Re: Time sliced CFQ io scheduler

[Jens Axboe <axboe@suse.de>]

On Fri, Dec 03 2004, Jens Axboe wrote:
> > >So Prakash, please try the same test with those settings:
> > >
> > ># cd /sys/block/<dev>/queue/iosched
> > ># echo 6 > idle
> > ># echo 150 > slice
> > >
> > >These are the first I tried, there may be better settings. If you have
> > >your filesystem on dm/raid, you probably want to do the above for each
> > >device the dm/raid is composed of.
> > 
> > Yeas, I have linux raid (testing md1). Have appield both settings on 
> > both drives and got a interesting new pattern: Now it alternates. My 
> > email client is still not usale while writing though...
> 
> Funky. It looks like another case of the io scheduler being at the wrong
> place - if raid sends dependent reads to different drives, it screws up
> the io scheduling. The right way to fix that would be to io scheduler
> before raid (reverse of what we do now), but that is a lot of work. A
> hack would be to try and tie processes to one md component for periods
> of time, sort of like cfq slicing.

It makes sense to split the slice period for sync and async requests,
since async requests usually get a lot of requests queued in a short
period of time. Might even make sense to introduce a slice_rq value as
well, limiting the number of requests queued in a given slice.

But at least this patch lets you set slice_sync and slice_async
seperately, if you want to experiement.

===== drivers/block/cfq-iosched.c 1.15 vs edited =====
--- 1.15/drivers/block/cfq-iosched.c	2004-11-30 07:56:58 +01:00
+++ edited/drivers/block/cfq-iosched.c	2004-12-03 11:36:09 +01:00
@@ -22,21 +22,23 @@
 #include <linux/rbtree.h>
 #include <linux/mempool.h>
 
-static unsigned long max_elapsed_crq;
-static unsigned long max_elapsed_dispatch;
-
 /*
  * tunables
  */
 static int cfq_quantum = 4;		/* max queue in one round of service */
 static int cfq_queued = 8;		/* minimum rq allocate limit per-queue*/
-static int cfq_service = HZ;		/* period over which service is avg */
 static int cfq_fifo_expire_r = HZ / 2;	/* fifo timeout for sync requests */
 static int cfq_fifo_expire_w = 5 * HZ;	/* fifo timeout for async requests */
 static int cfq_fifo_rate = HZ / 8;	/* fifo expiry rate */
 static int cfq_back_max = 16 * 1024;	/* maximum backwards seek, in KiB */
 static int cfq_back_penalty = 2;	/* penalty of a backwards seek */
 
+static int cfq_slice_sync = HZ / 10;
+static int cfq_slice_async = HZ / 25;
+static int cfq_idle = HZ / 249;
+
+static int cfq_max_depth = 4;
+
 /*
  * for the hash of cfqq inside the cfqd
  */
@@ -55,6 +57,7 @@
 #define list_entry_hash(ptr)	hlist_entry((ptr), struct cfq_rq, hash)
 
 #define list_entry_cfqq(ptr)	list_entry((ptr), struct cfq_queue, cfq_list)
+#define list_entry_fifo(ptr)	list_entry((ptr), struct request, queuelist)
 
 #define RQ_DATA(rq)		(rq)->elevator_private
 
@@ -76,22 +79,18 @@
 #define rq_rb_key(rq)		(rq)->sector
 
 /*
- * threshold for switching off non-tag accounting
- */
-#define CFQ_MAX_TAG		(4)
-
-/*
  * sort key types and names
  */
 enum {
 	CFQ_KEY_PGID,
 	CFQ_KEY_TGID,
+	CFQ_KEY_PID,
 	CFQ_KEY_UID,
 	CFQ_KEY_GID,
 	CFQ_KEY_LAST,
 };
 
-static char *cfq_key_types[] = { "pgid", "tgid", "uid", "gid", NULL };
+static char *cfq_key_types[] = { "pgid", "tgid", "pid", "uid", "gid", NULL };
 
 /*
  * spare queue
@@ -103,6 +102,8 @@
 static kmem_cache_t *cfq_ioc_pool;
 
 struct cfq_data {
+	atomic_t ref;
+
 	struct list_head rr_list;
 	struct list_head empty_list;
 
@@ -114,8 +115,6 @@
 
 	unsigned int max_queued;
 
-	atomic_t ref;
-
 	int key_type;
 
 	mempool_t *crq_pool;
@@ -127,6 +126,14 @@
 	int rq_in_driver;
 
