Revert part of "Log I/Os longer than zio_delay_max (30s default)"

This reverts commit 9dcb97198338ba2d8764dd5604b278118612f74
which was originally introduced to debug occasional slow I/Os.
These I/Os would complete eventually but were observed to take
several 100 seconds.

The root cause of this issue was the CFQ scheduler which can,
under certain conditions, excessively delay an I/O from being
issued to the device.  This issue was mitigated somewhat by
commit 84daaddedbfc9cf4bd1490d8a6f4b2967051e308 which ensures
the I/O elevator gets changed even for DM style devices.

This change isn't in any way harmful but it does conflict with
a required change to properly account from I/O wait time.
Because Linux does not export the io_schedule_timeout() function
we must instead rely  on io_schedule() via cv_wait_io().

The additional debugging information which was added to the
delay event has been intentionally left in place.

Signed-off-by: Brian Behlendorf <[email protected]>

1 files changed, 10 insertions, 22 deletions

diff --git a/module/zfs/zio.c b/module/zfs/zio.c
index bcfc081d1..ece3329d0 100644
--- a/module/zfs/zio.c
+++ b/module/zfs/zio.c
@@ -1305,34 +1305,18 @@ __zio_execute(zio_t *zio)
 int
 zio_wait(zio_t *zio)
 {
-	uint64_t timeout;
 	int error;
 
 	ASSERT(zio->io_stage == ZIO_STAGE_OPEN);
 	ASSERT(zio->io_executor == NULL);
 
 	zio->io_waiter = curthread;
-	timeout = ddi_get_lbolt() + (zio_delay_max / MILLISEC * hz);
 
 	__zio_execute(zio);
 
 	mutex_enter(&zio->io_lock);
-	while (zio->io_executor != NULL) {
-		/*
-		 * Wake up periodically to prevent the kernel from complaining
-		 * about a blocked task.  However, check zio_delay_max to see
-		 * if the I/O has exceeded the timeout and post an ereport.
-		 */
-		cv_timedwait_interruptible(&zio->io_cv, &zio->io_lock,
-		    ddi_get_lbolt() + hz);
-
-		if (timeout && (ddi_get_lbolt() > timeout)) {
-			zio->io_delay = zio_delay_max;
-			zfs_ereport_post(FM_EREPORT_ZFS_DELAY,
-			    zio->io_spa, zio->io_vd, zio, 0, 0);
-			timeout = 0;
-		}
-	}
+	while (zio->io_executor != NULL)
+		cv_wait(&zio->io_cv, &zio->io_lock);
 	mutex_exit(&zio->io_lock);
 
 	error = zio->io_error;
@@ -2905,11 +2889,15 @@ zio_done(zio_t *zio)
 	vdev_stat_update(zio, zio->io_size);
 
 	/*
-	 * When an I/O completes but was slow post an ereport.
+	 * If this I/O is attached to a particular vdev is slow, exeeding
+	 * 30 seconds to complete, post an error described the I/O delay.
+	 * We ignore these errors if the device is currently unavailable.
 	 */
-	if (zio->io_delay >= zio_delay_max)
-		zfs_ereport_post(FM_EREPORT_ZFS_DELAY, zio->io_spa,
-		    zio->io_vd, zio, 0, 0);
+	if (zio->io_delay >= zio_delay_max) {
+		if (zio->io_vd != NULL && !vdev_is_dead(zio->io_vd))
+			zfs_ereport_post(FM_EREPORT_ZFS_DELAY, zio->io_spa,
+                                         zio->io_vd, zio, 0, 0);
+	}
 
 	if (zio->io_error) {
 		/*