MFC r259659, r259662:

Remove several linear list traversals per request from RPC server code.

  Do not insert active ports into pool->sp_active list if they are success-
fully assigned to some thread.  This makes that list include only ports that
really require attention, and so traversal can be reduced to simple taking
the first one.

  Remove idle thread from pool->sp_idlethreads list when assigning some
work (port of requests) to it.  That again makes possible to replace list
traversals with simple taking the first element.

2 files changed, 46 insertions, 41 deletions

diff --git a/sys/rpc/svc.c b/sys/rpc/svc.c
index 5b48086..96d011a 100644
--- a/sys/rpc/svc.c
+++ b/sys/rpc/svc.c
@@ -293,12 +293,10 @@ xprt_unregister_locked(SVCXPRT *xprt)
 {
 	SVCPOOL *pool = xprt->xp_pool;
 
+	mtx_assert(&pool->sp_lock, MA_OWNED);
 	KASSERT(xprt->xp_registered == TRUE,
 	    ("xprt_unregister_locked: not registered"));
-	if (xprt->xp_active) {
-		TAILQ_REMOVE(&pool->sp_active, xprt, xp_alink);
-		xprt->xp_active = FALSE;
-	}
+	xprt_inactive_locked(xprt);
 	TAILQ_REMOVE(&pool->sp_xlist, xprt, xp_link);
 	xprt->xp_registered = FALSE;
 }
@@ -320,25 +318,25 @@ xprt_unregister(SVCXPRT *xprt)
 	SVC_RELEASE(xprt);
 }
 
-static void
+/*
+ * Attempt to assign a service thread to this transport.
+ */
+static int
 xprt_assignthread(SVCXPRT *xprt)
 {
 	SVCPOOL *pool = xprt->xp_pool;
 	SVCTHREAD *st;
 
-	/*
-	 * Attempt to assign a service thread to this
-	 * transport.
-	 */
-	LIST_FOREACH(st, &pool->sp_idlethreads, st_ilink) {
-		if (st->st_xprt == NULL && STAILQ_EMPTY(&st->st_reqs))
-			break;
-	}
+	mtx_assert(&pool->sp_lock, MA_OWNED);
+	st = LIST_FIRST(&pool->sp_idlethreads);
 	if (st) {
+		LIST_REMOVE(st, st_ilink);
+		st->st_idle = FALSE;
 		SVC_ACQUIRE(xprt);
 		xprt->xp_thread = st;
 		st->st_xprt = xprt;
 		cv_signal(&st->st_cond);
+		return (TRUE);
 	} else {
 		/*
 		 * See if we can create a new thread. The
@@ -354,6 +352,7 @@ xprt_assignthread(SVCXPRT *xprt)
 			pool->sp_state = SVCPOOL_THREADWANTED;
 		}
 	}
+	return (FALSE);
 }
 
 void
@@ -372,9 +371,12 @@ xprt_active(SVCXPRT *xprt)
 	}
 
 	if (!xprt->xp_active) {
-		TAILQ_INSERT_TAIL(&pool->sp_active, xprt, xp_alink);
 		xprt->xp_active = TRUE;
-		xprt_assignthread(xprt);
+		if (xprt->xp_thread == NULL) {
+			if (!xprt_assignthread(xprt))
+				TAILQ_INSERT_TAIL(&pool->sp_active, xprt,
+				    xp_alink);
+		}
 	}
 
 	mtx_unlock(&pool->sp_lock);
@@ -385,8 +387,10 @@ xprt_inactive_locked(SVCXPRT *xprt)
 {
 	SVCPOOL *pool = xprt->xp_pool;
 
+	mtx_assert(&pool->sp_lock, MA_OWNED);
 	if (xprt->xp_active) {
-		TAILQ_REMOVE(&pool->sp_active, xprt, xp_alink);
+		if (xprt->xp_thread == NULL)
+			TAILQ_REMOVE(&pool->sp_active, xprt, xp_alink);
 		xprt->xp_active = FALSE;
 	}
 }
@@ -948,10 +952,11 @@ svc_assign_waiting_sockets(SVCPOOL *pool)
 {
 	SVCXPRT *xprt;
 
