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authorJens Axboe <axboe@kernel.dk>2013-10-24 09:20:05 +0100
committerJens Axboe <axboe@kernel.dk>2013-10-25 11:56:00 +0100
commit320ae51feed5c2f13664aa05a76bec198967e04d (patch)
treead37ccbcc5ddb1c9c19e48965bf8fec1b05217dc /block/blk-flush.c
parent1dddc01af0d42b21058e0cb9c1ca9e8d5204d9b0 (diff)
downloadop-kernel-dev-320ae51feed5c2f13664aa05a76bec198967e04d.zip
op-kernel-dev-320ae51feed5c2f13664aa05a76bec198967e04d.tar.gz
blk-mq: new multi-queue block IO queueing mechanism
Linux currently has two models for block devices: - The classic request_fn based approach, where drivers use struct request units for IO. The block layer provides various helper functionalities to let drivers share code, things like tag management, timeout handling, queueing, etc. - The "stacked" approach, where a driver squeezes in between the block layer and IO submitter. Since this bypasses the IO stack, driver generally have to manage everything themselves. With drivers being written for new high IOPS devices, the classic request_fn based driver doesn't work well enough. The design dates back to when both SMP and high IOPS was rare. It has problems with scaling to bigger machines, and runs into scaling issues even on smaller machines when you have IOPS in the hundreds of thousands per device. The stacked approach is then most often selected as the model for the driver. But this means that everybody has to re-invent everything, and along with that we get all the problems again that the shared approach solved. This commit introduces blk-mq, block multi queue support. The design is centered around per-cpu queues for queueing IO, which then funnel down into x number of hardware submission queues. We might have a 1:1 mapping between the two, or it might be an N:M mapping. That all depends on what the hardware supports. blk-mq provides various helper functions, which include: - Scalable support for request tagging. Most devices need to be able to uniquely identify a request both in the driver and to the hardware. The tagging uses per-cpu caches for freed tags, to enable cache hot reuse. - Timeout handling without tracking request on a per-device basis. Basically the driver should be able to get a notification, if a request happens to fail. - Optional support for non 1:1 mappings between issue and submission queues. blk-mq can redirect IO completions to the desired location. - Support for per-request payloads. Drivers almost always need to associate a request structure with some driver private command structure. Drivers can tell blk-mq this at init time, and then any request handed to the driver will have the required size of memory associated with it. - Support for merging of IO, and plugging. The stacked model gets neither of these. Even for high IOPS devices, merging sequential IO reduces per-command overhead and thus increases bandwidth. For now, this is provided as a potential 3rd queueing model, with the hope being that, as it matures, it can replace both the classic and stacked model. That would get us back to having just 1 real model for block devices, leaving the stacked approach to dm/md devices (as it was originally intended). Contributions in this patch from the following people: Shaohua Li <shli@fusionio.com> Alexander Gordeev <agordeev@redhat.com> Christoph Hellwig <hch@infradead.org> Mike Christie <michaelc@cs.wisc.edu> Matias Bjorling <m@bjorling.me> Jeff Moyer <jmoyer@redhat.com> Acked-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-flush.c')
-rw-r--r--block/blk-flush.c154
1 files changed, 139 insertions, 15 deletions
diff --git a/block/blk-flush.c b/block/blk-flush.c
index cc2b827..3e4cc9c 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -69,8 +69,10 @@
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/gfp.h>
+#include <linux/blk-mq.h>
#include "blk.h"
+#include "blk-mq.h"
/* FLUSH/FUA sequences */
enum {
@@ -124,6 +126,24 @@ static void blk_flush_restore_request(struct request *rq)
/* make @rq a normal request */
rq->cmd_flags &= ~REQ_FLUSH_SEQ;
rq->end_io = rq->flush.saved_end_io;
+
+ blk_clear_rq_complete(rq);
+}
+
+static void mq_flush_data_run(struct work_struct *work)
+{
+ struct request *rq;
+
+ rq = container_of(work, struct request, mq_flush_data);
+
+ memset(&rq->csd, 0, sizeof(rq->csd));
+ blk_mq_run_request(rq, true, false);
+}
+
+static void blk_mq_flush_data_insert(struct request *rq)
+{
+ INIT_WORK(&rq->mq_flush_data, mq_flush_data_run);
+ kblockd_schedule_work(rq->q, &rq->mq_flush_data);
}
/**
@@ -136,7 +156,7 @@ static void blk_flush_restore_request(struct request *rq)
* completion and trigger the next step.