 	/*
+	 * schedule slice state info
+	 */
+	struct timer_list timer;
+	struct work_struct unplug_work;
+	struct cfq_queue *active_queue;
+	unsigned int dispatch_slice;
+
+	/*
 	 * tunables, see top of file
 	 */
 	unsigned int cfq_quantum;
@@ -137,8 +144,9 @@
 	unsigned int cfq_back_penalty;
 	unsigned int cfq_back_max;
 	unsigned int find_best_crq;
-
-	unsigned int cfq_tagged;
+	unsigned int cfq_slice[2];
+	unsigned int cfq_idle;
+	unsigned int cfq_max_depth;
 };
 
 struct cfq_queue {
@@ -150,8 +158,6 @@
 	struct hlist_node cfq_hash;
 	/* hash key */
 	unsigned long key;
-	/* whether queue is on rr (or empty) list */
-	int on_rr;
 	/* on either rr or empty list of cfqd */
 	struct list_head cfq_list;
 	/* sorted list of pending requests */
@@ -169,10 +175,14 @@
 
 	int key_type;
 
-	unsigned long service_start;
-	unsigned long service_used;
+	unsigned long slice_start;
+	unsigned long slice_end;
+	unsigned long service_last;
 
-	unsigned int max_rate;
+	/* whether queue is on rr (or empty) list */
+	unsigned int on_rr : 1;
+	unsigned int wait_request : 1;
+	unsigned int must_dispatch : 1;
 
 	/* number of requests that have been handed to the driver */
 	int in_flight;
@@ -219,6 +229,8 @@
 		default:
 		case CFQ_KEY_TGID:
 			return tsk->tgid;
+		case CFQ_KEY_PID:
+			return tsk->pid;
 		case CFQ_KEY_UID:
 			return tsk->uid;
 		case CFQ_KEY_GID:
@@ -406,67 +418,22 @@
 		cfqq->next_crq = cfq_find_next_crq(cfqq->cfqd, cfqq, crq);
 }
 
-static int cfq_check_sort_rr_list(struct cfq_queue *cfqq)
-{
-	struct list_head *head = &cfqq->cfqd->rr_list;
-	struct list_head *next, *prev;
-
-	/*
-	 * list might still be ordered
-	 */
-	next = cfqq->cfq_list.next;
-	if (next != head) {
-		struct cfq_queue *cnext = list_entry_cfqq(next);
-
-		if (cfqq->service_used > cnext->service_used)
-			return 1;
-	}
-
-	prev = cfqq->cfq_list.prev;
-	if (prev != head) {
-		struct cfq_queue *cprev = list_entry_cfqq(prev);
-
-		if (cfqq->service_used < cprev->service_used)
-			return 1;
-	}
-
-	return 0;
-}
-
-static void cfq_sort_rr_list(struct cfq_queue *cfqq, int new_queue)
+static void cfq_resort_rr_list(struct cfq_queue *cfqq)
 {
 	struct list_head *entry = &cfqq->cfqd->rr_list;
 
-	if (!cfqq->on_rr)
-		return;
-	if (!new_queue && !cfq_check_sort_rr_list(cfqq))
-		return;
-
 	list_del(&cfqq->cfq_list);
 
 	/*
-	 * sort by our mean service_used, sub-sort by in-flight requests
+	 * sort by when queue was last serviced
 	 */
 	while ((entry = entry->prev) != &cfqq->cfqd->rr_list) {
 		struct cfq_queue *__cfqq = list_entry_cfqq(entry);
 
-		if (cfqq->service_used > __cfqq->service_used)
+		if (!__cfqq->service_last)
+			break;
+		if (time_before(__cfqq->service_last, cfqq->service_last))
 			break;
-		else if (cfqq->service_used == __cfqq->service_used) {
-			struct list_head *prv;
-
-			while ((prv = entry->prev) != &cfqq->cfqd->rr_list) {
-				__cfqq = list_entry_cfqq(prv);
-
-				WARN_ON(__cfqq->service_used > cfqq->service_used);
-				if (cfqq->service_used != __cfqq->service_used)
-					break;
-				if (cfqq->in_flight > __cfqq->in_flight)
-					break;
-
-				entry = prv;
-			}
-		}
 	}
 
 	list_add(&cfqq->cfq_list, entry);
@@ -479,16 +446,12 @@
 static inline void
 cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 {
-	/*
-	 * it's currently on the empty list
-	 */
-	cfqq->on_rr = 1;
-	cfqd->busy_queues++;
+	BUG_ON(cfqq->on_rr);
 
