diff options
| -rw-r--r-- | block/blk-throttle.c | 201 |
1 files changed, 176 insertions, 25 deletions
diff --git a/block/blk-throttle.c b/block/blk-throttle.c index bc65077f6e4..541bd0dabb9 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -26,6 +26,35 @@ static struct blkcg_policy blkcg_policy_throtl; /* A workqueue to queue throttle related work */ static struct workqueue_struct *kthrotld_workqueue; +/* + * To implement hierarchical throttling, throtl_grps form a tree and bios + * are dispatched upwards level by level until they reach the top and get + * issued. When dispatching bios from the children and local group at each + * level, if the bios are dispatched into a single bio_list, there's a risk + * of a local or child group which can queue many bios at once filling up + * the list starving others. + * + * To avoid such starvation, dispatched bios are queued separately + * according to where they came from. When they are again dispatched to + * the parent, they're popped in round-robin order so that no single source + * hogs the dispatch window. + * + * throtl_qnode is used to keep the queued bios separated by their sources. + * Bios are queued to throtl_qnode which in turn is queued to + * throtl_service_queue and then dispatched in round-robin order. + * + * It's also used to track the reference counts on blkg's. A qnode always + * belongs to a throtl_grp and gets queued on itself or the parent, so + * incrementing the reference of the associated throtl_grp when a qnode is + * queued and decrementing when dequeued is enough to keep the whole blkg + * tree pinned while bios are in flight. + */ +struct throtl_qnode { + struct list_head node; /* service_queue->queued[] */ + struct bio_list bios; /* queued bios */ + struct throtl_grp *tg; /* tg this qnode belongs to */ +}; + struct throtl_service_queue { struct throtl_service_queue *parent_sq; /* the parent service_queue */ @@ -33,7 +62,7 @@ struct throtl_service_queue { * Bios queued directly to this service_queue or dispatched from * children throtl_grp's. */ - struct bio_list bio_lists[2]; /* queued bios [READ/WRITE] */ + struct list_head queued[2]; /* throtl_qnode [READ/WRITE] */ unsigned int nr_queued[2]; /* number of queued bios */ /* @@ -76,6 +105,17 @@ struct throtl_grp { struct throtl_service_queue service_queue; /* + * qnode_on_self is used when bios are directly queued to this + * throtl_grp so that local bios compete fairly with bios + * dispatched from children. qnode_on_parent is used when bios are + * dispatched from this throtl_grp into its parent and will compete + * with the sibling qnode_on_parents and the parent's + * qnode_on_self. + */ + struct throtl_qnode qnode_on_self[2]; + struct throtl_qnode qnode_on_parent[2]; + + /* * Dispatch time in jiffies. This is the estimated time when group * will unthrottle and is ready to dispatch more bio. It is used as * key to sort active groups in service tree. @@ -250,12 +290,95 @@ alloc_stats: goto alloc_stats; } +static void throtl_qnode_init(struct throtl_qnode *qn, struct throtl_grp *tg) +{ + INIT_LIST_HEAD(&qn->node); + bio_list_init(&qn->bios); + qn->tg = tg; +} + +/** + * throtl_qnode_add_bio - add a bio to a throtl_qnode and activate it + * @bio: bio being added + * @qn: qnode to add bio to + * @queued: the service_queue->queued[] list @qn belongs to + * + * Add @bio to @qn and put @qn on @queued if it's not already on. + * @qn->tg's reference count is bumped when @qn is activated. See the + * comment on top of throtl_qnode definition for details. + */ +static void throtl_qnode_add_bio(struct bio *bio, struct throtl_qnode *qn, + struct list_head *queued) +{ + bio_list_add(&qn->bios, bio); + if (list_empty(&qn->node)) { + list_add_tail(&qn->node, queued); + blkg_get(tg_to_blkg(qn->tg)); + } +} + +/** + * throtl_peek_queued - peek the first bio on a qnode list + * @queued: the qnode list to peek + */ +static struct bio *throtl_peek_queued(struct list_head *queued) +{ + struct throtl_qnode *qn = list_first_entry(queued, struct throtl_qnode, node); + struct