From 692cd1a3b2610d446b7cdbbb8990b3004eba6c2c Mon Sep 17 00:00:00 2001
From: "Pedro F. Giffuni" <pfg@FreeBSD.org>
Date: Mon, 23 Jan 2017 15:39:51 +0000
Subject: sort - Don't live-loop threads.

Worker threads now use a pthread_cond_t to wait for work instead of
burning the cpu up.

Obtained from:	DragonflyBSD (07774aea0ccf64a48fcfad8899e3bf7c8f18277a)
MFC after:	2 weeks
---
 usr.bin/sort/radixsort.c | 52 ++++++++++++++++++++++++++----------------------
 1 file changed, 28 insertions(+), 24 deletions(-)

(limited to 'usr.bin')

diff --git a/usr.bin/sort/radixsort.c b/usr.bin/sort/radixsort.c
index 79f4346eb3ec..62b946063f0f 100644
--- a/usr.bin/sort/radixsort.c
+++ b/usr.bin/sort/radixsort.c
@@ -83,12 +83,12 @@ static struct level_stack *g_ls;
 
 #if defined(SORT_THREADS)
 /* stack guarding mutex */
+static pthread_cond_t g_ls_cond;
 static pthread_mutex_t g_ls_mutex;
 
 /* counter: how many items are left */
 static size_t sort_left;
 /* guarding mutex */
-static pthread_mutex_t sort_left_mutex;
 
 /* semaphore to count threads */
 static sem_t mtsem;
@@ -99,23 +99,25 @@ static sem_t mtsem;
 static inline void
 sort_left_dec(size_t n)
 {
-
-	pthread_mutex_lock(&sort_left_mutex);
+	pthread_mutex_lock(&g_ls_mutex);
 	sort_left -= n;
-	pthread_mutex_unlock(&sort_left_mutex);
+	if (sort_left == 0 && nthreads > 1)
+		pthread_cond_broadcast(&g_ls_cond);
+	pthread_mutex_unlock(&g_ls_mutex);
 }
 
 /*
  * Do we have something to sort ?
+ *
+ * This routine does not need to be locked.
  */
 static inline bool
 have_sort_left(void)
 {
 	bool ret;
 
-	pthread_mutex_lock(&sort_left_mutex);
 	ret = (sort_left > 0);
-	pthread_mutex_unlock(&sort_left_mutex);
+
 	return (ret);
 }
 
@@ -144,6 +146,11 @@ push_ls(struct sort_level *sl)
 	new_ls->next = g_ls;
 	g_ls = new_ls;
 
+#if defined(SORT_THREADS)
+	if (nthreads > 1)
+		pthread_cond_signal(&g_ls_cond);
+#endif
+
 #if defined(SORT_THREADS)
 	if (nthreads > 1)
 		pthread_mutex_unlock(&g_ls_mutex);
@@ -184,13 +191,19 @@ pop_ls_mt(void)
 
 	pthread_mutex_lock(&g_ls_mutex);
 
-	if (g_ls) {
-		sl = g_ls->sl;
-		saved_ls = g_ls;
-		g_ls = g_ls->next;
-	} else {
+	for (;;) {
+		if (g_ls) {
+			sl = g_ls->sl;
+			saved_ls = g_ls;
+			g_ls = g_ls->next;
+			break;
+		}
 		sl = NULL;
 		saved_ls = NULL;
+
+		if (have_sort_left() == 0)
+			break;
+		pthread_cond_wait(&g_ls_cond, &g_ls_mutex);
 	}
 
 	pthread_mutex_unlock(&g_ls_mutex);
@@ -495,13 +508,8 @@ run_sort_cycle_mt(void)
 
 	for (;;) {
 		slc = pop_ls_mt();
-		if (slc == NULL) {
-			if (have_sort_left()) {
-				pthread_yield();
-				continue;
-			}
+		if (slc == NULL)
 			break;
-		}
 		run_sort_level_next(slc);
 	}
 }
@@ -512,9 +520,7 @@ run_sort_cycle_mt(void)
 static void*
 sort_thread(void* arg)
 {
-
 	run_sort_cycle_mt();
-
 	sem_post(&mtsem);
 
 	return (arg);
@@ -610,8 +616,7 @@ run_top_sort_level(struct sort_level *sl)
 			pthread_t pth;
 
 			pthread_attr_init(&attr);
-			pthread_attr_setdetachstate(&attr,
-			    PTHREAD_DETACHED);
+			pthread_attr_setdetachstate(&attr, PTHREAD_DETACHED);
 
 			for (;;) {
 				int res = pthread_create(&pth, &attr,
@@ -628,7 +633,7 @@ run_top_sort_level(struct sort_level *sl)
 			pthread_attr_destroy(&attr);
 		}
 
-		for(i = 0; i < nthreads; ++i)
+		for (i = 0; i < nthreads; ++i)
 			sem_wait(&mtsem);
 	}
 #endif /* defined(SORT_THREADS) */
@@ -651,7 +656,7 @@ run_sort(struct sort_list_item **base, size_t nmemb)
 		pthread_mutexattr_settype(&mattr, PTHREAD_MUTEX_ADAPTIVE_NP);
 
 		pthread_mutex_init(&g_ls_mutex, &mattr);
-		pthread_mutex_init(&sort_left_mutex, &mattr);
+		pthread_cond_init(&g_ls_cond, NULL);
 
 		pthread_mutexattr_destroy(&mattr);
 
@@ -679,7 +684,6 @@ run_sort(struct sort_list_item **base, size_t nmemb)
 	if (nthreads > 1) {
 		sem_destroy(&mtsem);
 		pthread_mutex_destroy(&g_ls_mutex);
-		pthread_mutex_destroy(&sort_left_mutex);
 	}
 	nthreads = nthreads_save;
 #endif
-- 
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