On 9/11/20 11:44 AM, Ming Lei wrote:
> NVMe shares tagset between fabric queue and admin queue or between
> connect_q and NS queue, so hctx_may_queue() can be called to allocate
> request for these queues.
>
> Tags can be reserved in these tagset. Before error recovery, there is
> often lots of in-flight requests which can't be completed, and new
> reserved request may be needed in error recovery path. However,
> hctx_may_queue() can always return false because there is too many
> in-flight requests which can't be completed during error handling.
> Finally, everything can't move on.
>
> Fix this issue by always allowing reserved tag allocation in
> hctx_may_queue(). This ways is reasonable because reserved tag
> suppose to be ready any time.
>
> Cc: David Milburn <dmilburn@xxxxxxxxxx>
> Cc: Ewan D. Milne <emilne@xxxxxxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> block/blk-mq-tag.c | 3 ++-
> block/blk-mq.c | 6 ++++--
> 2 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> index c31c4a0478a5..aacf10decdbd 100644
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -76,7 +76,8 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
> static int __blk_mq_get_tag(struct blk_mq_alloc_data *data,
> struct sbitmap_queue *bt)
> {
> - if (!data->q->elevator && !hctx_may_queue(data->hctx, bt))
> + if (!data->q->elevator && !(data->flags & BLK_MQ_REQ_RESERVED) &&
> + !hctx_may_queue(data->hctx, bt))
> return BLK_MQ_NO_TAG;
>
> if (data->shallow_depth)
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index ccb500e38008..91cff275451d 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1147,15 +1147,17 @@ static bool __blk_mq_get_driver_tag(struct request *rq)
> struct sbitmap_queue *bt = rq->mq_hctx->tags->bitmap_tags;
> unsigned int tag_offset = rq->mq_hctx->tags->nr_reserved_tags;
> int tag;
> + bool reserved = blk_mq_tag_is_reserved(rq->mq_hctx->sched_tags,
> + rq->internal_tag);
>
> blk_mq_tag_busy(rq->mq_hctx);
>
> - if (blk_mq_tag_is_reserved(rq->mq_hctx->sched_tags, rq->internal_tag)) {
> + if (reserved) {
> bt = rq->mq_hctx->tags->breserved_tags;
> tag_offset = 0;
> }
>
> - if (!hctx_may_queue(rq->mq_hctx, bt))
> + if (!reserved && !hctx_may_queue(rq->mq_hctx, bt))
> return false;
> tag = __sbitmap_queue_get(bt);
> if (tag == BLK_MQ_NO_TAG)
>
Very good point.
Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@xxxxxxx +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer
