Caching scheduling policy and priority in userland, a critical but baddly

written application is frequently changing thread priority for SCHED_OTHER
policy.

5 files changed, 50 insertions, 20 deletions

diff --git a/lib/libthr/thread/thr_create.c b/lib/libthr/thread/thr_create.c
index 49e9b45..f0d7cd5 100644
--- a/lib/libthr/thread/thr_create.c
+++ b/lib/libthr/thread/thr_create.c
@@ -79,10 +79,9 @@ _pthread_create(pthread_t * thread, const pthread_attr_t * attr,
 			new_thread->attr.flags |= PTHREAD_SCOPE_SYSTEM;
 		else
 			new_thread->attr.flags &= ~PTHREAD_SCOPE_SYSTEM;
-		/*
-		 * scheduling policy and scheduling parameters will be
-		 * inherited in following code.
-		 */
+
+		new_thread->attr.prio = curthread->attr.prio;
+		new_thread->attr.sched_policy = curthread->attr.sched_policy;
 	}
 
 	if (_thr_scope_system > 0)
diff --git a/lib/libthr/thread/thr_getschedparam.c b/lib/libthr/thread/thr_getschedparam.c
index 9d581ed..c3233cd 100644
--- a/lib/libthr/thread/thr_getschedparam.c
+++ b/lib/libthr/thread/thr_getschedparam.c
@@ -57,20 +57,17 @@ _pthread_getschedparam(pthread_t pthread, int *policy,
 		 * thread.
 		 */
 		THR_LOCK(curthread);
-		ret = thr_getscheduler((pid_t)curthread->tid, policy, param,
-			sizeof(param));
-		if (ret == -1)
-			ret = errno;
+		*policy = curthread->attr.sched_policy;
+		param->sched_priority = curthread->attr.prio;
 		THR_UNLOCK(curthread);
+		ret = 0;
 	}
 	/* Find the thread in the list of active threads. */
 	else if ((ret = _thr_ref_add(curthread, pthread, /*include dead*/0))
 	    == 0) {
 		THR_THREAD_LOCK(curthread, pthread);
-		ret = thr_getscheduler(pthread->tid, policy, param,
-			sizeof(param));
-		if (ret == -1)
-			ret = errno;
+		*policy = pthread->attr.sched_policy;
+		param->sched_priority = pthread->attr.prio;
 		THR_THREAD_UNLOCK(curthread, pthread);
 		_thr_ref_delete(curthread, pthread);
 	}
diff --git a/lib/libthr/thread/thr_init.c b/lib/libthr/thread/thr_init.c
index 99bcea3..490c1b7 100644
--- a/lib/libthr/thread/thr_init.c
+++ b/lib/libthr/thread/thr_init.c
@@ -362,6 +362,8 @@ _libpthread_init(struct pthread *curthread)
 static void
 init_main_thread(struct pthread *thread)
 {
+	struct sched_param sched_param;
+
 	/* Setup the thread attributes. */
 	thr_self(&thread->tid);
 	thread->attr = _pthread_attr_default;
@@ -407,6 +409,10 @@ init_main_thread(struct pthread *thread)
 
 	thread->state = PS_RUNNING;
 
+	thr_getscheduler(thread->tid, &thread->attr.sched_policy,
+		 &sched_param, sizeof(sched_param));
+	thread->attr.prio = sched_param.sched_priority;
+
 	/* Others cleared to zero by thr_alloc() */
 }
 
diff --git a/lib/libthr/thread/thr_setprio.c b/lib/libthr/thread/thr_setprio.c
index 03ac39c..78769d1 100644
--- a/lib/libthr/thread/thr_setprio.c
+++ b/lib/libthr/thread/thr_setprio.c
@@ -50,20 +50,34 @@ _pthread_setprio(pthread_t pthread, int prio)
 	param.sched_priority = prio;
 	if (pthread == curthread) {
 		THR_LOCK(curthread);
-		ret = thr_setschedparam(curthread->tid, &param, sizeof(param));
-		if (ret == -1)
-			ret = errno;
-		else
+		if (curthread->attr.sched_policy == SCHED_OTHER ||
+		    curthread->attr.prio == prio) {
 			curthread->attr.prio = prio;
+			ret = 0;
+		} else {
+			ret = thr_setschedparam(curthread->tid,
+				 &param, sizeof(param));
+			if (ret == -1)
+				ret = errno;
+			else 
+				curthread->attr.prio = prio;
+		}
 		THR_UNLOCK(curthread);
 	} else if ((ret = _thr_ref_add(curthread, pthread, /*include dead*/0))
 		== 0) {
 		THR_THREAD_LOCK(curthread, pthread);
-		ret = thr_setschedparam(pthread->tid, &param, sizeof(param));
-		if (ret == -1)
-			ret = errno;
-		else
+		if (pthread->attr.sched_policy == SCHED_OTHER ||
+		    pthread->attr.prio == prio) {
 			pthread->attr.prio = prio;
+			ret = 0;
+		} else {
+			ret = thr_setschedparam(pthread->tid, &param,
+				sizeof(param));
+			if (ret == -1)
+				ret = errno;
+			else
+				pthread->attr.prio = prio;
+		}
 		THR_THREAD_UNLOCK(curthread, pthread);
 		_thr_ref_delete(curthread, pthread);
 	}
diff --git a/lib/libthr/thread/thr_setschedparam.c b/lib/libthr/thread/thr_setschedparam.c
index 5e2d2bf..d766e37 100644
--- a/lib/libthr/thread/thr_setschedparam.c
+++ b/lib/libthr/thread/thr_setschedparam.c
@@ -55,6 +55,13 @@ _pthread_setschedparam(pthread_t pthread, int policy,
 
 	if (pthread == curthread) {
 		THR_LOCK(curthread);
+		if (curthread->attr.sched_policy == policy &&
+		    (policy == SCHED_OTHER ||
+		     curthread->attr.prio == param->sched_priority)) {
+			pthread->attr.prio = param->sched_priority;
+			THR_UNLOCK(curthread);
+			return (0);
+		}
 		ret = thr_setscheduler(curthread->tid, policy, param,
 			sizeof(param));
 		if (ret == -1)
@@ -67,6 +74,13 @@ _pthread_setschedparam(pthread_t pthread, int policy,
 	} else if ((ret = _thr_ref_add(curthread, pthread, /*include dead*/0))
 		== 0) {
 		THR_THREAD_LOCK(curthread, pthread);
+		if (pthread->attr.sched_policy == policy &&
+		    (policy == SCHED_OTHER ||
+		     pthread->attr.prio == param->sched_priority)) {
+			pthread->attr.prio = param->sched_priority;
+			THR_THREAD_UNLOCK(curthread, pthread);
+			return (0);
+		}
 		ret = thr_setscheduler(pthread->tid, policy, param,
 			sizeof(param));
 		if (ret == -1)