X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=block%2Fblk-flush.c;h=93d5fd8e51ebfe1126746321af3a9f143831ac83;hb=bed4ab7781e8600a7ebf4378a1b3f26d31517f57;hp=b27d0208611b4d904e7fda9e4e66bd9a4c7411b4;hpb=27b92d4ff2be2359a21ff4acde5b63563ff720e2;p=pandora-kernel.git diff --git a/block/blk-flush.c b/block/blk-flush.c index b27d0208611b..93d5fd8e51eb 100644 --- a/block/blk-flush.c +++ b/block/blk-flush.c @@ -1,6 +1,69 @@ /* * Functions to sequence FLUSH and FUA writes. + * + * Copyright (C) 2011 Max Planck Institute for Gravitational Physics + * Copyright (C) 2011 Tejun Heo + * + * This file is released under the GPLv2. + * + * REQ_{FLUSH|FUA} requests are decomposed to sequences consisted of three + * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request + * properties and hardware capability. + * + * If a request doesn't have data, only REQ_FLUSH makes sense, which + * indicates a simple flush request. If there is data, REQ_FLUSH indicates + * that the device cache should be flushed before the data is executed, and + * REQ_FUA means that the data must be on non-volatile media on request + * completion. + * + * If the device doesn't have writeback cache, FLUSH and FUA don't make any + * difference. The requests are either completed immediately if there's no + * data or executed as normal requests otherwise. + * + * If the device has writeback cache and supports FUA, REQ_FLUSH is + * translated to PREFLUSH but REQ_FUA is passed down directly with DATA. + * + * If the device has writeback cache and doesn't support FUA, REQ_FLUSH is + * translated to PREFLUSH and REQ_FUA to POSTFLUSH. + * + * The actual execution of flush is double buffered. Whenever a request + * needs to execute PRE or POSTFLUSH, it queues at + * q->flush_queue[q->flush_pending_idx]. Once certain criteria are met, a + * flush is issued and the pending_idx is toggled. When the flush + * completes, all the requests which were pending are proceeded to the next + * step. This allows arbitrary merging of different types of FLUSH/FUA + * requests. + * + * Currently, the following conditions are used to determine when to issue + * flush. + * + * C1. At any given time, only one flush shall be in progress. This makes + * double buffering sufficient. + * + * C2. Flush is deferred if any request is executing DATA of its sequence. + * This avoids issuing separate POSTFLUSHes for requests which shared + * PREFLUSH. + * + * C3. The second condition is ignored if there is a request which has + * waited longer than FLUSH_PENDING_TIMEOUT. This is to avoid + * starvation in the unlikely case where there are continuous stream of + * FUA (without FLUSH) requests. + * + * For devices which support FUA, it isn't clear whether C2 (and thus C3) + * is beneficial. + * + * Note that a sequenced FLUSH/FUA request with DATA is completed twice. + * Once while executing DATA and again after the whole sequence is + * complete. The first completion updates the contained bio but doesn't + * finish it so that the bio submitter is notified only after the whole + * sequence is complete. This is implemented by testing REQ_FLUSH_SEQ in + * req_bio_endio(). + * + * The above peculiarity requires that each FLUSH/FUA request has only one + * bio attached to it, which is guaranteed as they aren't allowed to be + * merged in the usual way. */ + #include #include #include @@ -11,58 +74,142 @@ /* FLUSH/FUA sequences */ enum { - QUEUE_FSEQ_STARTED = (1 << 0), /* flushing in progress */ - QUEUE_FSEQ_PREFLUSH = (1 << 1), /* pre-flushing in progress */ - QUEUE_FSEQ_DATA = (1 << 2), /* data write in progress */ - QUEUE_FSEQ_POSTFLUSH = (1 << 3), /* post-flushing in progress */ - QUEUE_FSEQ_DONE = (1 << 4), + REQ_FSEQ_PREFLUSH = (1 << 0), /* pre-flushing in progress */ + REQ_FSEQ_DATA = (1 << 1), /* data write in progress */ + REQ_FSEQ_POSTFLUSH = (1 << 2), /* post-flushing in progress */ + REQ_FSEQ_DONE = (1 << 3), + + REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA | + REQ_FSEQ_POSTFLUSH, + + /* + * If flush has been pending longer than the