Messages in this thread Patch in this message | | | Date | Mon, 18 Oct 2010 17:28:20 +0900 | From | Yasuaki Ishimatsu <> | Subject | [PATCH v4] blk: fix a wrong accounting of hd_struct->in_flight |
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Hi Jens,
> This looks good! To quiesce the queue, something like the below. > Completely untested.
Thank you for your advice. I applied your idea to the patch.
Regards, Yasuaki Ishimatsu ===
From: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
/proc/diskstats would display a strange output as follows.
$ cat /proc/diskstats |grep sda 8 0 sda 90524 7579 102154 20464 0 0 0 0 0 14096 20089 8 1 sda1 19085 1352 21841 4209 0 0 0 0 4294967064 15689 4293424691 ~~~~~~~~~~ 8 2 sda2 71252 3624 74891 15950 0 0 0 0 232 23995 1562390 8 3 sda3 54 487 2188 92 0 0 0 0 0 88 92 8 4 sda4 4 0 8 0 0 0 0 0 0 0 0 8 5 sda5 81 2027 2130 138 0 0 0 0 0 87 137
Its reason is the wrong way of accounting hd_struct->in_flight. When a bio is merged into a request belongs to different partition by ELEVATOR_FRONT_MERGE.
The detailed root cause is as follows.
Assuming that there are two partition, sda1 and sda2.
1. A request for sda2 is in request_queue. Hence sda1's hd_struct->in_flight is 0 and sda2's one is 1.
| hd_struct->in_flight --------------------------- sda1 | 0 sda2 | 1 ---------------------------
2. A bio belongs to sda1 is issued and is merged into the request mentioned on step1 by ELEVATOR_BACK_MERGE. The first sector of the request is changed from sda2 region to sda1 region. However the two partition's hd_struct->in_flight are not changed.
| hd_struct->in_flight --------------------------- sda1 | 0 sda2 | 1 ---------------------------
3. The request is finished and blk_account_io_done() is called. In this case, sda2's hd_struct->in_flight, not a sda1's one, is decremented.
| hd_struct->in_flight --------------------------- sda1 | -1 sda2 | 1 ---------------------------
The patch fixes the problem.
Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> --- block/blk-core.c | 24 ++++++++++++++++-------- block/blk-merge.c | 2 +- block/blk.h | 4 ---- block/genhd.c | 5 +++++ fs/partitions/check.c | 5 +++++ include/linux/blkdev.h | 1 + include/linux/elevator.h | 2 ++ 7 files changed, 30 insertions(+), 13 deletions(-)
Index: linux-2.6.36-rc7/block/blk-core.c =================================================================== --- linux-2.6.36-rc7.orig/block/blk-core.c 2010-10-15 09:21:37.000000000 +0900 +++ linux-2.6.36-rc7/block/blk-core.c 2010-10-18 14:45:19.000000000 +0900 @@ -64,13 +64,15 @@ static void drive_stat_acct(struct reque return;
cpu = part_stat_lock(); - part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
- if (!new_io) + if (!new_io) { + part = rq->part; part_stat_inc(cpu, part, merges[rw]); - else { + } else { + part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq)); part_round_stats(cpu, part); part_inc_in_flight(part, rw); + rq->part = part; }
part_stat_unlock(); @@ -128,6 +130,7 @@ void blk_rq_init(struct request_queue *q rq->ref_count = 1; rq->start_time = jiffies; set_start_time_ns(rq); + rq->part = NULL; } EXPORT_SYMBOL(blk_rq_init);
@@ -796,11 +799,16 @@ static struct request *get_request(struc rl->starved[is_sync] = 0;
priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags); - if (priv) + if (priv) { rl->elvpriv++;
- if (blk_queue_io_stat(q)) - rw_flags |= REQ_IO_STAT; + /* + * Don't do stats for non-priv requests + */ + 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); @@ -1759,7 +1767,7 @@ static void blk_account_io_completion(st int cpu;
cpu = part_stat_lock(); - part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req)); + part = req->part; part_stat_add(cpu, part, sectors[rw], bytes >> 9); part_stat_unlock(); } @@ -1779,7 +1787,7 @@ static void blk_account_io_done(struct r int cpu;
cpu = part_stat_lock(); - part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req)); + part = req->part;
