Re: [PATCH 8/9] scsi: megaraid: convert private reply queue to blk-mq hw queue

[Ming Lei <ming.lei@redhat.com>]

Hi Kashyap,

Thanks for collecting the log.

On Sun, Jun 02, 2019 at 10:04:01PM +0530, Kashyap Desai wrote:
> > Meantime please try the following patch and see if difference can be
> made.
> >
> > diff --git a/block/blk-mq.c b/block/blk-mq.c index
> > 49d73d979cb3..d2abec3b0f60 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -589,7 +589,7 @@ static void __blk_mq_complete_request(struct
> > request *rq)
> >  	 * So complete IO reqeust in softirq context in case of single
> queue
> >  	 * for not degrading IO performance by irqsoff latency.
> >  	 */
> > -	if (q->nr_hw_queues == 1) {
> > +	if (q->nr_hw_queues == 1 || (rq->mq_hctx->flags &
> > BLK_MQ_F_HOST_TAGS))
> > +{
> >  		__blk_complete_request(rq);
> >  		return;
> >  	}
> > @@ -1977,7 +1977,8 @@ static blk_qc_t blk_mq_make_request(struct
> > request_queue *q, struct bio *bio)
> >  		/* bypass scheduler for flush rq */
> >  		blk_insert_flush(rq);
> >  		blk_mq_run_hw_queue(data.hctx, true);
> > -	} else if (plug && (q->nr_hw_queues == 1 || q->mq_ops-
> > >commit_rqs)) {
> > +	} else if (plug && (q->nr_hw_queues == 1 || q->mq_ops->commit_rqs
> > ||
> > +				(data.hctx->flags & BLK_MQ_F_HOST_TAGS)))
> > {
> >  		/*
> >  		 * Use plugging if we have a ->commit_rqs() hook as well,
> as
> >  		 * we know the driver uses bd->last in a smart fashion.
> 
> Ming -
> 
> I tried above patch and no improvement in performance.
> 
> Below is perf record data - lock contention is while getting the tag
> (blk_mq_get_tag )
> 
> 6.67%     6.67%  fio              [kernel.vmlinux]  [k]
> native_queued_spin_lock_slowpath
>    - 6.66% io_submit
>       - 6.66% entry_SYSCALL_64
>          - do_syscall_64
>             - 6.66% __x64_sys_io_submit
>                - 6.66% io_submit_one
>                   - 6.66% aio_read
>                      - 6.66% generic_file_read_iter
>                         - 6.66% blkdev_direct_IO
>                            - 6.65% submit_bio
>                               - generic_make_request
>                                  - 6.65% blk_mq_make_request
>                                     - 6.65% blk_mq_get_request
>                                        - 6.65% blk_mq_get_tag
>                                           - 6.58%
> prepare_to_wait_exclusive
>                                              - 6.57%
> _raw_spin_lock_irqsave
> 
> queued_spin_lock_slowpath

Please drop the patch in my last email, and apply the following patch
and see if we can make a difference:

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 3d6780504dcb..69d6bffcc8ff 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -627,6 +627,9 @@ static int hctx_active_show(void *data, struct seq_file *m)
 {
 	struct blk_mq_hw_ctx *hctx = data;
 
+	if (hctx->flags & BLK_MQ_F_HOST_TAGS)
+		hctx = blk_mq_master_hctx(hctx);
+
 	seq_printf(m, "%d\n", atomic_read(&hctx->nr_active));
 	return 0;
 }
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 309ec5079f3f..58ef83a34fda 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -30,6 +30,9 @@ bool blk_mq_has_free_tags(struct blk_mq_tags *tags)
  */
 bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
 {
+	if (hctx->flags & BLK_MQ_F_HOST_TAGS)
+		hctx = blk_mq_master_hctx(hctx);
+
 	if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
 	    !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
 		atomic_inc(&hctx->tags->active_queues);
@@ -55,6 +58,9 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
 {
 	struct blk_mq_tags *tags = hctx->tags;
 
+	if (hctx->flags & BLK_MQ_F_HOST_TAGS)
+		hctx = blk_mq_master_hctx(hctx);
+
 	if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
 		return;
 
