Messages in this thread Patch in this message | | | Date | Fri, 15 Oct 2010 17:39:58 +0900 | From | Yasuaki Ishimatsu <> | Subject | [PATCH v3] blk: fix a wrong accounting of hd_struct->in_flight |
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Hi Jens,
Jens Axboe wrote: > On 2010-10-14 14:48, Yasuaki Ishimatsu wrote: >> 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); >> } > > I was thinking that we'd do away with the lookup always if ->part was > already set. It will probably require a quiscing of IO on partition > table reload, though.
O.K. I removed extra part lookups. Following patch also fixed a wrong accounting of hd_struct->in_flight. But I could not invent how to stop IOs when reloading partition table. Do you have some idea?
Thsanks, 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 | 13 ++++++++----- block/blk-merge.c | 2 +- include/linux/blkdev.h | 1 + 3 files changed, 10 insertions(+), 6 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 2010-10-15 09:44:23.000000000 +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);
@@ -1759,7 +1762,7 @@ 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 +1782,7 @@ 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 2010-10-15 09:38:45.000000000 +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 = rq->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;
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