Re: [PATCH] queue stall with blk-mq-sched

[Hannes Reinecke <hare@suse.de>]

On 01/25/2017 08:39 AM, Hannes Reinecke wrote:
> On 01/24/2017 11:06 PM, Jens Axboe wrote:
>> On 01/24/2017 12:55 PM, Jens Axboe wrote:
>>> Try this patch. We only want to bump it for the driver tags, not the
>>> scheduler side.
>>
>> More complete version, this one actually tested. I think this should fix
>> your issue, let me know.
>>
> Nearly there.
> The initial stall is gone, but the test got hung at the 'stonewall'
> sequence again:
> 
> [global]
> bs=4k
> ioengine=libaio
> iodepth=256
> size=4g
> direct=1
> runtime=60
> # directory=/mnt
> numjobs=32
> group_reporting
> cpus_allowed_policy=split
> filename=/dev/md127
> 
> [seq-read]
> rw=read
> -> stonewall
> 
> [rand-read]
> rw=randread
> stonewall
> 
> Restarting all queues made the fio job continue.
> There were 4 queues with state 'restart', and one queue with state 'active'.
> So we're missing a queue run somewhere.
> 
I've found the queue stalls are gone with this patch:

diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
index 6b465bc..de5db6c 100644
--- a/block/blk-mq-sched.h
+++ b/block/blk-mq-sched.h
@@ -113,6 +113,15 @@ static inline void blk_mq_sched_put_rq_priv(struct
request_queue *q,
 }

 static inline void
+blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
+{
+       if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state)) {
+               clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
+               blk_mq_run_hw_queue(hctx, true);
+       }
+}
+
+static inline void
 blk_mq_sched_completed_request(struct blk_mq_hw_ctx *hctx, struct
request *rq)
 {
        struct elevator_queue *e = hctx->queue->elevator;
@@ -123,11 +132,6 @@ static inline void blk_mq_sched_put_rq_priv(struct
request_queue *q,
        BUG_ON(rq->internal_tag == -1);

        blk_mq_put_tag(hctx, hctx->sched_tags, rq->mq_ctx,
rq->internal_tag);
-
-       if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state)) {
-               clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
-               blk_mq_run_hw_queue(hctx, true);
-       }
 }

 static inline void blk_mq_sched_started_request(struct request *rq)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index e872555..63799ad 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -345,6 +345,7 @@ 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);
+       blk_mq_sched_restart(hctx);
        blk_queue_exit(q);
 }

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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