OpenZFS 6531 - Provide mechanism to artificially limit disk performance

Reviewed by: Paul Dagnelie <[email protected]>
Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: George Wilson <[email protected]>
Approved by: Dan McDonald <[email protected]>
Ported by: Tony Hutter <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>

OpenZFS-issue: https://www.illumos.org/issues/6531
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/97e8130

Porting notes:
- Added new IO delay tracepoints, and moved common ZIO tracepoint macros
  to a new trace_common.h file.
- Used zio_delay_taskq() in place of OpenZFS's timeout_generic() function.
- Updated zinject man page
- Updated zpool_scrub test files

1 files changed, 245 insertions, 14 deletions

diff --git a/module/zfs/zio_inject.c b/module/zfs/zio_inject.c
index 1458be477..61b7d25e6 100644
--- a/module/zfs/zio_inject.c
+++ b/module/zfs/zio_inject.c
@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
  */
 
 /*
@@ -49,15 +49,53 @@
 
 uint32_t zio_injection_enabled = 0;
 
+/*
+ * Data describing each zinject handler registered on the system, and
+ * contains the list node linking the handler in the global zinject
+ * handler list.
+ */
 typedef struct inject_handler {
 	int			zi_id;
 	spa_t			*zi_spa;
 	zinject_record_t	zi_record;
+	uint64_t		*zi_lanes;
+	int			zi_next_lane;
 	list_node_t		zi_link;
 } inject_handler_t;
 
+/*
+ * List of all zinject handlers registered on the system, protected by
+ * the inject_lock defined below.
+ */
 static list_t inject_handlers;
+
+/*
+ * This protects insertion into, and traversal of, the inject handler
+ * list defined above; as well as the inject_delay_count. Any time a
+ * handler is inserted or removed from the list, this lock should be
+ * taken as a RW_WRITER; and any time traversal is done over the list
+ * (without modification to it) this lock should be taken as a RW_READER.
+ */
 static krwlock_t inject_lock;
+
+/*
+ * This holds the number of zinject delay handlers that have been
+ * registered on the system. It is protected by the inject_lock defined
+ * above. Thus modifications to this count must be a RW_WRITER of the
+ * inject_lock, and reads of this count must be (at least) a RW_READER
+ * of the lock.
+ */
+static int inject_delay_count = 0;
+
+/*
+ * This lock is used only in zio_handle_io_delay(), refer to the comment
+ * in that function for more details.
+ */
+static kmutex_t inject_delay_mtx;
+
+/*
+ * Used to assign unique identifying numbers to each new zinject handler.
+ */
 static int inject_next_id = 1;
 
 /*
@@ -361,21 +399,70 @@ spa_handle_ignored_writes(spa_t *spa)
 	rw_exit(&inject_lock);
 }
 
-uint64_t
+hrtime_t
 zio_handle_io_delay(zio_t *zio)
 {
 	vdev_t *vd = zio->io_vd;
+	inject_handler_t *min_handler = NULL;
+	hrtime_t min_target = 0;
 	inject_handler_t *handler;
-	uint64_t seconds = 0;
-
-	if (zio_injection_enabled == 0)
-		return (0);
+	hrtime_t idle;
+	hrtime_t busy;
+	hrtime_t target;
 
 	rw_enter(&inject_lock, RW_READER);
 
-	for (handler = list_head(&inject_handlers); handler != NULL;
-	    handler = list_next(&inject_handlers, handler)) {
+	/*
+	 * inject_delay_count is a subset of zio_injection_enabled that
+	 * is only incremented for delay handlers. These checks are
+	 * mainly added to remind the reader why we're not explicitly
+	 * checking zio_injection_enabled like the other functions.
+	 */
+	IMPLY(inject_delay_count > 0, zio_injection_enabled > 0);
+	IMPLY(zio_injection_enabled == 0, inject_delay_count == 0);
+
+	/*
+	 * If there aren't any inject delay handlers registered, then we
+	 * can short circuit and simply return 0 here. A value of zero
+	 * informs zio_delay_interrupt() that this request should not be
+	 * delayed. This short circuit keeps us from acquiring the
+	 * inject_delay_mutex unnecessarily.
+	 */
+	if (inject_delay_count == 0) {
+		rw_exit(&inject_lock);
+		return (0);
+	}
+
+	/*
+	 * Each inject handler has a number of "lanes" associated with
+	 * it. Each lane is able to handle requests independently of one
+	 * another, and at a latency defined by the inject handler
+	 * record's zi_timer field. Thus if a handler in configured with
+	 * a single lane with a 10ms latency, it will delay requests
+	 * such that only a single request is completed every 10ms. So,
+	 * if more than one request is attempted per each 10ms interval,
+	 * the average latency of the requests will be greater than
+	 * 10ms; but if only a single request is submitted each 10ms
+	 * interval the average latency will be 10ms.
+	 *
+	 * We need to acquire this mutex to prevent multiple concurrent
+	 * threads being assigned to the same lane of a given inject
+	 * handler. The mutex allows us to perform the following two
+	 * operations atomically:
+	 *
+	 *	1. determine the minimum handler and minimum target
+	 *	   value of all the possible handlers
+	 *	2. update that minimum handler's lane array
+	 *
+	 * Without atomicity, two (or more) threads could pick the same
+	 * lane in step (1), and then conflict with each other in step
+	 * (2). This could allow a single lane handler to process
+	 * multiple requests simultaneously, which shouldn't be possible.
+	 */
+	mutex_enter(&inject_delay_mtx);
 