-	if (time_after(jiffies, cfqq->service_start + cfq_service))
-		cfqq->service_used >>= 3;
+	cfqd->busy_queues++;
+	cfqq->on_rr = 1;
 
-	cfq_sort_rr_list(cfqq, 1);
+	cfq_resort_rr_list(cfqq);
 }
 
 static inline void
@@ -512,10 +475,10 @@
 		struct cfq_data *cfqd = cfqq->cfqd;
 
 		BUG_ON(!cfqq->queued[crq->is_sync]);
+		cfqq->queued[crq->is_sync]--;
 
 		cfq_update_next_crq(crq);
 
-		cfqq->queued[crq->is_sync]--;
 		rb_erase(&crq->rb_node, &cfqq->sort_list);
 		RB_CLEAR_COLOR(&crq->rb_node);
 
@@ -622,11 +585,6 @@
 	if (crq) {
 		struct cfq_queue *cfqq = crq->cfq_queue;
 
-		if (cfqq->cfqd->cfq_tagged) {
-			cfqq->service_used--;
-			cfq_sort_rr_list(cfqq, 0);
-		}
-
 		crq->accounted = 0;
 		cfqq->cfqd->rq_in_driver--;
 	}
@@ -640,9 +598,7 @@
 	if (crq) {
 		cfq_remove_merge_hints(q, crq);
 		list_del_init(&rq->queuelist);
-
-		if (crq->cfq_queue)
-			cfq_del_crq_rb(crq);
+		cfq_del_crq_rb(crq);
 	}
 }
 
@@ -724,6 +680,98 @@
 }
 
 /*
+ * current cfqq expired its slice (or was too idle), select new one
+ */
+static inline void cfq_slice_expired(struct cfq_data *cfqd)
+{
+	struct cfq_queue *cfqq = cfqd->active_queue;
+	unsigned long now = jiffies;
+
+	if (cfqq) {
+		if (cfqq->wait_request)
+			del_timer(&cfqd->timer);
+
+		cfqq->service_last = now;
+		cfqq->must_dispatch = 0;
+
+		if (cfqq->on_rr)
+			cfq_resort_rr_list(cfqq);
+
+		cfqq = NULL;
+	}
+
+	if (!list_empty(&cfqd->rr_list)) {
+		cfqq = list_entry_cfqq(cfqd->rr_list.next);
+
+		cfqq->slice_start = now;
+		cfqq->slice_end = 0;
+		cfqq->wait_request = 0;
+	}
+
+	cfqd->active_queue = cfqq;
+	cfqd->dispatch_slice = 0;
+}
+
+static int cfq_arm_slice_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
+{
+	WARN_ON(!RB_EMPTY(&cfqq->sort_list));
+
+	cfqq->wait_request = 1;
+
+	if (!cfqd->cfq_idle)
+		return 0;
+
+	if (!timer_pending(&cfqd->timer)) {
+		unsigned long now = jiffies, slice_left;
+
+		slice_left = cfqq->slice_end - now;
+		cfqd->timer.expires = now + min(cfqd->cfq_idle,(unsigned int)slice_left);
+		add_timer(&cfqd->timer);
+	}
+
+	return 1;
+}
+
+/*
+ * get next queue for service
+ */
+static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
+{
+	struct cfq_queue *cfqq = cfqd->active_queue;
+	unsigned long now = jiffies;
+
+	cfqq = cfqd->active_queue;
+	if (!cfqq)
+		goto new_queue;
+
+	if (cfqq->must_dispatch)
+		goto must_queue;
+
+	/*
+	 * slice has expired
+	 */
+	if (time_after(jiffies, cfqq->slice_end))
+		goto new_queue;
+
+	/*
+	 * if queue has requests, dispatch one. if not, check if
+	 * enough slice is left to wait for one
+	 */
+must_queue:
+	if (!RB_EMPTY(&cfqq->sort_list))
+		goto keep_queue;
+	else if (cfqq->slice_end - now >= cfqd->cfq_idle) {
+		if (cfq_arm_slice_timer(cfqd, cfqq))
+			return NULL;
+	}
+
+new_queue:
+	cfq_slice_expired(cfqd);
+keep_queue:
+	return cfqd->active_queue;
+}
+
+/*
  * we dispatch cfqd->cfq_quantum requests in total from the rr_list queues,
  * this function sector sorts the selected request to minimize seeks. we start
  * at cfqd->last_sector, not 0.
@@ -741,9 +789,7 @@
 	list_del(&crq->request->queuelist);
 
