Re: [PATCH] blk-mq: only run mapped hw queues in blk_mq_run_hw_queues()

[Jens Axboe <axboe@kernel.dk>]

On 3/28/18 1:45 AM, Christian Borntraeger wrote:
> FWIW, this patch does not fix the issue for me:

Looks like I didn't do the delayed path. How about the below?


diff --git a/block/blk-mq.c b/block/blk-mq.c
index 16e83e6df404..fd663ae1094c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1302,10 +1302,23 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
 	return (queued + errors) != 0;
 }
 
+static bool blk_mq_bail_unmapped(struct blk_mq_hw_ctx *hctx)
+{
+	/*
+	 * Warn if the queue isn't mapped AND we have pending IO. Not being
+	 * mapped isn't necessarily a huge issue, if we don't have pending IO.
+	 */
+	return !blk_mq_hw_queue_mapped(hctx) &&
+		!WARN_ON_ONCE(blk_mq_hctx_has_pending(hctx));
+}
+
 static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
 {
 	int srcu_idx;
 
+	if (blk_mq_bail_unmapped(hctx))
+		return;
+
 	/*
 	 * We should be running this queue from one of the CPUs that
 	 * are mapped to it.
@@ -1399,9 +1412,8 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
 static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
 					unsigned long msecs)
 {
-	if (WARN_ON_ONCE(!blk_mq_hw_queue_mapped(hctx)))
+	if (blk_mq_bail_unmapped(hctx))
 		return;
-
 	if (unlikely(blk_mq_hctx_stopped(hctx)))
 		return;
 

-- 
Jens Axboe