@@ -74,6 +80,10 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
 
 	if (!hctx || !(hctx->flags & BLK_MQ_F_TAG_SHARED))
 		return true;
+
+	if (hctx->flags & BLK_MQ_F_HOST_TAGS)
+		hctx = blk_mq_master_hctx(hctx);
+
 	if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
 		return true;
 
diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
index 61deab0b5a5a..84e9b46ffc78 100644
--- a/block/blk-mq-tag.h
+++ b/block/blk-mq-tag.h
@@ -36,11 +36,22 @@ extern void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool);
 void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
 		void *priv);
 
+static inline struct blk_mq_hw_ctx *blk_mq_master_hctx(
+		struct blk_mq_hw_ctx *hctx)
+{
+	return hctx->queue->queue_hw_ctx[0];
+}
+
+
 static inline struct sbq_wait_state *bt_wait_ptr(struct sbitmap_queue *bt,
 						 struct blk_mq_hw_ctx *hctx)
 {
 	if (!hctx)
 		return &bt->ws[0];
+
+	if (hctx->flags & BLK_MQ_F_HOST_TAGS)
+		hctx = blk_mq_master_hctx(hctx);
+
 	return sbq_wait_ptr(bt, &hctx->wait_index);
 }
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 49d73d979cb3..4196ed3b0085 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -303,7 +303,7 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
 	} else {
 		if (data->hctx->flags & BLK_MQ_F_TAG_SHARED) {
 			rq_flags = RQF_MQ_INFLIGHT;
-			atomic_inc(&data->hctx->nr_active);
+			blk_mq_inc_nr_active(data->hctx);
 		}
 		rq->tag = tag;
 		rq->internal_tag = -1;
@@ -517,7 +517,7 @@ void blk_mq_free_request(struct request *rq)
 
 	ctx->rq_completed[rq_is_sync(rq)]++;
 	if (rq->rq_flags & RQF_MQ_INFLIGHT)
-		atomic_dec(&hctx->nr_active);
+		blk_mq_dec_nr_active(hctx);
 
 	if (unlikely(laptop_mode && !blk_rq_is_passthrough(rq)))
 		laptop_io_completion(q->backing_dev_info);
@@ -1064,7 +1064,7 @@ bool blk_mq_get_driver_tag(struct request *rq)
 	if (rq->tag >= 0) {
 		if (shared) {
 			rq->rq_flags |= RQF_MQ_INFLIGHT;
-			atomic_inc(&data.hctx->nr_active);
+			blk_mq_inc_nr_active(data.hctx);
 		}
 		data.hctx->tags->rqs[rq->tag] = rq;
 	}
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 633a5a77ee8b..f1279b8c2289 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -193,6 +193,20 @@ unsigned int blk_mq_in_flight(struct request_queue *q, struct hd_struct *part);
 void blk_mq_in_flight_rw(struct request_queue *q, struct hd_struct *part,
 			 unsigned int inflight[2]);
 
+static inline void blk_mq_inc_nr_active(struct blk_mq_hw_ctx *hctx)
+{
+	if (hctx->flags & BLK_MQ_F_HOST_TAGS)
+		hctx = blk_mq_master_hctx(hctx);
+	atomic_inc(&hctx->nr_active);
+}
+
+static inline void blk_mq_dec_nr_active(struct blk_mq_hw_ctx *hctx)
+{
+	if (hctx->flags & BLK_MQ_F_HOST_TAGS)
+		hctx = blk_mq_master_hctx(hctx);
+	atomic_dec(&hctx->nr_active);
+}
+
 static inline void blk_mq_put_dispatch_budget(struct blk_mq_hw_ctx *hctx)
 {
 	struct request_queue *q = hctx->queue;
@@ -218,7 +232,7 @@ static inline void __blk_mq_put_driver_tag(struct blk_mq_hw_ctx *hctx,
 
 	if (rq->rq_flags & RQF_MQ_INFLIGHT) {
 		rq->rq_flags &= ~RQF_MQ_INFLIGHT;
-		atomic_dec(&hctx->nr_active);
+		blk_mq_dec_nr_active(hctx);
 	}
 }
 
Thanks,
Ming