following timeout, + * it's issued even if flush_data requests are still in flight. + */ + FLUSH_PENDING_TIMEOUT = 5 * HZ, }; -static struct request *queue_next_fseq(struct request_queue *q); +static bool blk_kick_flush(struct request_queue *q); -unsigned blk_flush_cur_seq(struct request_queue *q) +static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq) { - if (!q->flush_seq) - return 0; - return 1 << ffz(q->flush_seq); + unsigned int policy = 0; + + if (fflags & REQ_FLUSH) { + if (rq->cmd_flags & REQ_FLUSH) + policy |= REQ_FSEQ_PREFLUSH; + if (blk_rq_sectors(rq)) + policy |= REQ_FSEQ_DATA; + if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA)) + policy |= REQ_FSEQ_POSTFLUSH; + } + return policy; } -static struct request *blk_flush_complete_seq(struct request_queue *q, - unsigned seq, int error) +static unsigned int blk_flush_cur_seq(struct request *rq) { - struct request *next_rq = NULL; - - if (error && !q->flush_err) - q->flush_err = error; - - BUG_ON(q->flush_seq & seq); - q->flush_seq |= seq; - - if (blk_flush_cur_seq(q) != QUEUE_FSEQ_DONE) { - /* not complete yet, queue the next flush sequence */ - next_rq = queue_next_fseq(q); - } else { - /* complete this flush request */ - __blk_end_request_all(q->orig_flush_rq, q->flush_err); - q->orig_flush_rq = NULL; - q->flush_seq = 0; - - /* dispatch the next flush if there's one */ - if (!list_empty(&q->pending_flushes)) { - next_rq = list_entry_rq(q->pending_flushes.next); - list_move(&next_rq->queuelist, &q->queue_head); - } + return 1 << ffz(rq->flush.seq); +} + +static void blk_flush_restore_request(struct request *rq) +{ + /* + * After flush data completion, @rq->bio is %NULL but we need to + * complete the bio again. @rq->biotail is guaranteed to equal the + * original @rq->bio. Restore it. + */ + rq->bio = rq->biotail; + + /* make @rq a normal request */ + rq->cmd_flags &= ~REQ_FLUSH_SEQ; + rq->end_io = NULL; +} + +/** + * blk_flush_complete_seq - complete flush sequence + * @rq: FLUSH/FUA request being sequenced + * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero) + * @error: whether an error occurred + * + * @rq just completed @seq part of its flush sequence, record the + * completion and trigger the next step. + * + * CONTEXT: + * spin_lock_irq(q->queue_lock) + * + * RETURNS: + * %true if requests were added to the dispatch queue, %false otherwise. + */ +static bool blk_flush_complete_seq(struct request *rq, unsigned int seq, + int error) +{ + struct request_queue *q = rq->q; + struct list_head *pending = &q->flush_queue[q->flush_pending_idx]; + bool queued = false; + + BUG_ON(rq->flush.seq & seq); + rq->flush.seq |= seq; + + if (likely(!error)) + seq = blk_flush_cur_seq(rq); + else + seq = REQ_FSEQ_DONE; + + switch (seq) { + case REQ_FSEQ_PREFLUSH: + case REQ_FSEQ_POSTFLUSH: + /* queue for flush */ + if (list_empty(pending)) + q->flush_pending_since = jiffies; + list_move_tail(&rq->flush.list, pending); + break; + + case REQ_FSEQ_DATA: + list_move_tail(&rq->flush.list, &q->flush_data_in_flight); + list_add(&rq->queuelist, &q->queue_head); + queued = true; + break; + + case REQ_FSEQ_DONE: + /* + * @rq was previously adjusted by blk_flush_issue() for + * flush sequencing and may already have gone through the + * flush data request completion path. Restore @rq for + * normal completion and end it. + */ + BUG_ON(!list_empty(&rq->queuelist)); + list_del_init(&rq->flush.list); + blk_flush_restore_request(rq); + __blk_end_request_all(rq, error); + break; + + default: + BUG(); } - return next_rq; + + return blk_kick_flush(q) | queued; } -static void blk_flush_complete_seq_end_io(struct request_queue *q, - unsigned seq, int error) +static void flush_end_io(struct request *flush_rq, int error) { - bool was_empty = elv_queue_empty(q); - struct request *next_rq; + struct request_queue *q = flush_rq->q; + struct list_head *running = &q->flush_queue[q->flush_running_idx]; + bool queued = false; + struct request *rq, *n; - next_rq = blk_flush_complete_seq(q, seq, error); + BUG_ON(q->flush_pending_idx == q->flush_running_idx); + + /* account completion of the flush request */ + q->flush_running_idx ^= 1; + elv_completed_request(q, flush_rq); + + /* and push the waiting requests to the next stage */ + list_for_each_entry_safe(rq, n, running, flush.list) { + unsigned int seq = blk_flush_cur_seq(rq); + + BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH); + queued |= blk_flush_complete_seq(rq, seq, error); + } /* * Moving a request silently to empty queue_head may stall the @@ -70,127 +217,153 @@ static void blk_flush_complete_seq_end_io(struct request_queue *q, * from request completion path and calling directly into * request_fn may confuse the driver. Always use kblockd. */ - if (was_empty && next_rq) + if (queued) __blk_run_queue(q, true); } -static void pre_flush_end_io(struct request *rq, int error) +/** + * blk_kick_flush - consider issuing flush request + * @q: request_queue being kicked + * + * Flush related states of @q have changed, consider issuing flush request. + * Please read the comment at the top of this file for more info. + * + * CONTEXT: + * spin_lock_irq(q->queue_lock) + * + * RETURNS: + * %true if flush was issued, %false otherwise. + */ +static bool blk_kick_flush(struct request_queue *q) { - elv_completed_request(rq->q, rq); - blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_PREFLUSH, error); + struct list_head *pending = &q->flush_queue[q->flush_pending_idx]; + struct request *first_rq = + list_first_entry(pending, struct request, flush.list); + + /* C1 described at the top of this file */ + if (q->flush_pending_idx != q->flush_running_idx || list_empty(pending)) + return false; + + /* C2 and C3 */ + if (!list_empty(&q->flush_data_in_flight) && + time_before(jiffies, + q->flush_pending_since + FLUSH_PENDING_TIMEOUT)) + return false; + + /* + * Issue flush and toggle pending_idx. This makes pending_idx + * different from running_idx, which means flush is in flight. + */ + blk_rq_init(q, &q->flush_rq); + q->flush_rq.cmd_type = REQ_TYPE_FS; + q->flush_rq.cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ; + q->flush_rq.rq_disk = first_rq->rq_disk; + q->flush_rq.end_io = flush_end_io; + + q->flush_pending_idx ^= 1; + elv_insert(q, &q->flush_rq, ELEVATOR_INSERT_REQUEUE); + return true; } static void flush_data_end_io(struct request *rq, int error) { - elv_completed_request(rq->q, rq); - blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_DATA, error); -} + struct request_queue *q = rq->q; -static void post_flush_end_io(struct request *rq, int error) -{ - elv_completed_request(rq->q, rq); - blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_POSTFLUSH, error); + /* + * After populating an empty queue, kick it to avoid stall. Read + * the comment in flush_end_io(). + */ + if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error)) + __blk_run_queue(q, true); } -static void init_flush_request(struct request *rq, struct gendisk *disk) +/** + * blk_insert_flush - insert a new FLUSH/FUA request + * @rq: request to insert + * + * To be called from elv_insert() for %ELEVATOR_INSERT_FLUSH insertions. + * @rq is being submitted. Analyze what needs to be done and put it on the + * right queue. + * + * CONTEXT: + * spin_lock_irq(q->queue_lock) + */ +void blk_insert_flush(struct request *rq) { - rq->cmd_type = REQ_TYPE_FS; - rq->cmd_flags = WRITE_FLUSH; - rq->rq_disk = disk; -} + struct request_queue *q = rq->q; + unsigned int fflags = q->flush_flags; /* may change, cache */ + unsigned int policy = blk_flush_policy(fflags, rq); -static struct request *queue_next_fseq(struct request_queue *q) -{ - struct request *orig_rq = q->orig_flush_rq; - struct request *rq = &q->flush_rq; + BUG_ON(rq->end_io); + BUG_ON(!rq->bio || rq->bio != rq->biotail); - blk_rq_init(q, rq); + /* + * @policy now records what operations need to be done. Adjust + * REQ_FLUSH and FUA for the driver. + */ + rq->cmd_flags &= ~REQ_FLUSH; + if (!