Messages in this thread Patch in this message |  | | | Date | Thu, 14 Oct 2010 21:48:28 +0900 | | From | Yasuaki Ishimatsu <> | | Subject | [PATCH v2] blk: fix a wrong accounting of hd_struct->in_flight |
| |
Hi, Jens, Kosaki,
Thank you for your comments. I fixed the patch. How about it?
Thanks, 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 | 11 +++++++++-- include/linux/blkdev.h | 1 + 2 files changed, 10 insertions(+), 2 deletions(-) Index: linux-2.6.36-rc7/include/linux/blkdev.h =================================================================== --- linux-2.6.36-rc7.orig/include/linux/blkdev.h 2010-10-07 05:39:52.000000000 +0900 +++ linux-2.6.36-rc7/include/linux/blkdev.h 2010-10-14 17:37:33.000000000 +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/blk-core.c =================================================================== --- linux-2.6.36-rc7.orig/block/blk-core.c 2010-10-07 05:39:52.000000000 +0900 +++ linux-2.6.36-rc7/block/blk-core.c 2010-10-14 17:25:43.000000000 +0900 @@ -66,9 +66,15 @@ static void drive_stat_acct(struct reque cpu = part_stat_lock(); part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
- if (!new_io) + if (!new_io) { + if (unlikely(rq->part != part)) { + part_dec_in_flight(rq->part, rw); + part_inc_in_flight(part, rw); + rq->part = part; + } part_stat_inc(cpu, part, merges[rw]); - else { + } else { + rq->part = part; part_round_stats(cpu, part); part_inc_in_flight(part, rw); } @@ -128,6 +134,7 @@ 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);
|  |