[patch] voluntary-preempt-2.6.8-rc2-J4

[Ingo Molnar <mingo@elte.hu>]

i've uploaded the -J4 patch:

   http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.8-rc2-J4

Changes since -J3:

 - make block device max_sectors sysfs tunable. There's a new entry
   /sys/block/*/queue/max_sectors_kb which stores the current max 
   request size in KB. You can write it to change the size.

   Jens: i've attached a standalone patch against 2.6.8-rc2 below. 
   Please apply if it looks good to you. (I've added extra locking to 
   make sure max_sectors and readahead_pages gets updated at once, for 
   the unlikely event of two CPUs updating max_sectors at once.) I've 
   tested this on IDE using the UP kernel.

 - include the unlock-tty changes suggested by akpm and tested by Lee 
   Revell. I've also unlocked the tty_read path - only the release/open 
   paths remain under the big kernel lock. Please report any tty related 
   regressions.

	Ingo

--
introduce max_sectors_kb tunable.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

--- linux/drivers/block/ll_rw_blk.c.orig	
+++ linux/drivers/block/ll_rw_blk.c	
@@ -3062,13 +3063,50 @@ queue_ra_store(struct request_queue *q, 
 	unsigned long ra_kb;
 	ssize_t ret = queue_var_store(&ra_kb, page, count);
 
+	spin_lock_irq(q->queue_lock);
 	if (ra_kb > (q->max_sectors >> 1))
 		ra_kb = (q->max_sectors >> 1);
 
 	q->backing_dev_info.ra_pages = ra_kb >> (PAGE_CACHE_SHIFT - 10);
+	spin_unlock_irq(q->queue_lock);
+
+	return ret;
+}
+
+static ssize_t queue_max_sectors_show(struct request_queue *q, char *page)
+{
+	int max_sectors_kb = q->max_sectors >> 1;
+
+	return queue_var_show(max_sectors_kb, (page));
+}
+
+static ssize_t
+queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
+{
+	unsigned long max_sectors_kb;
+	ssize_t ret = queue_var_store(&max_sectors_kb, page, count);
+	int ra_kb;
+
+	/*
+	 * Take the queue lock to update the readahead and max_sectors
+	 * values synchronously:
+	 */
+	spin_lock_irq(q->queue_lock);
+	/*
+	 * Trim readahead window as well, if necessary:
+	 */
+	ra_kb = q->backing_dev_info.ra_pages << (PAGE_CACHE_SHIFT - 10);
+	if (ra_kb > max_sectors_kb)
+		q->backing_dev_info.ra_pages =
+				max_sectors_kb >> (PAGE_CACHE_SHIFT - 10);
+
+	q->max_sectors = max_sectors_kb << 1;
+	spin_unlock_irq(q->queue_lock);
+
 	return ret;
 }
 
+
 static struct queue_sysfs_entry queue_requests_entry = {
 	.attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
 	.show = queue_requests_show,
@@ -3081,9 +3119,16 @@ static struct queue_sysfs_entry queue_ra
 	.store = queue_ra_store,
 };
 
+static struct queue_sysfs_entry queue_max_sectors_entry = {
+	.attr = {.name = "max_sectors_kb", .mode = S_IRUGO | S_IWUSR },
+	.show = queue_max_sectors_show,
+	.store = queue_max_sectors_store,
+};
+
 static struct attribute *default_attrs[] = {
 	&queue_requests_entry.attr,
 	&queue_ra_entry.attr,
+	&queue_max_sectors_entry.attr,
 	NULL,
 };