[2/2] filtered buffer_head wakeups

[William Lee Irwin III <wli@holomorphy.com>]

On Sun, May 02, 2004 at 07:29:36PM -0700, William Lee Irwin III wrote:
> This patch creates a new scheduling entrypoint, wake_up_filtered(), and
> uses it in page waitqueue hashing to discriminate between the waiters
> on various pages. One of the sources of the thundering herds was
> identified as the page waitqueue hashing by a priori methods and
> empirically confirmed using the scheduler caller profiling patch.

It turned out there were still thundering herds after the page
waitqueue hashtable. The scheduler caller profiling patch identified
this as the buffer_head waitqueue hashtable. This patch teaches the
buffer_head waitqueue hashing to use filtered wakeups.


-- wli

Index: wli-2.6.6-rc3-mm1/fs/buffer.c
===================================================================
--- wli-2.6.6-rc3-mm1.orig/fs/buffer.c	2004-04-30 15:06:46.000000000 -0700
+++ wli-2.6.6-rc3-mm1/fs/buffer.c	2004-04-30 19:51:25.000000000 -0700
@@ -74,7 +74,7 @@
 
 	smp_mb();
 	if (waitqueue_active(wq))
-		wake_up_all(wq);
+		wake_up_filtered(wq, bh);
 }
 EXPORT_SYMBOL(wake_up_buffer);
 
@@ -93,10 +93,10 @@
 void __wait_on_buffer(struct buffer_head * bh)
 {
 	wait_queue_head_t *wqh = bh_waitq_head(bh);
-	DEFINE_WAIT(wait);
+	DEFINE_FILTERED_WAIT(wait, bh);
 
 	do {
-		prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
+		prepare_to_wait(wqh, &wait.wait, TASK_UNINTERRUPTIBLE);
 		if (buffer_locked(bh)) {
 			struct block_device *bd;
 			smp_mb();
@@ -106,7 +106,7 @@
 			io_schedule();
 		}
 	} while (buffer_locked(bh));
-	finish_wait(wqh, &wait);
+	finish_wait(wqh, &wait.wait);
 }
 
 static void
Index: wli-2.6.6-rc3-mm1/fs/jbd/transaction.c
===================================================================
--- wli-2.6.6-rc3-mm1.orig/fs/jbd/transaction.c	2004-04-30 15:06:46.000000000 -0700
+++ wli-2.6.6-rc3-mm1/fs/jbd/transaction.c	2004-04-30 19:51:25.000000000 -0700
@@ -638,7 +638,7 @@
 			jbd_unlock_bh_state(bh);
 			/* commit wakes up all shadow buffers after IO */
 			wqh = bh_waitq_head(jh2bh(jh));
-			wait_event(*wqh, (jh->b_jlist != BJ_Shadow));
+			wait_event_filtered(*wqh, jh2bh(jh), (jh->b_jlist != BJ_Shadow));
 			goto repeat;
 		}
 
Index: wli-2.6.6-rc3-mm1/include/linux/wait.h
===================================================================
--- wli-2.6.6-rc3-mm1.orig/include/linux/wait.h	2004-04-30 19:50:33.000000000 -0700
+++ wli-2.6.6-rc3-mm1/include/linux/wait.h	2004-04-30 19:51:25.000000000 -0700
@@ -146,7 +146,6 @@
 		break;							\
 	__wait_event(wq, condition);					\
 } while (0)
-
 #define __wait_event_interruptible(wq, condition, ret)			\
 do {									\
 	wait_queue_t __wait;						\
@@ -273,7 +272,28 @@
 			.task_list = LIST_HEAD_INIT(name.wait.task_list),\
 		},							\
 	}
-	
+
+#define __wait_event_filtered(wq, key, condition) 			\
+do {									\
+	DEFINE_FILTERED_WAIT(__wait, key);				\
+	add_wait_queue(&(wq), &__wait.wait);				\
+	for (;;) {							\
+		set_current_state(TASK_UNINTERRUPTIBLE);		\
+		if (condition)						\
+			break;						\
+		schedule();						\
+	}								\
+	current->state = TASK_RUNNING;					\
+	remove_wait_queue(&(wq), &__wait.wait);				\
+} while (0)
+
+
+#define wait_event_filtered(wq, key, condition)				\
+do {									\
+	if (!(condition))						\
+		__wait_event_filtered(wq, key, condition);		\
+} while (0)
+
 #endif /* __KERNEL__ */
 
 #endif