part_stat_inc(cpu, part, ios[rw]); part_stat_add(cpu, part, ticks[rw], duration); Index: linux-2.6.36-rc7/block/blk-merge.c =================================================================== --- linux-2.6.36-rc7.orig/block/blk-merge.c 2010-10-07 05:39:52.000000000 +0900 +++ linux-2.6.36-rc7/block/blk-merge.c 2010-10-18 14:41:03.000000000 +0900 @@ -343,7 +343,7 @@ static void blk_account_io_merge(struct int cpu;
cpu = part_stat_lock(); - part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req)); + part = req->part;
part_round_stats(cpu, part); part_dec_in_flight(part, rq_data_dir(req)); Index: linux-2.6.36-rc7/include/linux/blkdev.h =================================================================== --- linux-2.6.36-rc7.orig/include/linux/blkdev.h 2010-10-15 09:21:37.000000000 +0900 +++ linux-2.6.36-rc7/include/linux/blkdev.h 2010-10-15 09:26:22.000000000 +0900 @@ -115,6 +115,7 @@ struct request { void *elevator_private3;
struct gendisk *rq_disk; + struct hd_struct *part; unsigned long start_time; #ifdef CONFIG_BLK_CGROUP unsigned long long start_time_ns; Index: linux-2.6.36-rc7/block/genhd.c =================================================================== --- linux-2.6.36-rc7.orig/block/genhd.c 2010-10-07 05:39:52.000000000 +0900 +++ linux-2.6.36-rc7/block/genhd.c 2010-10-18 14:38:04.000000000 +0900 @@ -944,12 +944,17 @@ static void disk_replace_part_tbl(struct struct disk_part_tbl *new_ptbl) { struct disk_part_tbl *old_ptbl = disk->part_tbl; + struct request_queue *q = disk->queue;
rcu_assign_pointer(disk->part_tbl, new_ptbl);
if (old_ptbl) { rcu_assign_pointer(old_ptbl->last_lookup, NULL); + spin_lock_irq(q->queue_lock); + elv_quiesce_start(q); call_rcu(&old_ptbl->rcu_head, disk_free_ptbl_rcu_cb); + elv_quiesce_end(q); + spin_unlock_irq(q->queue_lock); } }
Index: linux-2.6.36-rc7/fs/partitions/check.c =================================================================== --- linux-2.6.36-rc7.orig/fs/partitions/check.c 2010-10-07 05:39:52.000000000 +0900 +++ linux-2.6.36-rc7/fs/partitions/check.c 2010-10-18 16:19:58.000000000 +0900 @@ -375,6 +375,7 @@ void delete_partition(struct gendisk *di { struct disk_part_tbl *ptbl = disk->part_tbl; struct hd_struct *part; + struct request_queue *q = disk->queue;
if (partno >= ptbl->len) return; @@ -389,7 +390,11 @@ void delete_partition(struct gendisk *di kobject_put(part->holder_dir); device_del(part_to_dev(part));
+ spin_lock_irq(q->queue_lock); + elv_quiesce_start(disk->queue); call_rcu(&part->rcu_head, delete_partition_rcu_cb); + elv_quiesce_end(disk->queue); + spin_unlock_irq(q->queue_lock); }
static ssize_t whole_disk_show(struct device *dev, Index: linux-2.6.36-rc7/block/blk.h =================================================================== --- linux-2.6.36-rc7.orig/block/blk.h 2010-10-07 05:39:52.000000000 +0900 +++ linux-2.6.36-rc7/block/blk.h 2010-10-18 16:22:47.000000000 +0900 @@ -110,10 +110,6 @@ void blk_queue_congestion_threshold(stru
int blk_dev_init(void);
-void elv_quiesce_start(struct request_queue *q); -void elv_quiesce_end(struct request_queue *q); - - /* * Return the threshold (number of used requests) at which the queue is * considered to be congested. It include a little hysteresis to keep the Index: linux-2.6.36-rc7/include/linux/elevator.h =================================================================== --- linux-2.6.36-rc7.orig/include/linux/elevator.h 2010-10-07 05:39:52.000000000 +0900 +++ linux-2.6.36-rc7/include/linux/elevator.h 2010-10-18 17:09:58.000000000 +0900 @@ -121,6 +121,8 @@ extern void elv_completed_request(struct extern int elv_set_request(struct request_queue *, struct request *, gfp_t); extern void elv_put_request(struct request_queue *, struct request *); extern void elv_drain_elevator(struct request_queue *); +extern void elv_quiesce_start(struct request_queue *); +extern void elv_quiesce_end(struct request_queue *);
/* * io scheduler registration
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