 	last = cfqd->last_sector;
-	while ((entry = entry->prev) != head) {
-		__rq = list_entry_rq(entry);
-
+	list_for_each_entry_reverse(__rq, head, queuelist) {
 		if (blk_barrier_rq(crq->request))
 			break;
 		if (!blk_fs_request(crq->request))
@@ -777,95 +823,95 @@
 	if (time_before(now, cfqq->last_fifo_expire + cfqd->cfq_fifo_batch_expire))
 		return NULL;
 
-	crq = RQ_DATA(list_entry(cfqq->fifo[0].next, struct request, queuelist));
-	if (reads && time_after(now, crq->queue_start + cfqd->cfq_fifo_expire_r)) {
-		cfqq->last_fifo_expire = now;
-		return crq;
+	if (reads) {
+		crq = RQ_DATA(list_entry_fifo(cfqq->fifo[READ].next));
+		if (time_after(now, crq->queue_start + cfqd->cfq_fifo_expire_r)) {
+			cfqq->last_fifo_expire = now;
+			return crq;
+		}
 	}
 
-	crq = RQ_DATA(list_entry(cfqq->fifo[1].next, struct request, queuelist));
-	if (writes && time_after(now, crq->queue_start + cfqd->cfq_fifo_expire_w)) {
-		cfqq->last_fifo_expire = now;
-		return crq;
+	if (writes) {
+		crq = RQ_DATA(list_entry_fifo(cfqq->fifo[WRITE].next));
+		if (time_after(now, crq->queue_start + cfqd->cfq_fifo_expire_w)) {
+			cfqq->last_fifo_expire = now;
+			return crq;
+		}
 	}
 
 	return NULL;
 }
 
-/*
- * dispatch a single request from given queue
- */
-static inline void
-cfq_dispatch_request(request_queue_t *q, struct cfq_data *cfqd,
-		     struct cfq_queue *cfqq)
+static int
+__cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
+			int max_dispatch)
 {
-	struct cfq_rq *crq;
+	int dispatched = 0, sync = 0;
 
-	/*
-	 * follow expired path, else get first next available
-	 */
-	if ((crq = cfq_check_fifo(cfqq)) == NULL) {
-		if (cfqd->find_best_crq)
-			crq = cfqq->next_crq;
-		else
-			crq = rb_entry_crq(rb_first(&cfqq->sort_list));
-	}
+	BUG_ON(RB_EMPTY(&cfqq->sort_list));
+
+	do {
+		struct cfq_rq *crq;
+
+		/*
+		 * follow expired path, else get first next available
+		 */
+		if ((crq = cfq_check_fifo(cfqq)) == NULL) {
+			if (cfqd->find_best_crq)
+				crq = cfqq->next_crq;
+			else
+				crq = rb_entry_crq(rb_first(&cfqq->sort_list));
+		}
+
+		cfqd->last_sector = crq->request->sector + crq->request->nr_sectors;
+
+		/*
+		 * finally, insert request into driver list
+		 */
+		cfq_dispatch_sort(cfqd->queue, crq);
+
+		cfqd->dispatch_slice++;
+		dispatched++;
+		sync += crq->is_sync;
+
+		if (RB_EMPTY(&cfqq->sort_list))
+			break;
 
-	cfqd->last_sector = crq->request->sector + crq->request->nr_sectors;
+	} while (dispatched < max_dispatch);
 
 	/*
-	 * finally, insert request into driver list
+	 * if slice end isn't set yet, set it. if at least one request was
+	 * sync, use the sync time slice value
 	 */
-	cfq_dispatch_sort(q, crq);
+	if (!cfqq->slice_end)
+		cfqq->slice_end = cfqd->cfq_slice[!!sync] + jiffies;
+
+
+	return dispatched;
 }
 
 static int cfq_dispatch_requests(request_queue_t *q, int max_dispatch)
 {
 	struct cfq_data *cfqd = q->elevator->elevator_data;
 	struct cfq_queue *cfqq;
-	struct list_head *entry, *tmp;
-	int queued, busy_queues, first_round;
 
 	if (list_empty(&cfqd->rr_list))
 		return 0;
 
