+}
+
 static inline void __ha_barrier_atomic_load(void)
 {
 }
@@ -391,6 +403,15 @@ static inline void ha_set_tid(unsigned int data)
 	tid_bit = (1UL << tid);
 }
 
+static inline void ha_thread_relax(void)
+{
+#if _POSIX_PRIORITY_SCHEDULING
+	sched_yield();
+#else
+	pl_cpu_relax();
+#endif
+}
+
 /* Marks the thread as harmless. Note: this must be true, i.e. the thread must
  * not be touching any unprotected shared resource during this period. Usually
  * this is called before poll(), but it may also be placed around very slow

src/hathreads.c

@@ -52,11 +52,7 @@ void thread_harmless_till_end()
 {
 		_HA_ATOMIC_OR(&threads_harmless_mask, tid_bit);
 		while (threads_want_rdv_mask & all_threads_mask) {
-#if _POSIX_PRIORITY_SCHEDULING
-			sched_yield();
-#else
-			pl_cpu_relax();
-#endif
+			ha_thread_relax();
 		}
 }
 
@@ -81,11 +77,7 @@ void thread_isolate()
 		else if (_HA_ATOMIC_CAS(&threads_harmless_mask, &old, old & ~tid_bit))
 			break;
 
-#if _POSIX_PRIORITY_SCHEDULING
-		sched_yield();
-#else
-		pl_cpu_relax();
-#endif
+		ha_thread_relax();
 	}
 	/* one thread gets released at a time here, with its harmess bit off.
 	 * The loss of this bit makes the other one continue to spin while the