(fflags & REQ_FUA)) + rq->cmd_flags &= ~REQ_FUA; - switch (blk_flush_cur_seq(q)) { - case QUEUE_FSEQ_PREFLUSH: - init_flush_request(rq, orig_rq->rq_disk); - rq->end_io = pre_flush_end_io; - break; - case QUEUE_FSEQ_DATA: - init_request_from_bio(rq, orig_rq->bio); - /* - * orig_rq->rq_disk may be different from - * bio->bi_bdev->bd_disk if orig_rq got here through - * remapping drivers. Make sure rq->rq_disk points - * to the same one as orig_rq. - */ - rq->rq_disk = orig_rq->rq_disk; - rq->cmd_flags &= ~(REQ_FLUSH | REQ_FUA); - rq->cmd_flags |= orig_rq->cmd_flags & (REQ_FLUSH | REQ_FUA); - rq->end_io = flush_data_end_io; - break; - case QUEUE_FSEQ_POSTFLUSH: - init_flush_request(rq, orig_rq->rq_disk); - rq->end_io = post_flush_end_io; - break; - default: - BUG(); + /* + * If there's data but flush is not necessary, the request can be + * processed directly without going through flush machinery. Queue + * for normal execution. + */ + if ((policy & REQ_FSEQ_DATA) && + !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) { + list_add(&rq->queuelist, &q->queue_head); + return; } - elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE); - return rq; + /* + * @rq should go through flush machinery. Mark it part of flush + * sequence and submit for further processing. + */ + memset(&rq->flush, 0, sizeof(rq->flush)); + INIT_LIST_HEAD(&rq->flush.list); + rq->cmd_flags |= REQ_FLUSH_SEQ; + rq->end_io = flush_data_end_io; + + blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0); } -struct request *blk_do_flush(struct request_queue *q, struct request *rq) +/** + * blk_abort_flushes - @q is being aborted, abort flush requests + * @q: request_queue being aborted + * + * To be called from elv_abort_queue(). @q is being aborted. Prepare all + * FLUSH/FUA requests for abortion. + * + * CONTEXT: + * spin_lock_irq(q->queue_lock) + */ +void blk_abort_flushes(struct request_queue *q) { - unsigned int fflags = q->flush_flags; /* may change, cache it */ - bool has_flush = fflags & REQ_FLUSH, has_fua = fflags & REQ_FUA; - bool do_preflush = has_flush && (rq->cmd_flags & REQ_FLUSH); - bool do_postflush = has_flush && !has_fua && (rq->cmd_flags & REQ_FUA); - unsigned skip = 0; + struct request *rq, *n; + int i; /* - * Special case. If there's data but flush is not necessary, - * the request can be issued directly. - * - * Flush w/o data should be able to be issued directly too but - * currently some drivers assume that rq->bio contains - * non-zero data if it isn't NULL and empty FLUSH requests - * getting here usually have bio's without data. + * Requests in flight for data are already owned by the dispatch + * queue or the device driver. Just restore for normal completion. */ - if (blk_rq_sectors(rq) && !do_preflush && !do_postflush) { - rq->cmd_flags &= ~REQ_FLUSH; - if (!has_fua) - rq->cmd_flags &= ~REQ_FUA; - return rq; + list_for_each_entry_safe(rq, n, &q->flush_data_in_flight, flush.list) { + list_del_init(&rq->flush.list); + blk_flush_restore_request(rq); } /* - * Sequenced flushes can't be processed in parallel. If - * another one is already in progress, queue for later - * processing. + * We need to give away requests on flush queues. Restore for + * normal completion and put them on the dispatch queue. */ - if (q->flush_seq) { - list_move_tail(&rq->queuelist, &q->pending_flushes); - return NULL; + for (i = 0; i < ARRAY_SIZE(q->flush_queue); i++) { + list_for_each_entry_safe(rq, n, &q->flush_queue[i], + flush.list) { + list_del_init(&rq->flush.list); + blk_flush_restore_request(rq); + list_add_tail(&rq->queuelist, &q->queue_head); + } } - - /* - * Start a new flush sequence - */ - q->flush_err = 0; - q->flush_seq |= QUEUE_FSEQ_STARTED; - - /* adjust FLUSH/FUA of the original request and stash it away */ - rq->cmd_flags &= ~REQ_FLUSH; - if (!has_fua) - rq->cmd_flags &= ~REQ_FUA; - blk_dequeue_request(rq); - q->orig_flush_rq = rq; - - /* skip unneded sequences and return the first one */ - if (!do_preflush) - skip |= QUEUE_FSEQ_PREFLUSH; - if (!blk_rq_sectors(rq)) - skip |= QUEUE_FSEQ_DATA; - if (!do_postflush) - skip |= QUEUE_FSEQ_POSTFLUSH; - return blk_flush_complete_seq(q, skip, 0); } static void bio_end_flush(struct bio *bio, int err)