The attached patch will correct the ordering of trace output between
request queue insertions (I) and unplug calls (U). Right now the insert
precedes the unplug, which just isn't right:
65,128 0 1 67.699868965 7882 Q R 0 + 1 [aiod]
65,128 0 2 67.699876462 7882 G R 0 + 1 [aiod]
65,128 0 3 67.699878286 7882 P W [aiod]
65,128 0 4 67.699880491 7882 I R 0 + 1 [aiod]
65,128 0 5 67.699887589 7882 U R [aiod] 1
65,128 0 6 67.699898317 54 D R 0 + 1 [kblockd/0]
65,128 2 153 67.700126590 0 C R 0 + 1 [0]
With the patch provided the unplug comes first:
65,128 3 1 0.000000000 7045 Q R 0 + 1 [aiod]
65,128 3 2 0.000002295 7045 G R 0 + 1 [aiod]
65,128 3 3 0.000002617 7045 P W [aiod]
65,128 3 4 0.000003685 7045 U R [aiod] 1
65,128 3 5 0.000004107 7045 I R 0 + 1 [aiod]
65,128 3 6 0.000009491 57 D R 0 + 1 [kblockd/3]
65,128 2 1 0.000232447 0 C R 0 + 1 [0]
Jens: If you agree, the patch can be applied to your plug branch for
git://git.kernel.dk/data/git/linux-2.6-block.git
Thanks,
Alan
From: Alan D. Brunelle <[email protected]>
Fix unplug/insert trace inversion problem.
Signed-off-by: Alan D. Brunelle <[email protected]>
---
block/ll_rw_blk.c | 8 ++++----
include/linux/blkdev.h | 1 +
2 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 46d29f7..3bec97f 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -2981,6 +2981,7 @@ out_unlock:
if (bio_data_dir(bio) == WRITE && ioc->qrcu_idx == -1)
ioc->qrcu_idx = qrcu_read_lock(&q->qrcu);
list_add_tail(&req->queuelist, &ioc->plugged_list);
+ ioc->plugged_list_len++;
}
out:
@@ -3720,7 +3721,6 @@ void blk_unplug_current(void)
struct io_context *ioc = current->io_context;
struct request *req;
request_queue_t *q;
- int nr_unplug;
if (!ioc)
return;
@@ -3735,19 +3735,19 @@ void blk_unplug_current(void)
if (list_empty(&ioc->plugged_list))
goto out;
- nr_unplug = 0;
+ blk_add_trace_pdu_int(q, BLK_TA_UNPLUG_IO, NULL, ioc->plugged_list_len);
+
spin_lock_irq(q->queue_lock);
do {
req = list_entry_rq(ioc->plugged_list.next);
list_del_init(&req->queuelist);
add_request(q, req);
- nr_unplug++;
} while (!list_empty(&ioc->plugged_list));
+ ioc->plugged_list_len = 0;
spin_unlock_irq(q->queue_lock);
queue_delayed_work(kblockd_workqueue, &q->delay_work, 0);
- blk_add_trace_pdu_int(q, BLK_TA_UNPLUG_IO, NULL, nr_unplug);
out:
/*
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index f8cdd44..848564c 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -113,6 +113,7 @@ struct io_context {
*/
int plugged;
int qrcu_idx;
+ int plugged_list_len;
struct list_head plugged_list;
struct request_queue *plugged_queue;
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