block: account iowait time when waiting for completion of IO request
Vladimir Davydov [Thu, 14 Feb 2013 14:19:59 +0000 (18:19 +0400)]
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>

block/blk-exec.c
block/blk-flush.c
block/blk-lib.c

index 74638ec..f634de7 100644 (file)
@@ -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;
index 720ad60..db8f1b5 100644 (file)
@@ -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
index b3a1f2b..d6f50d5 100644 (file)
@@ -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.*/