md: use generic io stats accounting functions to simplify io stat accounting

Use generic io stats accounting help functions (generic_{start,end}_io_acct)
to simplify io stat accounting.

Signed-off-by: Gu Zheng <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/md/dm.c

···
 	struct mapped_device *md = io->md;
 	struct bio *bio = io->bio;
 	unsigned long duration = jiffies - io->start_time;
-	int pending, cpu;
+	int pending;
 	int rw = bio_data_dir(bio);
 
-	cpu = part_stat_lock();
-	part_round_stats(cpu, &dm_disk(md)->part0);
-	part_stat_add(cpu, &dm_disk(md)->part0, ticks[rw], duration);
-	part_stat_unlock();
+	generic_end_io_acct(rw, &dm_disk(md)->part0, io->start_time);
 
 	if (unlikely(dm_stats_used(&md->stats)))
 		dm_stats_account_io(&md->stats, bio->bi_rw, bio->bi_iter.bi_sector,
···
 {
 	int rw = bio_data_dir(bio);
 	struct mapped_device *md = q->queuedata;
-	int cpu;
 	int srcu_idx;
 	struct dm_table *map;
 
 	map = dm_get_live_table(md, &srcu_idx);
 
-	cpu = part_stat_lock();
-	part_stat_inc(cpu, &dm_disk(md)->part0, ios[rw]);
-	part_stat_add(cpu, &dm_disk(md)->part0, sectors[rw], bio_sectors(bio));
-	part_stat_unlock();
+	generic_start_io_acct(rw, bio_sectors(bio), &dm_disk(md)->part0);
 
 	/* if we're suspended, we have to queue this io for later */
 	if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))) {

drivers/md/md.c

···
 {
 	const int rw = bio_data_dir(bio);
 	struct mddev *mddev = q->queuedata;
-	int cpu;
 	unsigned int sectors;
 
 	if (mddev == NULL || mddev->pers == NULL
···
 	sectors = bio_sectors(bio);
 	mddev->pers->make_request(mddev, bio);
 
-	cpu = part_stat_lock();
-	part_stat_inc(cpu, &mddev->gendisk->part0, ios[rw]);
-	part_stat_add(cpu, &mddev->gendisk->part0, sectors[rw], sectors);
-	part_stat_unlock();
+	generic_start_io_acct(rw, sectors, &mddev->gendisk->part0);
 
 	if (atomic_dec_and_test(&mddev->active_io) && mddev->suspended)
 		wake_up(&mddev->sb_wait);