blk-mq: support per-distpatch_queue flush machinery

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>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/blk-core.c b/block/blk-core.c
index b1dd4e0..e1c2775 100644 (file)
--- 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 (file)
--- 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 53b6def..4e7a314 100644 (file)
--- 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:
@@ -1862,16 +1866,10 @@ 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 718cffc..e8f38a3 100644 (file)
--- 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 (file)
--- 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 (file)
--- 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;