svn commit: r197024 - stable/8/sys/kern

Attilio Rao attilio at FreeBSD.org
Wed Sep 9 09:34:13 UTC 2009


Author: attilio
Date: Wed Sep  9 09:34:13 2009
New Revision: 197024
URL: http://svn.freebsd.org/changeset/base/197024

Log:
  Adaptive spinning for locking primitives, in read-mode, have some tuning
  SYSCTLs which are inappropriate for a daily use of the machine (mostly
  useful only by a developer which wants to run benchmarks on it).
  Remove them before the release as long as we do not want to ship with
  them in.
  
  Now that the SYSCTLs are gone, instead than use static storage for some
  constants, use real numeric constants in order to avoid eventual compiler
  dumbiness and the risk to share a storage (and then a cache-line) among
  CPUs when doing adaptive spinning together.
  
  Pleasse note that the sys/linker_set.h inclusion in lockmgr and sx lock
  support could have been gone, but re@ preferred them to be in order to
  minimize the risk of problems on future merging.
  
  Please note that this patch is not a MFC, but an 'edge case' as commit
  directly to stable/8, which creates a diverging from HEAD.
  
  Tested by:      Giovanni Trematerra <giovanni dot trematerra at gmail dot com>
  Approved by:	re (kib)

Modified:
  stable/8/sys/kern/kern_lock.c
  stable/8/sys/kern/kern_rwlock.c
  stable/8/sys/kern/kern_sx.c

Modified: stable/8/sys/kern/kern_lock.c
==============================================================================
--- stable/8/sys/kern/kern_lock.c	Wed Sep  9 09:17:31 2009	(r197023)
+++ stable/8/sys/kern/kern_lock.c	Wed Sep  9 09:34:13 2009	(r197024)
@@ -62,6 +62,11 @@ CTASSERT(LK_UNLOCKED == (LK_UNLOCKED &
 #define	SQ_EXCLUSIVE_QUEUE	0
 #define	SQ_SHARED_QUEUE		1
 
+#ifdef ADAPTIVE_LOCKMGRS
+#define	ALK_RETRIES		10
+#define	ALK_LOOPS		10000
+#endif
+
 #ifndef INVARIANTS
 #define	_lockmgr_assert(lk, what, file, line)
 #define	TD_LOCKS_INC(td)
@@ -156,14 +161,6 @@ struct lock_class lock_class_lockmgr = {
 #endif
 };
 
-#ifdef ADAPTIVE_LOCKMGRS
-static u_int alk_retries = 10;
-static u_int alk_loops = 10000;
-SYSCTL_NODE(_debug, OID_AUTO, lockmgr, CTLFLAG_RD, NULL, "lockmgr debugging");
-SYSCTL_UINT(_debug_lockmgr, OID_AUTO, retries, CTLFLAG_RW, &alk_retries, 0, "");
-SYSCTL_UINT(_debug_lockmgr, OID_AUTO, loops, CTLFLAG_RW, &alk_loops, 0, "");
-#endif
-
 static __inline struct thread *
 lockmgr_xholder(struct lock *lk)
 {
@@ -498,14 +495,14 @@ __lockmgr_args(struct lock *lk, u_int fl
 				continue;
 			} else if (LK_CAN_ADAPT(lk, flags) &&
 			    (x & LK_SHARE) != 0 && LK_SHARERS(x) &&
-			    spintries < alk_retries) {
+			    spintries < ALK_RETRIES) {
 				if (flags & LK_INTERLOCK) {
 					class->lc_unlock(ilk);
 					flags &= ~LK_INTERLOCK;
 				}
 				GIANT_SAVE();
 				spintries++;
-				for (i = 0; i < alk_loops; i++) {
+				for (i = 0; i < ALK_LOOPS; i++) {
 					if (LOCK_LOG_TEST(&lk->lock_object, 0))
 						CTR4(KTR_LOCK,
 				    "%s: shared spinning on %p with %u and %u",
@@ -517,7 +514,7 @@ __lockmgr_args(struct lock *lk, u_int fl
 					cpu_spinwait();
 				}
 				GIANT_RESTORE();
-				if (i != alk_loops)
+				if (i != ALK_LOOPS)
 					continue;
 			}
 #endif
@@ -714,7 +711,7 @@ __lockmgr_args(struct lock *lk, u_int fl
 				continue;
 			} else if (LK_CAN_ADAPT(lk, flags) &&
 			    (x & LK_SHARE) != 0 && LK_SHARERS(x) &&
-			    spintries < alk_retries) {
+			    spintries < ALK_RETRIES) {
 				if ((x & LK_EXCLUSIVE_SPINNERS) == 0 &&
 				    !atomic_cmpset_ptr(&lk->lk_lock, x,
 				    x | LK_EXCLUSIVE_SPINNERS))
@@ -725,7 +722,7 @@ __lockmgr_args(struct lock *lk, u_int fl
 				}
 				GIANT_SAVE();
 				spintries++;
-				for (i = 0; i < alk_loops; i++) {
+				for (i = 0; i < ALK_LOOPS; i++) {
 					if (LOCK_LOG_TEST(&lk->lock_object, 0))
 						CTR4(KTR_LOCK,
 				    "%s: shared spinning on %p with %u and %u",
@@ -736,7 +733,7 @@ __lockmgr_args(struct lock *lk, u_int fl
 					cpu_spinwait();
 				}
 				GIANT_RESTORE();
-				if (i != alk_loops)
+				if (i != ALK_LOOPS)
 					continue;
 			}
 #endif

