[PATCH v5 10/10] blk-mq: support per-distpatch_queue flush machinery

Ming Lei
2014-09-25T15:24:50Z

This patch supports to run one single flush machinery for
each blk-mq dispatch queue, so that:

- current init_request and exit_request callbacks can
cover flush request too, then the buggy copying way of
initializing flush request's pdu can be fixed

- flushing performance gets improved in case of multi hw-queue

In fio sync write test over virtio-blk(4 hw queues, ioengine=sync,
iodepth=64, numjobs=4, bs=4K), it is observed that througput gets
increased a lot over my test environment:
- throughput: +70% in case of virtio-blk over null_blk
- throughput: +30% in case of virtio-blk over SSD image

The multi virtqueue feature isn't merged to QEMU yet, and patches for
the feature can be found in below tree:

git://kernel.ubuntu.com/ming/qemu.git v2.1.0-mq.4

And simply passing 'num_queues=4 vectors=5' should be enough to
enable multi queue(quad queue) feature for QEMU virtio-blk.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
block/blk-core.c | 2 +-
block/blk-flush.c | 21 +++++++++++++-------
block/blk-mq.c | 50 +++++++++++++++++++++++-------------------------
block/blk-sysfs.c | 4 ++--
block/blk.h | 16 +++++++++++++---
include/linux/blk-mq.h | 6 ++++++
6 files changed, 60 insertions(+), 39 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 6d7ece9..9acfd8e 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -704,7 +704,7 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
if (!q)
return NULL;

- q->fq = blk_alloc_flush_queue(q);
+ q->fq = blk_alloc_flush_queue(q, NUMA_NO_NODE, 0);
if (!q->fq)
return NULL;

diff --git a/block/blk-flush.c b/block/blk-flush.c
index 004d95e..20badd7 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -305,8 +305,15 @@ static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
fq->flush_pending_idx ^= 1;

blk_rq_init(q, flush_rq);
- if (q->mq_ops)
- blk_mq_clone_flush_request(flush_rq, first_rq);
+
+ /*
+ * Borrow tag from the first request since they can't
+ * be in flight at the same time.
+ */
+ if (q->mq_ops) {
+ flush_rq->mq_ctx = first_rq->mq_ctx;
+ flush_rq->tag = first_rq->tag;
+ }

flush_rq->cmd_type = REQ_TYPE_FS;
flush_rq->cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;
@@ -480,22 +487,22 @@ int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
}
EXPORT_SYMBOL(blkdev_issue_flush);

-struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q)
+struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
+ int node, int cmd_size)
{
struct blk_flush_queue *fq;
int rq_sz = sizeof(struct request);

- fq = kzalloc(sizeof(*fq), GFP_KERNEL);
+ fq = kzalloc_node(sizeof(*fq), GFP_KERNEL, node);
if (!fq)
goto fail;

if (q->mq_ops) {
spin_lock_init(&fq->mq_flush_lock);
- rq_sz = round_up(rq_sz + q->tag_set->cmd_size,
- cache_line_size());
+ rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
}

- fq->flush_rq = kzalloc(rq_sz, GFP_KERNEL);
+ fq->flush_rq = kzalloc_node(rq_sz, GFP_KERNEL, node);
if (!fq->flush_rq)
goto fail_rq;

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7c903ae..6c00855 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -281,26 +281,6 @@ void blk_mq_free_request(struct request *rq)
__blk_mq_free_request(hctx, ctx, rq);
}

-/*
- * Clone all relevant state from a request that has been put on hold in
- * the flush state machine into the preallocated flush request that hangs
- * off the request queue.
- *
- * For a driver the flush request should be invisible, that's why we are
- * impersonating the original request here.
- */
-void blk_mq_clone_flush_request(struct request *flush_rq,
- struct request *orig_rq)
-{
- struct blk_mq_hw_ctx *hctx =
- orig_rq->q->mq_ops->map_queue(orig_rq->q, orig_rq->mq_ctx->cpu);
-
- flush_rq->mq_ctx = orig_rq->mq_ctx;
- flush_rq->tag = orig_rq->tag;
- memcpy(blk_mq_rq_to_pdu(flush_rq), blk_mq_rq_to_pdu(orig_rq),
- hctx->cmd_size);
-}
-
inline void __blk_mq_end_request(struct request *rq, int error)
{
blk_account_io_done(rq);
@@ -1516,12 +1496,20 @@ static void blk_mq_exit_hctx(struct request_queue *q,
struct blk_mq_tag_set *set,
struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
{
+ unsigned flush_start_tag = set->queue_depth;
+
blk_mq_tag_idle(hctx);

