block: account iowait time when waiting for completion of IO request
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>
diff --git a/block/blk-exec.c b/block/blk-exec.c
index 74638ec..f634de7 100644
--- a/block/blk-exec.c
+++ b/block/blk-exec.c
@@ -120,9 +120,9 @@
/* 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;