lightnvm: pblk: sched. metadata on write thread

At the moment, line metadata is persisted on a separate work queue, that
is kicked each time that a line is closed. The assumption when designing
this was that freeing the write thread from creating a new write request
was better than the potential impact of writes colliding on the media
(user I/O and metadata I/O). Experimentation has proven that this
assumption is wrong; collision can cause up to 25% of bandwidth and
introduce long tail latencies on the write thread, which potentially
cause user write threads to spend more time spinning to get a free entry
on the write buffer.

This patch moves the metadata logic to the write thread. When a line is
closed, remaining metadata is written in memory and is placed on a
metadata queue. The write thread then takes the metadata corresponding
to the previous line, creates the write request and schedules it to
minimize collisions on the media. Using this approach, we see that we
can saturate the media's bandwidth, which helps reducing both write
latencies and the spinning time for user writer threads.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <matias@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 11 insertions, 5 deletions

diff --git a/drivers/lightnvm/pblk-sysfs.c b/drivers/lightnvm/pblk-sysfs.c
index bf8fc6699299..707d1b91bde6 100644
--- a/drivers/lightnvm/pblk-sysfs.c
+++ b/drivers/lightnvm/pblk-sysfs.c
@@ -150,7 +150,7 @@ static ssize_t pblk_sysfs_lines(struct pblk *pblk, char *page)
 	ssize_t sz = 0;
 	int nr_free_lines;
 	int cur_data, cur_log;
-	int free_line_cnt = 0, closed_line_cnt = 0;
+	int free_line_cnt = 0, closed_line_cnt = 0, emeta_line_cnt = 0;
 	int d_line_cnt = 0, l_line_cnt = 0;
 	int gc_full = 0, gc_high = 0, gc_mid = 0, gc_low = 0, gc_empty = 0;
 	int free = 0, bad = 0, cor = 0;
@@ -166,6 +166,11 @@ static ssize_t pblk_sysfs_lines(struct pblk *pblk, char *page)
 		free_line_cnt++;
 	spin_unlock(&l_mg->free_lock);
 
+	spin_lock(&l_mg->close_lock);
+	list_for_each_entry(line, &l_mg->emeta_list, list)
+		emeta_line_cnt++;
+	spin_unlock(&l_mg->close_lock);
+
 	spin_lock(&l_mg->gc_lock);
 	list_for_each_entry(line, &l_mg->gc_full_list, list) {
 		if (line->type == PBLK_LINETYPE_DATA)
@@ -225,7 +230,7 @@ static ssize_t pblk_sysfs_lines(struct pblk *pblk, char *page)
 		cur_sec = l_mg->data_line->cur_sec;
 		msecs = l_mg->data_line->left_msecs;
 		ssecs = l_mg->data_line->left_ssecs;
-		vsc = l_mg->data_line->vsc;
+		vsc = le32_to_cpu(*l_mg->data_line->vsc);
 		sec_in_line = l_mg->data_line->sec_in_line;
 		meta_weight = bitmap_weight(&l_mg->meta_bitmap,
 							PBLK_DATA_LINES);
@@ -242,10 +247,11 @@ static ssize_t pblk_sysfs_lines(struct pblk *pblk, char *page)
 		geo->nr_luns, lm->blk_per_line, lm->sec_per_line);
 
 	sz += snprintf(page + sz, PAGE_SIZE - sz,
-		"lines:d:%d,l:%d-f:%d(%d),b:%d,co:%d,c:%d(d:%d,l:%d)t:%d\n",
+		"lines:d:%d,l:%d-f:%d(%d),m:%d,c:%d,b:%d,co:%d(d:%d,l:%d)t:%d\n",
 					cur_data, cur_log,
-					free, nr_free_lines, bad, cor,
+					free, nr_free_lines, emeta_line_cnt,
 					closed_line_cnt,
+					bad, cor,
 					d_line_cnt, l_line_cnt,
 					l_mg->nr_lines);
 
@@ -274,7 +280,7 @@ static ssize_t pblk_sysfs_lines_info(struct pblk *pblk, char *page)
 					lm->smeta_len, lm->smeta_sec);
 	sz += snprintf(page + sz, PAGE_SIZE - sz,
 				"emeta - len:%d, sec:%d, bb_start:%d\n",
-					lm->emeta_len, lm->emeta_sec,
+					lm->emeta_len[0], lm->emeta_sec[0],
 					lm->emeta_bb);
 	sz += snprintf(page + sz, PAGE_SIZE - sz,
 				"bitmap lengths: sec:%d, blk:%d, lun:%d\n",