Hi Jens,
I'm trying to debug a queue stall with your blk-mq-sched branch; with my
latest mpt3sas patches fio stops basically directly after starting a
sequential read :-(
I've debugged things and came up with the attached patch; we need to
restart waiters with blk_mq_tag_idle() after completing a tag.
We're already calling blk_mq_tag_busy() when fetching a tag, so I think
calling blk_mq_tag_idle() is required when retiring a tag.
However, even with the attached patch I'm seeing some queue stalls;
looks like they're related to the 'stonewall' statement in fio.
Debugging continues.
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
From 82b15ff40d71aed318f9946881825f9f03ef8f48 Mon Sep 17 00:00:00 2001
From: Hannes Reinecke <hare@xxxxxxx>
Date: Tue, 24 Jan 2017 14:43:09 +0100
Subject: [PATCH] block-mq: fixup queue stall
__blk_mq_alloc_request() calls blk_mq_tag_busy(), which might result
in the queue to become blocked. So we need to call blk_mq_tag_idle()
once the tag is finished to wakeup all waiters on the queue.
Patch is relative to the blk-mq-sched branch
Signed-off-by: Hannes Reinecke <hare@xxxxxxxx>
---
block/blk-mq.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 739a292..d52bcb1 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -333,10 +333,12 @@ void __blk_mq_finish_request(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
{
const int sched_tag = rq->internal_tag;
struct request_queue *q = rq->q;
+ bool unbusy = false;
- if (rq->rq_flags & RQF_MQ_INFLIGHT)
+ if (rq->rq_flags & RQF_MQ_INFLIGHT) {
atomic_dec(&hctx->nr_active);
-
+ unbusy = true;
+ }
wbt_done(q->rq_wb, &rq->issue_stat);
rq->rq_flags = 0;
@@ -346,6 +348,9 @@ void __blk_mq_finish_request(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
blk_mq_put_tag(hctx, hctx->tags, ctx, rq->tag);
if (sched_tag != -1)
blk_mq_sched_completed_request(hctx, rq);
+ if (unbusy)
+ blk_mq_tag_idle(hctx);
+
blk_queue_exit(q);
}
--
1.8.5.6