*
* CONTEXT:
- * spin_lock_irq(q->queue_lock)
+ * spin_lock_irq(q->queue_lock or q->mq_flush_lock)
*
* RETURNS:
* %true if requests were added to the dispatch queue, %false otherwise.
@@ -146,7 +166,7 @@ static bool blk_flush_complete_seq(struct request *rq, unsigned int seq,
{
struct request_queue *q = rq->q;
struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
- bool queued = false;
+ bool queued = false, kicked;
BUG_ON(rq->flush.seq & seq);
rq->flush.seq |= seq;
@@ -167,8 +187,12 @@ static bool blk_flush_complete_seq(struct request *rq, unsigned int seq,
case REQ_FSEQ_DATA:
list_move_tail(&rq->flush.list, &q->flush_data_in_flight);
- list_add(&rq->queuelist, &q->queue_head);
- queued = true;
+ if (q->mq_ops)
+ blk_mq_flush_data_insert(rq);
+ else {
+ list_add(&rq->queuelist, &q->queue_head);
+ queued = true;
+ }
break;
case REQ_FSEQ_DONE:
@@ -181,28 +205,43 @@ static bool blk_flush_complete_seq(struct request *rq, unsigned int seq,
BUG_ON(!list_empty(&rq->queuelist));
list_del_init(&rq->flush.list);
blk_flush_restore_request(rq);
- __blk_end_request_all(rq, error);
+ if (q->mq_ops)
+ blk_mq_end_io(rq, error);
+ else
+ __blk_end_request_all(rq, error);
break;
default:
BUG();
}
- return blk_kick_flush(q) | queued;
+ kicked = blk_kick_flush(q);
+ /* blk_mq_run_flush will run queue */
+ if (q->mq_ops)
+ return queued;
+ return kicked | queued;
}
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];
+ struct list_head *running;
bool queued = false;
struct request *rq, *n;
+ unsigned long flags = 0;
+ if (q->mq_ops) {
+ blk_mq_free_request(flush_rq);
+ spin_lock_irqsave(&q->mq_flush_lock, flags);
+ }
+ running = &q->flush_queue[q->flush_running_idx];
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);
+
+ if (!q->mq_ops)
+ 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) {
@@ -223,9 +262,48 @@ static void flush_end_io(struct request *flush_rq, int error)
* directly into request_fn may confuse the driver. Always use
* kblockd.
*/
- if (queued || q->flush_queue_delayed)
- blk_run_queue_async(q);
+ if (queued || q->flush_queue_delayed) {
+ if (!q->mq_ops)
+ blk_run_queue_async(q);
+ else
+ /*
+ * This can be optimized to only run queues with requests
+ * queued if necessary.
+ */
+ blk_mq_run_queues(q, true);
+ }
q->flush_queue_delayed = 0;
+ if (q->mq_ops)
+ spin_unlock_irqrestore(&q->mq_flush_lock, flags);
+}
+
+static void mq_flush_work(struct work_struct *work)
+{
+ struct request_queue *q;
+ struct request *rq;
+
+ q = container_of(work, struct request_queue, mq_flush_work);
+
+ /* We don't need set REQ_FLUSH_SEQ, it's for consistency */
+ rq = blk_mq_alloc_request(q, WRITE_FLUSH|REQ_FLUSH_SEQ,
+ __GFP_WAIT|GFP_ATOMIC);
+ rq->cmd_type = REQ_TYPE_FS;
+ rq->end_io = flush_end_io;
+
+ blk_mq_run_request(rq, true, false);
+}
+
+/*
+ * We can't directly use q->flush_rq, because it doesn't have tag and is not in
+ * hctx->rqs[]. so we must allocate a new request, since we can't sleep here,
+ * so offload the work to workqueue.
