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block: account iowait time when waiting for completion of IO request

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Using wait_for_completion() for waiting for a IO request to be executed
results in wrong iowait time accounting. For example, a system having
the only task doing write() and fdatasync() on a block device can be
reported being idle instead of iowaiting as it should because
blkdev_issue_flush() calls wait_for_completion() which in turn calls
schedule() that does not increment the iowait proc counter and thus does
not turn on iowait time accounting.

The patch makes block layer use wait_for_completion_io() instead of
wait_for_completion() where appropriate to account iowait time
correctly.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Vladimir Davydov
2013-02-14 18:19:59 +04:00
committed by Jens Axboe
parent 686855f5d8
commit 5577022f4e
3 changed files with 6 additions and 6 deletions
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4
block/blk-exec.c
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@@ -120,9 +120,9 @@ int blk_execute_rq(struct request_queue *q, struct gendisk *bd_disk,
/* Prevent hang_check timer from firing at us during very long I/O */
hang_check = sysctl_hung_task_timeout_secs;
if (hang_check)
while (!wait_for_completion_timeout(&wait, hang_check * (HZ/2)));
while (!wait_for_completion_io_timeout(&wait, hang_check * (HZ/2)));
else
wait_for_completion(&wait);
wait_for_completion_io(&wait);
if (rq->errors)
err = -EIO;