Index: linux-2.6-git/include/linux/sysctl.h
===================================================================
--- linux-2.6-git.orig/include/linux/sysctl.h	2010-02-05 16:48:08.000000000 +0100
+++ linux-2.6-git/include/linux/sysctl.h	2010-02-05 16:48:50.000000000 +0100
@@ -68,6 +68,7 @@
 	CTL_BUS=8,		/* Busses */
 	CTL_ABI=9,		/* Binary emulation */
 	CTL_CPU=10,		/* CPU stuff (speed scaling, etc) */
+  	CTL_PERF=11,		/* Performance counters and timer sums for debugging */
 	CTL_ARLAN=254,		/* arlan wireless driver */
 	CTL_S390DBF=5677,	/* s390 debug */
 	CTL_SUNRPC=7249,	/* sunrpc debug */
Index: linux-2.6-git/kernel/sysctl.c
===================================================================
--- linux-2.6-git.orig/kernel/sysctl.c	2010-02-05 16:48:08.000000000 +0100
+++ linux-2.6-git/kernel/sysctl.c	2010-02-05 16:48:27.000000000 +0100
@@ -183,6 +183,7 @@
 	.default_set.list = LIST_HEAD_INIT(root_table_header.ctl_entry),
 };
 
+static struct ctl_table perf_table[];
 static struct ctl_table kern_table[];
 static struct ctl_table vm_table[];
 static struct ctl_table fs_table[];
@@ -236,6 +237,13 @@
 		.mode		= 0555,
 		.child		= dev_table,
 	},
+	{
+		.ctl_name	= CTL_PERF,
+		.procname	= "perf",
+		.mode		= 0555,
+		.child		= perf_table,
+	},
+
 /*
  * NOTE: do not add new entries to this table unless you have read
  * Documentation/sysctl/ctl_unnumbered.txt
@@ -250,6 +258,19 @@
 static int max_wakeup_granularity_ns = NSEC_PER_SEC;	/* 1 second */
 #endif
 
+extern unsigned long perf_count_congestion_wait;
+static struct ctl_table perf_table[] = {
+	{
+		.ctl_name	= CTL_UNNUMBERED,
+		.procname       = "perf_count_congestion_wait",
+		.data           = &perf_count_congestion_wait,
+		.mode           = 0666,
+		.maxlen		= sizeof(unsigned long),
+		.proc_handler   = &proc_doulongvec_minmax,
+	},
+	{ .ctl_name = 0 }
+};
+
 static struct ctl_table kern_table[] = {
 	{
 		.ctl_name	= CTL_UNNUMBERED,
Index: linux-2.6-git/mm/backing-dev.c
===================================================================
--- linux-2.6-git.orig/mm/backing-dev.c	2010-02-05 16:48:08.000000000 +0100
+++ linux-2.6-git/mm/backing-dev.c	2010-02-05 16:48:27.000000000 +0100
@@ -739,6 +739,7 @@
 }
 EXPORT_SYMBOL(set_bdi_congested);
 
+unsigned long perf_count_congestion_wait = 0;
 /**
  * congestion_wait - wait for a backing_dev to become uncongested
  * @sync: SYNC or ASYNC IO
@@ -754,6 +755,7 @@
 	DEFINE_WAIT(wait);
 	wait_queue_head_t *wqh = &congestion_wqh[sync];
 
+	perf_count_congestion_wait++;
 	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 	ret = io_schedule_timeout(timeout);
 	finish_wait(wqh, &wait);