+ *
+ * Note: we assume a flush request finished in any hardware queue will flush
+ * the whole disk cache.
+ */
+static void mq_run_flush(struct request_queue *q)
+{
+ kblockd_schedule_work(q, &q->mq_flush_work);
}
/**
@@ -236,7 +314,7 @@ static void flush_end_io(struct request *flush_rq, int error)
* Please read the comment at the top of this file for more info.
*
* CONTEXT:
- * spin_lock_irq(q->queue_lock)
+ * spin_lock_irq(q->queue_lock or q->mq_flush_lock)
*
* RETURNS:
* %true if flush was issued, %false otherwise.
@@ -261,13 +339,18 @@ static bool blk_kick_flush(struct request_queue *q)
* Issue flush and toggle pending_idx. This makes pending_idx
* different from running_idx, which means flush is in flight.
*/
+ q->flush_pending_idx ^= 1;
+ if (q->mq_ops) {
+ mq_run_flush(q);
+ return true;
+ }
+
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;
list_add_tail(&q->flush_rq.queuelist, &q->queue_head);
return true;
}
@@ -284,16 +367,37 @@ static void flush_data_end_io(struct request *rq, int error)
blk_run_queue_async(q);
}
+static void mq_flush_data_end_io(struct request *rq, int error)
+{
+ struct request_queue *q = rq->q;
+ struct blk_mq_hw_ctx *hctx;
+ struct blk_mq_ctx *ctx;
+ unsigned long flags;
+
+ ctx = rq->mq_ctx;
+ hctx = q->mq_ops->map_queue(q, ctx->cpu);
+
+ /*
+ * After populating an empty queue, kick it to avoid stall. Read
+ * the comment in flush_end_io().
+ */
+ spin_lock_irqsave(&q->mq_flush_lock, flags);
+ if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error))
+ blk_mq_run_hw_queue(hctx, true);
+ spin_unlock_irqrestore(&q->mq_flush_lock, flags);
+}
+
/**
* blk_insert_flush - insert a new FLUSH/FUA request
* @rq: request to insert
*
* To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
+ * or __blk_mq_run_hw_queue() to dispatch request.
* @rq is being submitted. Analyze what needs to be done and put it on the
* right queue.
*
* CONTEXT:
- * spin_lock_irq(q->queue_lock)
+ * spin_lock_irq(q->queue_lock) in !mq case
*/
void blk_insert_flush(struct request *rq)
{
@@ -316,7 +420,10 @@ void blk_insert_flush(struct request *rq)
* complete the request.
*/
if (!policy) {
- __blk_end_bidi_request(rq, 0, 0, 0);
+ if (q->mq_ops)
+ blk_mq_end_io(rq, 0);
+ else
+ __blk_end_bidi_request(rq, 0, 0, 0);
return;
}
@@ -329,7 +436,10 @@ void blk_insert_flush(struct request *rq)
*/
if ((policy & REQ_FSEQ_DATA) &&
!(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
- list_add_tail(&rq->queuelist, &q->queue_head);
+ if (q->mq_ops) {
+ blk_mq_run_request(rq, false, true);
+ } else
+ list_add_tail(&rq->queuelist, &q->queue_head);
return;
}
@@ -341,6 +451,14 @@ void blk_insert_flush(struct request *rq)
INIT_LIST_HEAD(&rq->flush.list);
rq->cmd_flags |= REQ_FLUSH_SEQ;
rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
+ if (q->mq_ops) {
+ rq->end_io = mq_flush_data_end_io;
+
+ spin_lock_irq(&q->mq_flush_lock);
+ blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
+ spin_unlock_irq(&q->mq_flush_lock);
+ return;
+ }
rq->end_io = flush_data_end_io;
blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
@@ -453,3 +571,9 @@ int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
return ret;
}
EXPORT_SYMBOL(blkdev_issue_flush);
+
+void blk_mq_init_flush(struct request_queue *q)
+{
+ spin_lock_init(&q->mq_flush_lock);
+ INIT_WORK(&q->mq_flush_work, mq_flush_work);
+}
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