[PATCH] md/raid5: Add compensation in sysfs for raid456.

[majianpeng <majianpeng@gmail.com>]

For non-fullstripe-write, raid456 need read some old data no matter how
rcw or rmw. We use compensation to recored the value about the
additional read-data.The unit of compenstaion is PAGE_SIZE.
Using the formula compensation*PAGE_SIZE/write_count_for_md, we can know
the efficiency.Using this we can tune the write mode to get the best
efficiency.

Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
---
 drivers/md/raid5.c |   16 ++++++++++++++++
 drivers/md/raid5.h |    5 +++++
 2 files changed, 21 insertions(+)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index cc055da..e456134 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3116,6 +3116,7 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 						 "%d for r-m-w\n", i);
 					set_bit(R5_LOCKED, &dev->flags);
 					set_bit(R5_Wantread, &dev->flags);
+					atomic_inc(&conf->compensation);
 					s->locked++;
 				} else {
 					set_bit(STRIPE_DELAYED, &sh->state);
@@ -3144,6 +3145,7 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 						"%d for Reconstruct\n", i);
 					set_bit(R5_LOCKED, &dev->flags);
 					set_bit(R5_Wantread, &dev->flags);
+					atomic_inc(&conf->compensation);
 					s->locked++;
 					qread++;
 				} else {
@@ -5426,12 +5428,25 @@ static struct md_sysfs_entry
 raid5_group_thread_cnt = __ATTR(group_thread_cnt, S_IRUGO | S_IWUSR,
 				raid5_show_group_thread_cnt,
 				raid5_store_group_thread_cnt);
+static ssize_t
+compensation_show(struct mddev *mddev, char *page)
+{
+	struct r5conf *conf = mddev->private;
+	if (conf)
+		return sprintf(page, "%d\n", atomic_read(&conf->compensation));
+	else
+		return 0;
+}
+
+static struct md_sysfs_entry
+raid5_compensation = __ATTR_RO(compensation);
 
 static struct attribute *raid5_attrs[] =  {
 	&raid5_stripecache_size.attr,
 	&raid5_stripecache_active.attr,
 	&raid5_preread_bypass_threshold.attr,
 	&raid5_group_thread_cnt.attr,
+	&raid5_compensation.attr,
 	NULL,
 };
 static struct attribute_group raid5_attrs_group = {
@@ -5686,6 +5701,7 @@ static struct r5conf *setup_conf(struct mddev *mddev)
 	atomic_set(&conf->active_stripes, 0);
 	atomic_set(&conf->preread_active_stripes, 0);
 	atomic_set(&conf->active_aligned_reads, 0);
+	atomic_set(&conf->compensation, 0);
 	conf->bypass_threshold = BYPASS_THRESHOLD;
 	conf->recovery_disabled = mddev->recovery_disabled - 1;
 
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 01ad8ae..8fa538d 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -494,6 +494,11 @@ struct r5conf {
 	struct r5worker_group	*worker_groups;
 	int			group_cnt;
 	int			worker_cnt_per_group;
+
+	/*For non-fullstripe-write, it need read some data
+	 * using this filed to acount the additional data.
+	 * The unit of compensation is PAGE_SIZE*/
+	atomic_t		compensation;
 };
 
 /*
-- 
1.7.10.4