+	for (handler = list_head(&inject_handlers);
+	    handler != NULL; handler = list_next(&inject_handlers, handler)) {
 		if (handler->zi_record.zi_cmd != ZINJECT_DELAY_IO)
 			continue;
 
@@ -384,14 +471,101 @@ zio_handle_io_delay(zio_t *zio)
 			continue;
 		}
 
-		if (vd->vdev_guid == handler->zi_record.zi_guid) {
-			seconds = handler->zi_record.zi_timer;
-			break;
+		if (vd->vdev_guid != handler->zi_record.zi_guid)
+			continue;
+
+		/*
+		 * Defensive; should never happen as the array allocation
+		 * occurs prior to inserting this handler on the list.
+		 */
+		ASSERT3P(handler->zi_lanes, !=, NULL);
+
+		/*
+		 * This should never happen, the zinject command should
+		 * prevent a user from setting an IO delay with zero lanes.
+		 */
+		ASSERT3U(handler->zi_record.zi_nlanes, !=, 0);
+
+		ASSERT3U(handler->zi_record.zi_nlanes, >,
+		    handler->zi_next_lane);
+
+		/*
+		 * We want to issue this IO to the lane that will become
+		 * idle the soonest, so we compare the soonest this
+		 * specific handler can complete the IO with all other
+		 * handlers, to find the lowest value of all possible
+		 * lanes. We then use this lane to submit the request.
+		 *
+		 * Since each handler has a constant value for its
+		 * delay, we can just use the "next" lane for that
+		 * handler; as it will always be the lane with the
+		 * lowest value for that particular handler (i.e. the
+		 * lane that will become idle the soonest). This saves a
+		 * scan of each handler's lanes array.
+		 *
+		 * There's two cases to consider when determining when
+		 * this specific IO request should complete. If this
+		 * lane is idle, we want to "submit" the request now so
+		 * it will complete after zi_timer milliseconds. Thus,
+		 * we set the target to now + zi_timer.
+		 *
+		 * If the lane is busy, we want this request to complete
+		 * zi_timer milliseconds after the lane becomes idle.
+		 * Since the 'zi_lanes' array holds the time at which
+		 * each lane will become idle, we use that value to
+		 * determine when this request should complete.
+		 */
+		idle = handler->zi_record.zi_timer + gethrtime();
+		busy = handler->zi_record.zi_timer +
+		    handler->zi_lanes[handler->zi_next_lane];
+		target = MAX(idle, busy);
+
+		if (min_handler == NULL) {
+			min_handler = handler;
+			min_target = target;
+			continue;
 		}
 
+		ASSERT3P(min_handler, !=, NULL);
+		ASSERT3U(min_target, !=, 0);
+
+		/*
+		 * We don't yet increment the "next lane" variable since
+		 * we still might find a lower value lane in another
+		 * handler during any remaining iterations. Once we're
+		 * sure we've selected the absolute minimum, we'll claim
+		 * the lane and increment the handler's "next lane"
+		 * field below.
+		 */
+
+		if (target < min_target) {
+			min_handler = handler;
+			min_target = target;
+		}
 	}
+
+	/*
+	 * 'min_handler' will be NULL if no IO delays are registered for
+	 * this vdev, otherwise it will point to the handler containing
+	 * the lane that will become idle the soonest.
+	 */
+	if (min_handler != NULL) {
+		ASSERT3U(min_target, !=, 0);
+		min_handler->zi_lanes[min_handler->zi_next_lane] = min_target;
+
+		/*
+		 * If we've used all possible lanes for this handler,
+		 * loop back and start using the first lane again;
+		 * otherwise, just increment the lane index.
+		 */
+		min_handler->zi_next_lane = (min_handler->zi_next_lane + 1) %
+		    min_handler->zi_record.zi_nlanes;
+	}
+
+	mutex_exit(&inject_delay_mtx);
 	rw_exit(&inject_lock);
-	return (seconds);
+
+	return (min_target);
 }
 
