diff --git a/lib/libthr/Makefile b/lib/libthr/Makefile
--- a/lib/libthr/Makefile
+++ b/lib/libthr/Makefile
@@ -44,6 +44,14 @@
 CFLAGS+=-D_PTHREAD_FORCED_UNWIND
 .endif
 
+.if ${MACHINE_ABI:Mlong64}
+# Specify the number of elements in the per-thread pshared lock lookup
+# cache (set it to zero to disable).  This directly affects the size
+# of struct pthread, so keep it small and prime for best results.
+#
+CFLAGS+=-D_PTHREAD_PSC_SIZE=11
+.endif
+
 LDFLAGS+=-Wl,-znodelete
 
 VERSION_DEF=${SRCTOP}/lib/libc/Versions.def
diff --git a/lib/libthr/thread/thr_private.h b/lib/libthr/thread/thr_private.h
--- a/lib/libthr/thread/thr_private.h
+++ b/lib/libthr/thread/thr_private.h
@@ -361,6 +361,17 @@
 	void            (*destructor)(void *);
 };
 
+#if (_PTHREAD_PSC_SIZE > 0)
+/*
+ * Per-thread pshared lock lookup cache entry.
+ */
+struct pthread_psc_entry {
+	u_long htgen;
+	void *key;
+	void *val;
+};
+#endif
+
 /*
  * lwpid_t is 32bit but kernel thr API exports tid as long type
  * to preserve the ABI for M:N model in very early date (r131431).
@@ -532,6 +543,13 @@
 	int			unwind_disabled;
 #endif
 
+#if (_PTHREAD_PSC_SIZE > 0)
+	/*
+	 * Per-thread pshared lock lookup cache hash table.
+	 */
+	struct pthread_psc_entry psc_ht[_PTHREAD_PSC_SIZE];
+#endif
+
 	/*
 	 * Magic value to help recognize a valid thread structure
 	 * from an invalid one:
diff --git a/lib/libthr/thread/thr_pshared.c b/lib/libthr/thread/thr_pshared.c
--- a/lib/libthr/thread/thr_pshared.c
+++ b/lib/libthr/thread/thr_pshared.c
@@ -52,6 +52,24 @@
 static struct urwlock pshared_lock = DEFAULT_URWLOCK;
 static int page_size;
 
+#if (_PTHREAD_PSC_SIZE > 0)
+/*
+ * The pshared_hash[] hash table generation count is advanced/invalidated each
+ * time an entry is removed from the hash table.  Threads performing a lookup
+ * will invalidate affected entries in their private cache when they detect
+ * that pshared_htgen has changed.
+ *
+ * Note that a thread performing a lookup running concurrently with a thread
+ * removing the same key could find and return a stale value (regardless of
+ * whether the pshared lock cache is enabled).  This is a program error.
+ */
+static u_long pshared_htgen;
+
+#define PSHARED_HTGEN_INVALIDATE()	atomic_add_rel_long(&pshared_htgen, 1)
+#else
+#define PSHARED_HTGEN_INVALIDATE()
+#endif
+
 void
 __thr_pshared_init(void)
 {
@@ -116,6 +134,7 @@
 			    h->val, NULL);
 			if (error == 0)
 				continue;
+			PSHARED_HTGEN_INVALIDATE();
 			LIST_REMOVE(h, link);
 			munmap(h->val, page_size);
 			free(h);
@@ -125,17 +144,43 @@
 }
 
 static void *
-pshared_lookup(void *key)
+pshared_lookup(struct pthread *curthread, void *key)
 {
 	struct pshared_hash_head *hd;
 	struct psh *h;
+	void *val;
+
+#if (_PTHREAD_PSC_SIZE > 0)
+	struct pthread_psc_entry *entry;
+	u_long htgen;
+
+	entry = &curthread->psc_ht[(uintptr_t)key % _PTHREAD_PSC_SIZE];
+	htgen = atomic_load_acq_long(&pshared_htgen);
+
+	if (__predict_true(entry->htgen == htgen && entry->key == key))
+		return (entry->val);
+#endif
 
+	pshared_rlock(curthread);
 	hd = &pshared_hash[PSHARED_KEY_HASH(key)];
+	val = NULL;
 	LIST_FOREACH(h, hd, link) {
-		if (h->key == key)
-			return (h->val);
+		if (h->key == key) {
+			val = h->val;
+			break;
+		}
 	}
-	return (NULL);
+	pshared_unlock(curthread);
+
+#if (_PTHREAD_PSC_SIZE > 0)
+	if (val != NULL) {
+		entry->htgen = htgen;
+		entry->key = key;
+		entry->val = val;
+	}
+#endif
+
+	return (val);
 }
 
 static int
@@ -195,6 +240,7 @@
 	hd = &pshared_hash[PSHARED_KEY_HASH(key)];
 	LIST_FOREACH(h, hd, link) {
 		if (h->key == key) {
+			PSHARED_HTGEN_INVALIDATE();
 			LIST_REMOVE(h, link);
 			val = h->val;
 			free(h);
@@ -232,13 +278,11 @@
 	int fd, ins_done;
 
 	curthread = _get_curthread();
-	if (doalloc) {
+	if (__predict_false(doalloc)) {
 		pshared_destroy(curthread, key);
 		res = NULL;
 	} else {
-		pshared_rlock(curthread);
-		res = pshared_lookup(key);
-		pshared_unlock(curthread);
+		res = pshared_lookup(curthread, key);
 		if (res != NULL)
 			return (res);
 	}
@@ -275,6 +319,7 @@
 {
 
 	_thr_rwl_rdlock(&pshared_lock);
+	PSHARED_HTGEN_INVALIDATE();
 }
 
 void