On Wed, May 12, 2021 at 12:15:43AM +0800, John Garry wrote: > The tags used for an IO scheduler are currently per hctx. > > As such, when q->nr_hw_queues grows, so does the request queue total IO > scheduler tag depth. > > This may cause problems for SCSI MQ HBAs whose total driver depth is > fixed. > > Ming and Yanhui report higher CPU usage and lower throughput in scenarios > where the fixed total driver tag depth is appreciably lower than the total > scheduler tag depth: > https://lore.kernel.org/linux-block/440dfcfc-1a2c-bd98-1161-cec4d78c6dfc@xxxxxxxxxx/T/#mc0d6d4f95275a2743d1c8c3e4dc9ff6c9aa3a76b > > In that scenario, since the scheduler tag is got first, much contention > is introduced since a driver tag may not be available after we have got > the sched tag. > > Improve this scenario by introducing request queue-wide tags for when > a tagset-wide sbitmap is used. The static sched requests are still > allocated per hctx, as requests are initialised per hctx, as in > blk_mq_init_request(..., hctx_idx, ...) -> > set->ops->init_request(.., hctx_idx, ...). > > For simplicity of resizing the request queue sbitmap when updating the > request queue depth, just init at the max possible size, so we don't need > to deal with the possibly with swapping out a new sbitmap for old if > we need to grow. > > Signed-off-by: John Garry <john.garry@xxxxxxxxxx> > --- > > Please retest, thanks! For some reason I could not recreate the original > issue, but I am using qemu... > > Changes since v1: > - Embed sbitmaps in request_queue struct > - Relocate IO sched functions to blk-mq-sched.c > - Fix error path code > > diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c > index 42a365b1b9c0..9a012e0818cb 100644 > --- a/block/blk-mq-sched.c > +++ b/block/blk-mq-sched.c > @@ -507,11 +507,9 @@ static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set, > struct blk_mq_hw_ctx *hctx, > unsigned int hctx_idx) > { > - unsigned int flags = set->flags & ~BLK_MQ_F_TAG_HCTX_SHARED; > - > if (hctx->sched_tags) { > blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx); > - blk_mq_free_rq_map(hctx->sched_tags, flags); > + blk_mq_free_rq_map(hctx->sched_tags, set->flags); > hctx->sched_tags = NULL; > } > } > @@ -521,12 +519,10 @@ static int blk_mq_sched_alloc_tags(struct request_queue *q, > unsigned int hctx_idx) > { > struct blk_mq_tag_set *set = q->tag_set; > - /* Clear HCTX_SHARED so tags are init'ed */ > - unsigned int flags = set->flags & ~BLK_MQ_F_TAG_HCTX_SHARED; > int ret; > > hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests, > - set->reserved_tags, flags); > + set->reserved_tags, set->flags); > if (!hctx->sched_tags) > return -ENOMEM; > > @@ -544,16 +540,40 @@ static void blk_mq_sched_tags_teardown(struct request_queue *q) > int i; > > queue_for_each_hw_ctx(q, hctx, i) { > - /* Clear HCTX_SHARED so tags are freed */ > - unsigned int flags = hctx->flags & ~BLK_MQ_F_TAG_HCTX_SHARED; > - > if (hctx->sched_tags) { > - blk_mq_free_rq_map(hctx->sched_tags, flags); > + blk_mq_free_rq_map(hctx->sched_tags, hctx->flags); > hctx->sched_tags = NULL; > } > } > } > > +static int blk_mq_init_sched_shared_sbitmap(struct request_queue *queue) > +{ > + struct blk_mq_tag_set *set = queue->tag_set; > + int ret; > + > + /* > + * Set initial depth at max so that we don't need to reallocate for > + * updating nr_requests. > + */ > + ret = blk_mq_init_bitmaps(&queue->sched_bitmap_tags, > + &queue->sched_breserved_tags, > + set, MAX_SCHED_RQ, set->reserved_tags); > + if (ret) > + return ret; > + > + sbitmap_queue_resize(&queue->sched_bitmap_tags, > + queue->nr_requests - set->reserved_tags); > + > + return 