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

[Jens Axboe]

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.

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index a49ec77..1b156ca 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -90,9 +90,11 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
        return atomic_read(&hctx->nr_active) < depth;
 }
 
-static int __blk_mq_get_tag(struct blk_mq_hw_ctx *hctx, struct sbitmap_queue 
*bt)
+static int __blk_mq_get_tag(struct blk_mq_alloc_data *data,
+                           struct sbitmap_queue *bt)
 {
-       if (!hctx_may_queue(hctx, bt))
+       if (!(data->flags & BLK_MQ_REQ_INTERNAL) &&
+           !hctx_may_queue(data->hctx, bt))
                return -1;
        return __sbitmap_queue_get(bt);
 }
@@ -118,7 +120,7 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
                tag_offset = tags->nr_reserved_tags;
        }
 
-       tag = __blk_mq_get_tag(data->hctx, bt);
+       tag = __blk_mq_get_tag(data, bt);
        if (tag != -1)
                goto found_tag;
 
@@ -129,7 +131,7 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
        do {
                prepare_to_wait(&ws->wait, &wait, TASK_UNINTERRUPTIBLE);
 
-               tag = __blk_mq_get_tag(data->hctx, bt);
+               tag = __blk_mq_get_tag(data, bt);
                if (tag != -1)
                        break;
 
@@ -144,7 +146,7 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
                 * Retry tag allocation after running the hardware queue,
                 * as running the queue may also have found completions.
                 */
-               tag = __blk_mq_get_tag(data->hctx, bt);
+               tag = __blk_mq_get_tag(data, bt);
                if (tag != -1)
                        break;
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index ee69e5e..dcb5676 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -230,15 +230,14 @@ struct request *__blk_mq_alloc_request(struct 
blk_mq_alloc_data *data,
 
                rq = tags->static_rqs[tag];
 
-               if (blk_mq_tag_busy(data->hctx)) {
-                       rq->rq_flags = RQF_MQ_INFLIGHT;
-                       atomic_inc(&data->hctx->nr_active);
-               }
-
                if (data->flags & BLK_MQ_REQ_INTERNAL) {
                        rq->tag = -1;
                        rq->internal_tag = tag;
                } else {
+                       if (blk_mq_tag_busy(data->hctx)) {
+                               rq->rq_flags = RQF_MQ_INFLIGHT;
+                               atomic_inc(&data->hctx->nr_active);
+                       }
                        rq->tag = tag;
                        rq->internal_tag = -1;
                }
@@ -869,6 +868,10 @@ static bool blk_mq_get_driver_tag(struct request *rq,
 
        rq->tag = blk_mq_get_tag(&data);
        if (rq->tag >= 0) {
+               if (blk_mq_tag_busy(data.hctx)) {
+                       rq->rq_flags |= RQF_MQ_INFLIGHT;
+                       atomic_inc(&data.hctx->nr_active);
+               }
                data.hctx->tags->rqs[rq->tag] = rq;
                goto done;
        }

-- 
Jens Axboe

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