-	queued = 0;
-	first_round = 1;
-restart:
-	busy_queues = 0;
-	list_for_each_safe(entry, tmp, &cfqd->rr_list) {
-		cfqq = list_entry_cfqq(entry);
-
-		BUG_ON(RB_EMPTY(&cfqq->sort_list));
-
-		/*
-		 * first round of queueing, only select from queues that
-		 * don't already have io in-flight
-		 */
-		if (first_round && cfqq->in_flight)
-			continue;
-
-		cfq_dispatch_request(q, cfqd, cfqq);
-
-		if (!RB_EMPTY(&cfqq->sort_list))
-			busy_queues++;
-
-		queued++;
-	}
-
-	if ((queued < max_dispatch) && (busy_queues || first_round)) {
-		first_round = 0;
-		goto restart;
-	}
+	cfqq = cfq_select_queue(cfqd);
+	if (!cfqq)
+		return 0;
 
-	return queued;
+	cfqq->wait_request = 0;
+	cfqq->must_dispatch = 0;
+	del_timer(&cfqd->timer);
+	return __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);
 }
 
 static inline void cfq_account_dispatch(struct cfq_rq *crq)
 {
 	struct cfq_queue *cfqq = crq->cfq_queue;
 	struct cfq_data *cfqd = cfqq->cfqd;
-	unsigned long now, elapsed;
 
 	/*
 	 * accounted bit is necessary since some drivers will call
@@ -874,37 +920,9 @@
 	if (crq->accounted)
 		return;
 
-	now = jiffies;
-	if (cfqq->service_start == ~0UL)
-		cfqq->service_start = now;
-
-	/*
-	 * on drives with tagged command queueing, command turn-around time
-	 * doesn't necessarily reflect the time spent processing this very
-	 * command inside the drive. so do the accounting differently there,
-	 * by just sorting on the number of requests
-	 */
-	if (cfqd->cfq_tagged) {
-		if (time_after(now, cfqq->service_start + cfq_service)) {
-			cfqq->service_start = now;
-			cfqq->service_used /= 10;
-		}
-
-		cfqq->service_used++;
-		cfq_sort_rr_list(cfqq, 0);
-	}
-
-	elapsed = now - crq->queue_start;
-	if (elapsed > max_elapsed_dispatch)
-		max_elapsed_dispatch = elapsed;
-
 	crq->accounted = 1;
-	crq->service_start = now;
-
-	if (++cfqd->rq_in_driver >= CFQ_MAX_TAG && !cfqd->cfq_tagged) {
-		cfqq->cfqd->cfq_tagged = 1;
-		printk("cfq: depth %d reached, tagging now on\n", CFQ_MAX_TAG);
-	}
+	crq->service_start = jiffies;
+	cfqd->rq_in_driver++;
 }
 
 static inline void
@@ -915,21 +933,18 @@
 	WARN_ON(!cfqd->rq_in_driver);
 	cfqd->rq_in_driver--;
 
-	if (!cfqd->cfq_tagged) {
-		unsigned long now = jiffies;
-		unsigned long duration = now - crq->service_start;
-
-		if (time_after(now, cfqq->service_start + cfq_service)) {
-			cfqq->service_start = now;
-			cfqq->service_used >>= 3;
-		}
-
-		cfqq->service_used += duration;
-		cfq_sort_rr_list(cfqq, 0);
+	/*
+	 * queue was preempted while this request was servicing
+	 */
+	if (cfqd->active_queue != cfqq)
+		return;
 
-		if (duration > max_elapsed_crq)
-			max_elapsed_crq = duration;
-	}
+	/*
+	 * no requests. if last request was a sync request, wait for
+	 * a new one.
+	 */
+	if (RB_EMPTY(&cfqq->sort_list) && crq->is_sync)
+		cfq_arm_slice_timer(cfqd, cfqq);
 }
 
 static struct request *cfq_next_request(request_queue_t *q)
@@ -937,6 +952,9 @@
 	struct cfq_data *cfqd = q->elevator->elevator_data;
 	struct request *rq;
 
+	if (cfqd->rq_in_driver >= cfqd->cfq_max_depth)
+		return NULL;
+
 	if (!list_empty(&q->queue_head)) {
 		struct cfq_rq *crq;
 dispatch:
@@ -964,6 +982,8 @@
  */
 static void cfq_put_queue(struct cfq_queue *cfqq)
 {
+	struct cfq_data *cfqd = cfqq->cfqd;
+
 	BUG_ON(!atomic_read(&cfqq->ref));
 
 	if (!atomic_dec_and_test(&cfqq->ref))
@@ -972,6 +992,9 @@
 	BUG_ON(rb_first(&cfqq->sort_list));
 	BUG_ON(cfqq->on_rr);
 