-	TAILQ_FOREACH(xprt, &pool->sp_active, xp_alink) {
-		if (!xprt->xp_thread) {
-			xprt_assignthread(xprt);
-		}
+	while ((xprt = TAILQ_FIRST(&pool->sp_active)) != NULL) {
+		if (xprt_assignthread(xprt))
+			TAILQ_REMOVE(&pool->sp_active, xprt, xp_alink);
+		else
+			break;
 	}
 }
 
@@ -1042,21 +1047,17 @@ svc_run_internal(SVCPOOL *pool, bool_t ismaster)
 			 * active transport which isn't being serviced
 			 * by a thread.
 			 */
-			if (svc_request_space_available(pool)) {
-				TAILQ_FOREACH(xprt, &pool->sp_active,
-				    xp_alink) {
-					if (!xprt->xp_thread) {
-						SVC_ACQUIRE(xprt);
-						xprt->xp_thread = st;
-						st->st_xprt = xprt;
-						break;
-					}
-				}
-			}
-			if (st->st_xprt)
+			if (svc_request_space_available(pool) &&
+			    (xprt = TAILQ_FIRST(&pool->sp_active)) != NULL) {
+				TAILQ_REMOVE(&pool->sp_active, xprt, xp_alink);
+				SVC_ACQUIRE(xprt);
+				xprt->xp_thread = st;
+				st->st_xprt = xprt;
 				continue;
+			}
 
 			LIST_INSERT_HEAD(&pool->sp_idlethreads, st, st_ilink);
+			st->st_idle = TRUE;
 			if (ismaster || (!ismaster &&
 			    pool->sp_threadcount > pool->sp_minthreads))
 				error = cv_timedwait_sig(&st->st_cond,
@@ -1064,7 +1065,10 @@ svc_run_internal(SVCPOOL *pool, bool_t ismaster)
 			else
 				error = cv_wait_sig(&st->st_cond,
 				    &pool->sp_lock);
-			LIST_REMOVE(st, st_ilink);
+			if (st->st_idle) {
+				LIST_REMOVE(st, st_ilink);
+				st->st_idle = FALSE;
+			}
 
 			/*
 			 * Reduce worker thread count when idle.
@@ -1132,11 +1136,12 @@ svc_run_internal(SVCPOOL *pool, bool_t ismaster)
 					 * execute the request
 					 * immediately.
 					 */
-					if (stpref != st) {
-						cv_signal(&stpref->st_cond);
-						continue;
-					} else {
+					if (stpref == st)
 						break;
+					if (stpref->st_idle) {
+						LIST_REMOVE(stpref, st_ilink);
+						stpref->st_idle = FALSE;
+						cv_signal(&stpref->st_cond);
 					}
 				}
 			} while (stat == XPRT_MOREREQS
@@ -1153,10 +1158,9 @@ svc_run_internal(SVCPOOL *pool, bool_t ismaster)
 			xprt->xp_thread = NULL;
 			st->st_xprt = NULL;
 			if (xprt->xp_active) {
-				xprt_assignthread(xprt);
-				TAILQ_REMOVE(&pool->sp_active, xprt, xp_alink);
-				TAILQ_INSERT_TAIL(&pool->sp_active, xprt,
-				    xp_alink);
+				if (!xprt_assignthread(xprt))
+					TAILQ_INSERT_TAIL(&pool->sp_active,
+					    xprt, xp_alink);
 			}
 			mtx_unlock(&pool->sp_lock);
 			SVC_RELEASE(xprt);
diff --git a/sys/rpc/svc.h b/sys/rpc/svc.h
index 28a3c5d..0b2884f 100644
--- a/sys/rpc/svc.h
+++ b/sys/rpc/svc.h
@@ -278,6 +278,7 @@ typedef struct __rpc_svcthread {
 	SVCXPRT			*st_xprt; /* transport we are processing */
 	struct svc_reqlist	st_reqs;  /* RPC requests to execute */
 	int			st_reqcount; /* number of queued reqs */
+	int			st_idle; /* thread is on idle list */
 	struct cv		st_cond; /* sleeping for work */
 	LIST_ENTRY(__rpc_svcthread) st_link; /* all threads list */
 	LIST_ENTRY(__rpc_svcthread) st_ilink; /* idle threads list */