/*
* Functions to sequence FLUSH and FUA writes.
+ *
+ * Copyright (C) 2011 Max Planck Institute for Gravitational Physics
+ * Copyright (C) 2011 Tejun Heo <tj@kernel.org>
+ *
+ * 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 <linux/kernel.h>
#include <linux/module.h>
#include <linux/bio.h>
/* 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)
{
+ struct request_queue *q = flush_rq->q;
+ struct list_head *running = &q->flush_queue[q->flush_running_idx];
bool was_empty = elv_queue_empty(q);
- struct request *next_rq;
+ bool queued = false;
+ struct request *rq, *n;
+
+ 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);
- next_rq = blk_flush_complete_seq(q, seq, error);
+ 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
* from request completion path and calling directly into
* request_fn may confuse the driver. Always use kblockd.
*/
- if (was_empty && next_rq)
+ if (queued && was_empty)
__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;
+ bool was_empty = elv_queue_empty(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) && was_empty)
+ __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)
git.openpandora.org / pandora-kernel.git / blobdiff