Commit 5577022f authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Jens Axboe
Browse files

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: default avatarVladimir Davydov <vdavydov@parallels.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 686855f5

block/blk-exec.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

block/blk-flush.c

+1 −1
Original line number Diff line number Diff line
@@ -436,7 +436,7 @@ int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask, 


	bio_get(bio);

	submit_bio(WRITE_FLUSH, bio);

	wait_for_completion(&wait);

	wait_for_completion_io(&wait);



	/*

	 * The driver must store the error location in ->bi_sector, if

block/blk-lib.c

+3 −3
Original line number Diff line number Diff line
@@ -126,7 +126,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector, 


	/* 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 @@ int blkdev_issue_write_same(struct block_device *bdev, sector_t sector, 


	/* 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 @@ int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector, 


	/* 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.*/

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