 /*
@@ -415,6 +589,24 @@ zio_inject_fault(char *name, int flags, int *id, zinject_record_t *record)
 		if ((error = spa_reset(name)) != 0)
 			return (error);
 
+	if (record->zi_cmd == ZINJECT_DELAY_IO) {
+		/*
+		 * A value of zero for the number of lanes or for the
+		 * delay time doesn't make sense.
+		 */
+		if (record->zi_timer == 0 || record->zi_nlanes == 0)
+			return (SET_ERROR(EINVAL));
+
+		/*
+		 * The number of lanes is directly mapped to the size of
+		 * an array used by the handler. Thus, to ensure the
+		 * user doesn't trigger an allocation that's "too large"
+		 * we cap the number of lanes here.
+		 */
+		if (record->zi_nlanes >= UINT16_MAX)
+			return (SET_ERROR(EINVAL));
+	}
+
 	if (!(flags & ZINJECT_NULL)) {
 		/*
 		 * spa_inject_ref() will add an injection reference, which will
@@ -426,11 +618,34 @@ zio_inject_fault(char *name, int flags, int *id, zinject_record_t *record)
 
 		handler = kmem_alloc(sizeof (inject_handler_t), KM_SLEEP);
 
+		handler->zi_spa = spa;
+		handler->zi_record = *record;
+
+		if (handler->zi_record.zi_cmd == ZINJECT_DELAY_IO) {
+			handler->zi_lanes = kmem_zalloc(
+			    sizeof (*handler->zi_lanes) *
+			    handler->zi_record.zi_nlanes, KM_SLEEP);
+			handler->zi_next_lane = 0;
+		} else {
+			handler->zi_lanes = NULL;
+			handler->zi_next_lane = 0;
+		}
+
 		rw_enter(&inject_lock, RW_WRITER);
 
+		/*
+		 * We can't move this increment into the conditional
+		 * above because we need to hold the RW_WRITER lock of
+		 * inject_lock, and we don't want to hold that while
+		 * allocating the handler's zi_lanes array.
+		 */
+		if (handler->zi_record.zi_cmd == ZINJECT_DELAY_IO) {
+			ASSERT3S(inject_delay_count, >=, 0);
+			inject_delay_count++;
+			ASSERT3S(inject_delay_count, >, 0);
+		}
+
 		*id = handler->zi_id = inject_next_id++;
-		handler->zi_spa = spa;
-		handler->zi_record = *record;
 		list_insert_tail(&inject_handlers, handler);
 		atomic_inc_32(&zio_injection_enabled);
 
@@ -508,9 +723,23 @@ zio_clear_fault(int id)
 		return (SET_ERROR(ENOENT));
 	}
 
+	if (handler->zi_record.zi_cmd == ZINJECT_DELAY_IO) {
+		ASSERT3S(inject_delay_count, >, 0);
+		inject_delay_count--;
+		ASSERT3S(inject_delay_count, >=, 0);
+	}
+
 	list_remove(&inject_handlers, handler);
 	rw_exit(&inject_lock);
 
+	if (handler->zi_record.zi_cmd == ZINJECT_DELAY_IO) {
+		ASSERT3P(handler->zi_lanes, !=, NULL);
+		kmem_free(handler->zi_lanes, sizeof (*handler->zi_lanes) *
+		    handler->zi_record.zi_nlanes);
+	} else {
+		ASSERT3P(handler->zi_lanes, ==, NULL);
+	}
+
 	spa_inject_delref(handler->zi_spa);
 	kmem_free(handler, sizeof (inject_handler_t));
 	atomic_dec_32(&zio_injection_enabled);
@@ -522,6 +751,7 @@ void
 zio_inject_init(void)
 {
 	rw_init(&inject_lock, NULL, RW_DEFAULT, NULL);
+	mutex_init(&inject_delay_mtx, NULL, MUTEX_DEFAULT, NULL);
 	list_create(&inject_handlers, sizeof (inject_handler_t),
 	    offsetof(inject_handler_t, zi_link));
 }
@@ -530,6 +760,7 @@ void
 zio_inject_fini(void)
 {
 	list_destroy(&inject_handlers);
+	mutex_destroy(&inject_delay_mtx);
 	rw_destroy(&inject_lock);
 }