diff options
| -rw-r--r-- | block/bfq-iosched.c | 107 |
1 files changed, 82 insertions, 25 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 47e6ec7427c4..aeca22d91101 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -3823,24 +3823,26 @@ static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx) } /* - * We exploit the bfq_finish_request hook to decrement - * rq_in_driver, but bfq_finish_request will not be - * invoked on this request. So, to avoid unbalance, - * just start this request, without incrementing - * rq_in_driver. As a negative consequence, - * rq_in_driver is deceptively lower than it should be - * while this request is in service. This may cause - * bfq_schedule_dispatch to be invoked uselessly. + * We exploit the bfq_finish_requeue_request hook to + * decrement rq_in_driver, but + * bfq_finish_requeue_request will not be invoked on + * this request. So, to avoid unbalance, just start + * this request, without incrementing rq_in_driver. As + * a negative consequence, rq_in_driver is deceptively + * lower than it should be while this request is in + * service. This may cause bfq_schedule_dispatch to be + * invoked uselessly. * * As for implementing an exact solution, the - * bfq_finish_request hook, if defined, is probably - * invoked also on this request. So, by exploiting - * this hook, we could 1) increment rq_in_driver here, - * and 2) decrement it in bfq_finish_request. Such a - * solution would let the value of the counter be - * always accurate, but it would entail using an extra - * interface function. This cost seems higher than the - * benefit, being the frequency of non-elevator-private + * bfq_finish_requeue_request hook, if defined, is + * probably invoked also on this request. So, by + * exploiting this hook, we could 1) increment + * rq_in_driver here, and 2) decrement it in + * bfq_finish_requeue_request. Such a solution would + * let the value of the counter be always accurate, + * but it would entail using an extra interface + * function. This cost seems higher than the benefit, + * being the frequency of non-elevator-private * requests very low. */ goto start_rq; @@ -4515,6 +4517,8 @@ static inline void bfq_update_insert_stats(struct request_queue *q, unsigned int cmd_flags) {} #endif +static void bfq_prepare_request(struct request *rq, struct bio *bio); + static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, bool at_head) { @@ -4541,6 +4545,18 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, else list_add_tail(&rq->queuelist, &bfqd->dispatch); } else { + if (WARN_ON_ONCE(!bfqq)) { + /* + * This should never happen. Most likely rq is + * a requeued regular request, being + * re-inserted without being first + * re-prepared. Do a prepare, to avoid + * failure. + */ + bfq_prepare_request(rq, rq->bio); + bfqq = RQ_BFQQ(rq); + } + idle_timer_disabled = __bfq_insert_request(bfqd, rq); /* * Update bfqq, because, if a queue merge has occurred @@ -4697,22 +4713,44 @@ static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd) bfq_schedule_dispatch(bfqd); } -static void bfq_finish_request_body(struct bfq_queue *bfqq) +static void bfq_finish_requeue_request_body(struct bfq_queue *bfqq) { bfqq->allocated--; bfq_put_queue(bfqq); } -static void bfq_finish_request(struct request *rq) +/* + * Handle either a requeue or a finish for rq. The things to do are + * the same in both cases: all references to rq are to be dropped. In + * particular, rq is considered completed from the point of view of + * the scheduler. + */ +static void bfq_finish_requeue_request(struct request *rq) { - struct bfq_queue *bfqq; + struct bfq_queue *bfqq = RQ_BFQQ(rq); struct bfq_data *bfqd; - if (!rq->elv.icq) + /* + * Requeue and finish hooks are invoked in blk-mq without + * checking whether the involved request is actually still + * referenced in the scheduler. To handle this fact, the + * following two checks make this function exit in case of + * spurious invocations, for which there is nothing to do. + * + * First, check whether rq has nothing to do with an elevator. + */ + if (unlikely(!(rq->rq_flags & RQF_ELVPRIV))) + return; + + /* + * rq either is not associated with any icq, or is an already + * requeued request that has not (yet) been re-inserted into + * a bfq_queue. + */ + if (!rq->elv.icq || !bfqq) return; - bfqq = RQ_BFQQ(rq); bfqd = bfqq->bfqd; if (rq->rq_flags & RQF_STARTED) @@ -4727,13 +4765,14 @@ static void bfq_finish_request(struct request *rq) spin_lock_irqsave(&bfqd->lock, flags); bfq_completed_request(bfqq, bfqd); - bfq_finish_request_body(bfqq); + bfq_finish_requeue_request_body(bfqq); spin_unlock_irqrestore(&bfqd->lock, flags); } else { /* * Request rq may be still/already in the scheduler, - * in which case we need to remove it. And we cannot + * in which case we need to remove it (this should + * never happen in case of requeue). And we cannot * defer such a check and removal, to avoid * inconsistencies in the time interval from the end * of this function to the start of the deferred work. @@ -4748,9 +4787,26 @@ static void bfq_finish_request(struct request *rq) bfqg_stats_update_io_remove(bfqq_group(bfqq), rq->cmd_flags); } - bfq_finish_request_body(bfqq); + bfq_finish_requeue_request_body(bfqq); } + /* + * Reset private fields. In case of a requeue, this allows + * this function to correctly do nothing if it is spuriously + * invoked again on this same request (see the check at the + * beginning of the function). Probably, a better general + * design would be to prevent blk-mq from invoking the requeue + * or finish hooks of an elevator, for a request that is not + * referred by that elevator. + * + * Resetting the following fields would break the + * request-insertion logic if rq is re-inserted into a bfq + * internal queue, without a re-preparation. Here we assume + * that re-insertions of requeued requests, without + * re-preparation, can happen only for pass_through or at_head + * requests (which are not re-inserted into bfq internal + * queues). + */ rq->elv.priv[0] = NULL; rq->elv.priv[1] = NULL; } @@ -5426,7 +5482,8 @@ static struct elevator_type iosched_bfq_mq = { .ops.mq = { .limit_depth = bfq_limit_depth, .prepare_request = bfq_prepare_request, - .finish_request = bfq_finish_request, + .requeue_request = bfq_finish_requeue_request, + .finish_request = bfq_finish_requeue_request, .exit_icq = bfq_exit_icq, .insert_requests = bfq_insert_requests, .dispatch_request = bfq_dispatch_request, |