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[v2] blk-mq: Explain when 'active_queues' is decremented

Message ID 20170818154835.12034-1-bart.vanassche@wdc.com (mailing list archive)
State New, archived
Headers show

Commit Message

Bart Van Assche Aug. 18, 2017, 3:48 p.m. UTC
It is nontrivial to derive from the blk-mq source code when
blk_mq_tags.active_queues is decremented. Hence add a comment that
explains this.

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
---

v2: Rewrote the comment based on feedback from Jens.

 block/blk-mq.c | 6 ++++++
 1 file changed, 6 insertions(+)
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Patch

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f84d145490bf..09ee74056f93 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -834,6 +834,12 @@  static void blk_mq_timeout_work(struct work_struct *work)
 	} else {
 		struct blk_mq_hw_ctx *hctx;
 
+		/*
+		 * Request timeouts are handled as a forward rolling timer. If
+		 * we end up here it means that no requests are pending and
+		 * also that no request has been pending for a while. Mark
+		 * each hctx as idle.
+		 */
 		queue_for_each_hw_ctx(q, hctx, i) {
 			/* the hctx may be unmapped, so check it here */
 			if (blk_mq_hw_queue_mapped(hctx))