0; > +} > + > +static void blk_mq_exit_sched_shared_sbitmap(struct request_queue *queue) > +{ > + sbitmap_queue_free(&queue->sched_bitmap_tags); > + sbitmap_queue_free(&queue->sched_breserved_tags); > +} > + > int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e) > { > struct blk_mq_hw_ctx *hctx; > @@ -578,12 +598,25 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e) > queue_for_each_hw_ctx(q, hctx, i) { > ret = blk_mq_sched_alloc_tags(q, hctx, i); > if (ret) > - goto err; > + goto err_free_tags; > + } > + > + if (blk_mq_is_sbitmap_shared(q->tag_set->flags)) { > + ret = blk_mq_init_sched_shared_sbitmap(q); > + if (ret) > + goto err_free_tags; > + > + queue_for_each_hw_ctx(q, hctx, i) { > + hctx->sched_tags->bitmap_tags = > + &q->sched_bitmap_tags; > + hctx->sched_tags->breserved_tags = > + &q->sched_breserved_tags; > + } The above assignment can be folded into blk_mq_init_sched_shared_sbitmap(). > } > > ret = e->ops.init_sched(q, e); > if (ret) > - goto err; > + goto err_free_sbitmap; > > blk_mq_debugfs_register_sched(q); > > @@ -603,7 +636,10 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e) > > return 0; > > -err: > +err_free_sbitmap: > + if (blk_mq_is_sbitmap_shared(q->tag_set->flags)) > + blk_mq_exit_sched_shared_sbitmap(q); > +err_free_tags: > blk_mq_sched_free_requests(q); > blk_mq_sched_tags_teardown(q); > q->elevator = NULL; > @@ -641,5 +677,7 @@ void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e) > if (e->type->ops.exit_sched) > e->type->ops.exit_sched(e); > blk_mq_sched_tags_teardown(q); > + if (blk_mq_is_sbitmap_shared(q->tag_set->flags)) > + blk_mq_exit_sched_shared_sbitmap(q); The above two lines can be moved to blk_mq_sched_tags_teardown(). > q->elevator = NULL; > } > diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h > index 5b18ab915c65..aff037cfd8e7 100644 > --- a/block/blk-mq-sched.h > +++ b/block/blk-mq-sched.h > @@ -5,6 +5,8 @@ > #include "blk-mq.h" > #include "blk-mq-tag.h" > > +#define MAX_SCHED_RQ (16 * BLKDEV_MAX_RQ) > + > void blk_mq_sched_assign_ioc(struct request *rq); > > bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio, > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c > index 2a37731e8244..e3ab8631be22 100644 > --- a/block/blk-mq-tag.c > +++ b/block/blk-mq-tag.c > @@ -13,6 +13,7 @@ > #include <linux/delay.h> > #include "blk.h" > #include "blk-mq.h" > +#include "blk-mq-sched.h" > #include "blk-mq-tag.h" > > /* > @@ -466,19 +467,39 @@ static int blk_mq_init_bitmap_tags(struct blk_mq_tags *tags, > return -ENOMEM; > } > > -int blk_mq_init_shared_sbitmap(struct blk_mq_tag_set *set, unsigned int flags) > +int blk_mq_init_bitmaps(struct sbitmap_queue *bitmap_tags, > + struct sbitmap_queue *breserved_tags, > + struct blk_mq_tag_set *set, The 'set' parameter can be killed, meantime pass 'node' & 'alloc_policy', just like blk_mq_init_bitmap_tags()'s type, then blk_mq_init_bitmaps() can be re-used by blk_mq_init_bitmap_tags() for avoiding to duplicate bitmap allocation code. > + unsigned int queue_depth, unsigned int reserved) > { > - unsigned int depth = set->queue_depth - set->reserved_tags; > + unsigned int depth = queue_depth - reserved; > int alloc_policy = BLK_MQ_FLAG_TO_ALLOC_POLICY(set->flags); > bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR; > - int i, node = set->numa_node; > > - if (bt_alloc(&set->__bitmap_tags, depth, round_robin, node)) > + if (bt_alloc(bitmap_tags, depth, round_robin, set->numa_node)) > return -ENOMEM; > - if (bt_alloc(&set->__breserved_tags, set->reserved_tags, > - round_robin, node)) > + if (bt_alloc(breserved_tags, set->reserved_tags, s/set->reserved_tags/reserved/ Thanks, Ming