+ if (set->ops->exit_request)
+ set->ops->exit_request(set->driver_data,
+ hctx->fq->flush_rq, hctx_idx,
+ flush_start_tag + hctx_idx);
+
if (set->ops->exit_hctx)
set->ops->exit_hctx(hctx, hctx_idx);

blk_mq_unregister_cpu_notifier(&hctx->cpu_notifier);
+ blk_free_flush_queue(hctx->fq);
kfree(hctx->ctxs);
blk_mq_free_bitmap(&hctx->ctx_map);
}
@@ -1556,6 +1544,7 @@ static int blk_mq_init_hctx(struct request_queue *q,
struct blk_mq_hw_ctx *hctx, unsigned hctx_idx)
{
int node;
+ unsigned flush_start_tag = set->queue_depth;

node = hctx->numa_node;
if (node == NUMA_NO_NODE)
@@ -1594,8 +1583,23 @@ static int blk_mq_init_hctx(struct request_queue *q,
set->ops->init_hctx(hctx, set->driver_data, hctx_idx))
goto free_bitmap;

+ hctx->fq = blk_alloc_flush_queue(q, hctx->numa_node, set->cmd_size);
+ if (!hctx->fq)
+ goto exit_hctx;
+
+ if (set->ops->init_request &&
+ set->ops->init_request(set->driver_data,
+ hctx->fq->flush_rq, hctx_idx,
+ flush_start_tag + hctx_idx, node))
+ goto free_fq;
+
return 0;

+ free_fq:
+ kfree(hctx->fq);
+ exit_hctx:
+ if (set->ops->exit_hctx)
+ set->ops->exit_hctx(hctx, hctx_idx);
free_bitmap:
blk_mq_free_bitmap(&hctx->ctx_map);
free_ctxs:
@@ -1863,16 +1867,10 @@ struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set)

blk_mq_add_queue_tag_set(set, q);

- q->fq = blk_alloc_flush_queue(q);
- if (!q->fq)
- goto err_hw_queues;
-
blk_mq_map_swqueue(q);

return q;

-err_hw_queues:
- blk_mq_exit_hw_queues(q, set, set->nr_hw_queues);
err_hw:
blk_cleanup_queue(q);
err_hctxs:
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 718cffc4c..e8f38a3 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -517,10 +517,10 @@ static void blk_release_queue(struct kobject *kobj)
if (q->queue_tags)
__blk_queue_free_tags(q);

- blk_free_flush_queue(q->fq);
-
if (q->mq_ops)
blk_mq_free_queue(q);
+ else
+ blk_free_flush_queue(q->fq);

blk_trace_shutdown(q);

diff --git a/block/blk.h b/block/blk.h
index 7ecdd85..43b0361 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -2,6 +2,8 @@
#define BLK_INTERNAL_H

#include <linux/idr.h>
+#include <linux/blk-mq.h>
+#include "blk-mq.h"

/* Amount of time in which a process may batch requests */
#define BLK_BATCH_TIME (HZ/50UL)
@@ -31,7 +33,14 @@ extern struct ida blk_queue_ida;
static inline struct blk_flush_queue *blk_get_flush_queue(
struct request_queue *q, struct blk_mq_ctx *ctx)
{
- return q->fq;
+ struct blk_mq_hw_ctx *hctx;
+
+ if (!q->mq_ops)
+ return q->fq;
+
+ hctx = q->mq_ops->map_queue(q, ctx->cpu);
+
+ return hctx->fq;
}

static inline void __blk_get_queue(struct request_queue *q)
@@ -39,8 +48,9 @@ static inline void __blk_get_queue(struct request_queue *q)
kobject_get(&q->kobj);
}

-struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q);
-void blk_free_flush_queue(struct blk_flush_queue *fq);
+struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
+ int node, int cmd_size);
+void blk_free_flush_queue(struct blk_flush_queue *q);

int blk_init_rl(struct request_list *rl, struct request_queue *q,
gfp_t gfp_mask);
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 3253495..02c5d95 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -4,6 +4,7 @@
#include <linux/blkdev.h>

struct blk_mq_tags;
+struct blk_flush_queue;

struct blk_mq_cpu_notifier {
struct list_head list;
@@ -34,6 +35,7 @@ struct blk_mq_hw_ctx {

struct request_queue *queue;
unsigned int queue_num;
+ struct blk_flush_queue *fq;

void *driver_data;

@@ -119,6 +121,10 @@ struct blk_mq_ops {
/*
* Called for every command allocated by the block layer to allow
* the driver to set up driver specific data.
+ *
+ * Tag greater than or equal to queue_depth is for setting up
+ * flush request.
+ *
* Ditto for exit/teardown.
*/
init_request_fn *init_request;
--
1.7.9.5