block: simplify I/O stat accounting

This simplifies I/O stat accounting switching code and separates it
completely from I/O scheduler switch code.

Requests are accounted according to the state of their request queue
at the time of the request allocation. There is no need anymore to
flush the request queue when switching I/O accounting state.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

5 files changed, 12 insertions, 13 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 07ab75403e1a..2998fe3a2377 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -643,7 +643,7 @@ static inline void blk_free_request(struct request_queue *q, struct request *rq)
 }
 
 static struct request *
-blk_alloc_request(struct request_queue *q, int rw, int priv, gfp_t gfp_mask)
+blk_alloc_request(struct request_queue *q, int flags, int priv, gfp_t gfp_mask)
 {
         struct request *rq = mempool_alloc(q->rq.rq_pool, gfp_mask);
 
@@ -652,7 +652,7 @@ blk_alloc_request(struct request_queue *q, int rw, int priv, gfp_t gfp_mask)
 
         blk_rq_init(q, rq);
 
-        rq->cmd_flags = rw | REQ_ALLOCED;
+        rq->cmd_flags = flags | REQ_ALLOCED;
 
         if (priv) {
                 if (unlikely(elv_set_request(q, rq, gfp_mask))) {
@@ -792,6 +792,8 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
         if (priv)
                 rl->elvpriv++;
 
+        if (blk_queue_io_stat(q))
+                rw_flags |= REQ_IO_STAT;
         spin_unlock_irq(q->queue_lock);
 
         rq = blk_alloc_request(q, rw_flags, priv, gfp_mask);
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 63760ca3da0f..23d2a6fe34a3 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -402,7 +402,10 @@ static int attempt_merge(struct request_queue *q, struct request *req,
 
         elv_merge_requests(q, req, next);
 
-        blk_account_io_merge(req);
+        /*
+         * 'next' is going away, so update stats accordingly
+         */
+        blk_account_io_merge(next);
 
         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
         if (blk_rq_cpu_valid(next))
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index cac4e9febe6a..3ff9bba3379a 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -209,14 +209,10 @@ static ssize_t queue_iostats_store(struct request_queue *q, const char *page,
         ssize_t ret = queue_var_store(&stats, page, count);
 
         spin_lock_irq(q->queue_lock);
-        elv_quiesce_start(q);
-
         if (stats)
                 queue_flag_set(QUEUE_FLAG_IO_STAT, q);
         else
                 queue_flag_clear(QUEUE_FLAG_IO_STAT, q);
-
-        elv_quiesce_end(q);
         spin_unlock_irq(q->queue_lock);
 
         return ret;
diff --git a/block/blk.h b/block/blk.h
index 5dfc41267a08..79c85f7c9ff5 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -114,12 +114,7 @@ static inline int blk_cpu_to_group(int cpu)
 
 static inline int blk_do_io_stat(struct request *rq)
 {
-        struct gendisk *disk = rq->rq_disk;
-
-        if (!disk || !disk->queue)
-                return 0;
-
-        return blk_queue_io_stat(disk->queue) && (rq->cmd_flags & REQ_ELVPRIV);
+        return rq->rq_disk && blk_rq_io_stat(rq);
 }
 
 #endif
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ba54c834a590..2755d5c6da22 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -118,6 +118,7 @@ enum rq_flag_bits {
         __REQ_COPY_USER,        /* contains copies of user pages */
         __REQ_INTEGRITY,        /* integrity metadata has been remapped */
         __REQ_NOIDLE,           /* Don't anticipate more IO after this one */
+        __REQ_IO_STAT,          /* account I/O stat */
         __REQ_NR_BITS,          /* stops here */
 };
 
@@ -145,6 +146,7 @@ enum rq_flag_bits {
 #define REQ_COPY_USER   (1 << __REQ_COPY_USER)
 #define REQ_INTEGRITY   (1 << __REQ_INTEGRITY)
 #define REQ_NOIDLE      (1 << __REQ_NOIDLE)
+#define REQ_IO_STAT     (1 << __REQ_IO_STAT)
 
 #define BLK_MAX_CDB     16
 
@@ -598,6 +600,7 @@ enum {
                                  blk_failfast_transport(rq) ||  \
                                  blk_failfast_driver(rq))
 #define blk_rq_started(rq)      ((rq)->cmd_flags & REQ_STARTED)
+#define blk_rq_io_stat(rq)      ((rq)->cmd_flags & REQ_IO_STAT)
 
 #define blk_account_rq(rq)      (blk_rq_started(rq) && (blk_fs_request(rq) || blk_discard_rq(rq)))