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-lib.c b/block/blk-lib.c
index b3a1f2b7..d6f50d5 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -126,7 +126,7 @@
/* Wait for bios in-flight */
if (!atomic_dec_and_test(&bb.done))
- wait_for_completion(&wait);
+ wait_for_completion_io(&wait);
if (!test_bit(BIO_UPTODATE, &bb.flags))
ret = -EIO;
@@ -200,7 +200,7 @@
/* Wait for bios in-flight */
if (!atomic_dec_and_test(&bb.done))
- wait_for_completion(&wait);
+ wait_for_completion_io(&wait);
if (!test_bit(BIO_UPTODATE, &bb.flags))
ret = -ENOTSUPP;
@@ -262,7 +262,7 @@
/* Wait for bios in-flight */
if (!atomic_dec_and_test(&bb.done))
- wait_for_completion(&wait);
+ wait_for_completion_io(&wait);
if (!test_bit(BIO_UPTODATE, &bb.flags))
/* One of bios in the batch was completed with error.*/