Modified: stable/8/sys/kern/kern_rwlock.c
==============================================================================
--- stable/8/sys/kern/kern_rwlock.c	Wed Sep  9 09:17:31 2009	(r197023)
+++ stable/8/sys/kern/kern_rwlock.c	Wed Sep  9 09:34:13 2009	(r197024)
@@ -56,11 +56,8 @@ __FBSDID("$FreeBSD$");
 #endif
 
 #ifdef ADAPTIVE_RWLOCKS
-static int rowner_retries = 10;
-static int rowner_loops = 10000;
-SYSCTL_NODE(_debug, OID_AUTO, rwlock, CTLFLAG_RD, NULL, "rwlock debugging");
-SYSCTL_INT(_debug_rwlock, OID_AUTO, retry, CTLFLAG_RW, &rowner_retries, 0, "");
-SYSCTL_INT(_debug_rwlock, OID_AUTO, loops, CTLFLAG_RW, &rowner_loops, 0, "");
+#define	ROWNER_RETRIES	10
+#define	ROWNER_LOOPS	10000
 #endif
 
 #ifdef DDB
@@ -380,15 +377,15 @@ _rw_rlock(struct rwlock *rw, const char 
 				}
 				continue;
 			}
-		} else if (spintries < rowner_retries) {
+		} else if (spintries < ROWNER_RETRIES) {
 			spintries++;
-			for (i = 0; i < rowner_loops; i++) {
+			for (i = 0; i < ROWNER_LOOPS; i++) {
 				v = rw->rw_lock;
 				if ((v & RW_LOCK_READ) == 0 || RW_CAN_READ(v))
 					break;
 				cpu_spinwait();
 			}
-			if (i != rowner_loops)
+			if (i != ROWNER_LOOPS)
 				continue;
 		}
 #endif
@@ -690,7 +687,7 @@ _rw_wlock_hard(struct rwlock *rw, uintpt
 			continue;
 		}
 		if ((v & RW_LOCK_READ) && RW_READERS(v) &&
-		    spintries < rowner_retries) {
+		    spintries < ROWNER_RETRIES) {
 			if (!(v & RW_LOCK_WRITE_SPINNER)) {
 				if (!atomic_cmpset_ptr(&rw->rw_lock, v,
 				    v | RW_LOCK_WRITE_SPINNER)) {
@@ -698,15 +695,15 @@ _rw_wlock_hard(struct rwlock *rw, uintpt
 				}
 			}
 			spintries++;
-			for (i = 0; i < rowner_loops; i++) {
+			for (i = 0; i < ROWNER_LOOPS; i++) {
 				if ((rw->rw_lock & RW_LOCK_WRITE_SPINNER) == 0)
 					break;
 				cpu_spinwait();
 			}
 #ifdef KDTRACE_HOOKS
-			spin_cnt += rowner_loops - i;
+			spin_cnt += ROWNER_LOOPS - i;
 #endif
-			if (i != rowner_loops)
+			if (i != ROWNER_LOOPS)
 				continue;
 		}
 #endif

Modified: stable/8/sys/kern/kern_sx.c
==============================================================================
--- stable/8/sys/kern/kern_sx.c	Wed Sep  9 09:17:31 2009	(r197023)
+++ stable/8/sys/kern/kern_sx.c	Wed Sep  9 09:34:13 2009	(r197024)
@@ -72,6 +72,11 @@ CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS)
 #define	SQ_EXCLUSIVE_QUEUE	0
 #define	SQ_SHARED_QUEUE		1
 
+#ifdef ADAPTIVE_SX
+#define	ASX_RETRIES		10
+#define	ASX_LOOPS		10000
+#endif
+
 /*
  * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file.  We
  * drop Giant anytime we have to sleep or if we adaptively spin.
@@ -134,14 +139,6 @@ struct lock_class lock_class_sx = {
 #define	_sx_assert(sx, what, file, line)
 #endif
 
-#ifdef ADAPTIVE_SX
-static u_int asx_retries = 10;
-static u_int asx_loops = 10000;
-SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
-SYSCTL_INT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
-SYSCTL_INT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
-#endif
-
 void
 assert_sx(struct lock_object *lock, int what)
 {
@@ -530,10 +527,10 @@ _sx_xlock_hard(struct sx *sx, uintptr_t 
 					}
 					continue;
 				}
-			} else if (SX_SHARERS(x) && spintries < asx_retries) {
+			} else if (SX_SHARERS(x) && spintries < ASX_RETRIES) {
 				GIANT_SAVE();
 				spintries++;
-				for (i = 0; i < asx_loops; i++) {
+				for (i = 0; i < ASX_LOOPS; i++) {
 					if (LOCK_LOG_TEST(&sx->lock_object, 0))
 						CTR4(KTR_LOCK,
 				    "%s: shared spinning on %p with %u and %u",
@@ -547,7 +544,7 @@ _sx_xlock_hard(struct sx *sx, uintptr_t 
 					spin_cnt++;
 #endif
 				}
-				if (i != asx_loops)
+				if (i != ASX_LOOPS)
 					continue;
 			}
 		}


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