bio *bio; + + if (list_empty(queued)) + return NULL; + + bio = bio_list_peek(&qn->bios); + WARN_ON_ONCE(!bio); + return bio; +} + +/** + * throtl_pop_queued - pop the first bio form a qnode list + * @queued: the qnode list to pop a bio from + * @tg_to_put: optional out argument for throtl_grp to put + * + * Pop the first bio from the qnode list @queued. After popping, the first + * qnode is removed from @queued if empty or moved to the end of @queued so + * that the popping order is round-robin. + * + * When the first qnode is removed, its associated throtl_grp should be put + * too. If @tg_to_put is NULL, this function automatically puts it; + * otherwise, *@tg_to_put is set to the throtl_grp to put and the caller is + * responsible for putting it. + */ +static struct bio *throtl_pop_queued(struct list_head *queued, + struct throtl_grp **tg_to_put) +{ + struct throtl_qnode *qn = list_first_entry(queued, struct throtl_qnode, node); + struct bio *bio; + + if (list_empty(queued)) + return NULL; + + bio = bio_list_pop(&qn->bios); + WARN_ON_ONCE(!bio); + + if (bio_list_empty(&qn->bios)) { + list_del_init(&qn->node); + if (tg_to_put) + *tg_to_put = qn->tg; + else + blkg_put(tg_to_blkg(qn->tg)); + } else { + list_move_tail(&qn->node, queued); + } + + return bio; +} + /* init a service_queue, assumes the caller zeroed it */ static void throtl_service_queue_init(struct throtl_service_queue *sq, struct throtl_service_queue *parent_sq) { - bio_list_init(&sq->bio_lists[0]); - bio_list_init(&sq->bio_lists[1]); + INIT_LIST_HEAD(&sq->queued[0]); + INIT_LIST_HEAD(&sq->queued[1]); sq->pending_tree = RB_ROOT; sq->parent_sq = parent_sq; setup_timer(&sq->pending_timer, throtl_pending_timer_fn, @@ -272,8 +395,14 @@ static void throtl_pd_init(struct blkcg_gq *blkg) struct throtl_grp *tg = blkg_to_tg(blkg); struct throtl_data *td = blkg->q->td; unsigned long flags; + int rw; throtl_service_queue_init(&tg->service_queue, &td->service_queue); + for (rw = READ; rw <= WRITE; rw++) { + throtl_qnode_init(&tg->qnode_on_self[rw], tg); + throtl_qnode_init(&tg->qnode_on_parent[rw], tg); + } + RB_CLEAR_NODE(&tg->rb_node); tg->td = td; @@ -715,7 +844,7 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio, * queued. */ BUG_ON(tg->service_queue.nr_queued[rw] && - bio != bio_list_peek(&tg->service_queue.bio_lists[rw])); + bio != throtl_peek_queued(&tg->service_queue.queued[rw])); /* If tg->bps = -1, then BW is unlimited */ if (tg->bps[rw] == -1 && tg->iops[rw] == -1) { @@ -806,11 +935,24 @@ static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio) } } -static void throtl_add_bio_tg(struct bio *bio, struct throtl_grp *tg) +/** + * throtl_add_bio_tg - add a bio to the specified throtl_grp + * @bio: bio to add + * @qn: qnode to use + * @tg: the target throtl_grp + * + * Add @bio to @tg's service_queue using @qn. If @qn is not specified, + * tg->qnode_on_self[] is used. + */ +static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn, + struct throtl_grp *tg) { struct throtl_service_queue *sq = &tg->service_queue; bool rw = bio_data_dir(bio); + if (!qn) + qn = &tg->qnode_on_self[rw]; + /* * If @tg doesn't currently have any bios queued in the same * direction, queueing @bio can change when @tg should be @@ -820,9 +962,8 @@ static void throtl_add_bio_tg(struct bio *bio, struct throtl_grp *tg) if (!sq->nr_queued[rw]) tg->flags |= THROTL_TG_WAS_EMPTY; - bio_list_add(&sq->bio_lists[rw], bio); - /* Take a bio reference on tg */ - blkg_get(tg_to_blkg(tg)); + throtl_qnode_add_bio(bio, qn, &sq->queued[rw]); + sq->nr_queued[rw]++; throtl_enqueue_tg(tg); } @@ -833,10 +974,10 @@ static void tg_update_disptime(struct throtl_grp *tg) unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime; struct bio *bio; - if ((bio = bio_list_peek(&sq->bio_lists[READ]))) + if ((bio = throtl_peek_queued(&sq->queued[READ]))) tg_may_dispatch(tg, bio, &read_wait); - if ((bio = bio_list_peek(&sq->bio_lists[WRITE]))) + if ((bio = throtl_peek_queued(&sq->queued[WRITE]))) tg_may_dispatch(tg, bio, &write_wait); min_wait = min(read_wait, write_wait); @@ -856,9 +997,16 @@ static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw) struct throtl_service_queue *sq = &tg->service_queue; struct throtl_service_queue *parent_sq = sq->parent_sq; struct throtl_grp *parent_tg = sq_to_tg(parent_sq); + struct throtl_grp *tg_to_put = NULL; struct bio *bio; - bio = bio_list_pop(&sq->bio_lists[rw]); + /* + * @bio is being transferred from @tg to @parent_sq. Popping a bio + * from @tg may put its reference and @parent_sq might end up + * getting released prematurely. Remember the tg to put and put it + * after @bio is transferred to @parent_sq. + */ + bio = throtl_pop_queued(&sq->queued[rw], &tg_to_put); sq->nr_queued[rw]--; throtl_charge_bio(tg, bio); @@ -871,17 +1019,18 @@ static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw) * responsible for issuing these bios. */ if (parent_tg) { - throtl_add_bio_tg(bio, parent_tg); + throtl_add_bio_tg(bio, &tg->qnode_on_parent[rw], parent_tg); } else { - bio_list_add(&parent_sq->bio_lists[rw], bio); + throtl_qnode_add_bio(bio, &tg->qnode_on_parent[rw], + &parent_sq->queued[rw]); BUG_ON(tg->td->nr_queued[rw] <= 0); tg->td->nr_queued[rw]--; } throtl_trim_slice(tg, rw); - /* @bio is transferred to parent, drop its blkg reference */ - blkg_put(tg_to_blkg(tg)); + if (tg_to_put) + blkg_put(tg_to_blkg(tg_to_put)); } static int throtl_dispatch_tg(struct throtl_grp *tg) @@ -894,7 +1043,7 @@ static int throtl_dispatch_tg(struct throtl_grp *tg) /* Try to dispatch 75% READS and 25% WRITES */ - while ((bio = bio_list_peek(&sq->bio_lists[READ])) && + while ((bio = throtl_peek_queued(&sq->queued[READ])) && tg_may_dispatch(tg, bio, NULL)) { tg_dispatch_one_bio(tg, bio_data_dir(bio)); @@ -904,7 +1053,7 @@ static int throtl_dispatch_tg(struct throtl_grp *tg) break; } - while ((bio = bio_list_peek(&sq->bio_lists[WRITE])) && + while ((bio = throtl_peek_queued(&sq->queued[WRITE])) && tg_may_dispatch(tg, bio, NULL)) { tg_dispatch_one_bio(tg, bio_data_dir(bio)); @@ -1039,10 +1188,9 @@ void blk_throtl_dispatch_work_fn(struct work_struct *work) bio_list_init(&bio_list_on_stack); spin_lock_irq(q->queue_lock); - for (rw = READ; rw <= WRITE; rw++) { - bio_list_merge(&bio_list_on_stack, &td_sq->bio_lists[rw]); - bio_list_init(&td_sq->bio_lists[rw]); - } + for (rw = READ; rw <= WRITE; rw++) + while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL))) + bio_list_add(&bio_list_on_stack, bio); spin_unlock_irq(q->queue_lock); if (!bio_list_empty(&bio_list_on_stack)) { @@ -1241,6 +1389,7 @@ static struct blkcg_policy blkcg_policy_throtl = { bool blk_throtl_bio(struct request_queue *q, struct bio *bio) { struct throtl_data *td = q->td; + struct throtl_qnode *qn = NULL; struct throtl_grp *tg; struct throtl_service_queue *sq; bool rw = bio_data_dir(bio); @@ -1308,6 +1457,7 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio) * Climb up the ladder. If we''re already at the top, it * can be executed directly. */ + qn = &tg->qnode_on_parent[rw]; sq = sq->parent_sq; tg = sq_to_tg(sq); if (!tg) @@ -1323,7 +1473,7 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio) bio_associate_current(bio); tg->td->nr_queued[rw]++; - throtl_add_bio_tg(bio, tg); + throtl_add_bio_tg(bio, qn, tg); throttled = true; /* @@ -1367,9 +1517,9 @@ static void tg_drain_bios(struct throtl_service_queue *parent_sq) throtl_dequeue_tg(tg); - while ((bio = bio_list_peek(&sq->bio_lists[READ]))) + while ((bio = throtl_peek_queued(&sq->queued[READ]))) tg_dispatch_one_bio(tg, bio_data_dir(bio)); - while ((bio = bio_list_peek(&sq->bio_lists[WRITE]))) + while ((bio = throtl_peek_queued(&sq->queued[WRITE]))) tg_dispatch_one_bio(tg, bio_data_dir(bio)); } } @@ -1411,7 +1561,8 @@ void blk_throtl_drain(struct request_queue *q) /* all bios now should be in td->service_queue, issue them */ for (rw = READ; rw <= WRITE; rw++) - while ((bio = bio_list_pop(&td->service_queue.bio_lists[rw]))) + while ((bio = throtl_pop_queued(&td->service_queue.queued[rw], + NULL))) generic_make_request(bio); spin_lock_irq(q->queue_lock); |