[PATCH -next RFC v2 1/8] sbitmap: record the number of waiters for each waitqueue

[Yu Kuai]

Add a counter in struct sbq_wait_stat to recored how many threads are
waiting on the waitqueue, this will be used in later patches to make
sure 8 waitqueues are balanced. Such counter will also be shown in
debugfs so that user can see if waitqueues are balanced.

Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 include/linux/sbitmap.h | 5 +++++
 lib/sbitmap.c           | 7 +++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index 8f5a86e210b9..8a64271d0696 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -91,6 +91,11 @@ struct sbq_wait_state {
 	 */
 	atomic_t wait_cnt;
 
+	/**
+	 * @waiters_cnt: Number of active waiters
+	 */
+	atomic_t waiters_cnt;
+
 	/**
 	 * @wait: Wait queue.
 	 */
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index ae4fd4de9ebe..393f2b71647a 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -444,6 +444,7 @@ int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
 	for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 		init_waitqueue_head(&sbq->ws[i].wait);
 		atomic_set(&sbq->ws[i].wait_cnt, sbq->wake_batch);
+		atomic_set(&sbq->ws[i].waiters_cnt, 0);
 	}
 
 	return 0;
@@ -759,9 +760,9 @@ void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m)
 	for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 		struct sbq_wait_state *ws = &sbq->ws[i];
 
-		seq_printf(m, "\t{.wait_cnt=%d, .wait=%s},\n",
+		seq_printf(m, "\t{.wait_cnt=%d, .waiters_cnt=%d},\n",
 			   atomic_read(&ws->wait_cnt),
-			   waitqueue_active(&ws->wait) ? "active" : "inactive");
+			   atomic_read(&ws->waiters_cnt));
 	}
 	seq_puts(m, "}\n");
 
@@ -798,6 +799,7 @@ void sbitmap_prepare_to_wait(struct sbitmap_queue *sbq,
 {
 	if (!sbq_wait->sbq) {
 		atomic_inc(&sbq->ws_active);
+		atomic_inc(&ws->waiters_cnt);
 		sbq_wait->sbq = sbq;
 	}
 	prepare_to_wait_exclusive(&ws->wait, &sbq_wait->wait, state);
@@ -810,6 +812,7 @@ void sbitmap_finish_wait(struct sbitmap_queue *sbq, struct sbq_wait_state *ws,
 	finish_wait(&ws->wait, &sbq_wait->wait);
 	if (sbq_wait->sbq) {
 		atomic_dec(&sbq->ws_active);
+		atomic_dec(&ws->waiters_cnt);
 		sbq_wait->sbq = NULL;
 	}
 }
-- 
2.31.1