+	if (unlikely(cfqd->active_queue == cfqq))
+		cfqd->active_queue = NULL;
+
 	cfq_put_cfqd(cfqq->cfqd);
 
 	/*
@@ -1117,6 +1140,7 @@
 		cic->ioc = ioc;
 		cic->cfqq = __cfqq;
 		atomic_inc(&__cfqq->ref);
+		atomic_inc(&cfqd->ref);
 	} else {
 		struct cfq_io_context *__cic;
 		unsigned long flags;
@@ -1159,10 +1183,10 @@
 		__cic->ioc = ioc;
 		__cic->cfqq = __cfqq;
 		atomic_inc(&__cfqq->ref);
+		atomic_inc(&cfqd->ref);
 		spin_lock_irqsave(&ioc->lock, flags);
 		list_add(&__cic->list, &cic->list);
 		spin_unlock_irqrestore(&ioc->lock, flags);
-
 		cic = __cic;
 		*cfqq = __cfqq;
 	}
@@ -1199,8 +1223,11 @@
 			new_cfqq = kmem_cache_alloc(cfq_pool, gfp_mask);
 			spin_lock_irq(cfqd->queue->queue_lock);
 			goto retry;
-		} else
-			goto out;
+		} else {
+			cfqq = kmem_cache_alloc(cfq_pool, gfp_mask);
+			if (!cfqq)
+				goto out;
+		}
 
 		memset(cfqq, 0, sizeof(*cfqq));
 
@@ -1216,7 +1243,7 @@
 		cfqq->cfqd = cfqd;
 		atomic_inc(&cfqd->ref);
 		cfqq->key_type = cfqd->key_type;
-		cfqq->service_start = ~0UL;
+		cfqq->service_last = 0;
 	}
 
 	if (new_cfqq)
@@ -1243,14 +1270,25 @@
 
 static void cfq_enqueue(struct cfq_data *cfqd, struct cfq_rq *crq)
 {
-	crq->is_sync = 0;
-	if (rq_data_dir(crq->request) == READ || current->flags & PF_SYNCWRITE)
-		crq->is_sync = 1;
+	struct cfq_queue *cfqq = crq->cfq_queue;
+	struct request *rq = crq->request;
+
+	crq->is_sync = rq_data_dir(rq) == READ || current->flags & PF_SYNCWRITE;
 
 	cfq_add_crq_rb(crq);
 	crq->queue_start = jiffies;
 
-	list_add_tail(&crq->request->queuelist, &crq->cfq_queue->fifo[crq->is_sync]);
+	list_add_tail(&rq->queuelist, &cfqq->fifo[crq->is_sync]);
+
+	/*
+	 * if we are waiting for a request for this queue, let it rip
+	 * immediately and flag that we must not expire this queue just now
+	 */
+	if (cfqq->wait_request && cfqq == cfqd->active_queue) {
+		cfqq->must_dispatch = 1;
+		del_timer(&cfqd->timer);
+		cfqd->queue->request_fn(cfqd->queue);
+	}
 }
 
 static void
@@ -1339,31 +1377,34 @@
 	struct cfq_data *cfqd = q->elevator->elevator_data;
 	struct cfq_queue *cfqq;
 	int ret = ELV_MQUEUE_MAY;
+	int limit;
 
 	if (current->flags & PF_MEMALLOC)
 		return ELV_MQUEUE_MAY;
 
 	cfqq = cfq_find_cfq_hash(cfqd, cfq_hash_key(cfqd, current));
-	if (cfqq) {
-		int limit = cfqd->max_queued;
-
-		if (cfqq->allocated[rw] < cfqd->cfq_queued)
-			return ELV_MQUEUE_MUST;
-
-		if (cfqd->busy_queues)
-			limit = q->nr_requests / cfqd->busy_queues;
-
-		if (limit < cfqd->cfq_queued)
-			limit = cfqd->cfq_queued;
-		else if (limit > cfqd->max_queued)
-			limit = cfqd->max_queued;
+	if (unlikely(!cfqq))
+		return ELV_MQUEUE_MAY;
 
-		if (cfqq->allocated[rw] >= limit) {
-			if (limit > cfqq->alloc_limit[rw])
-				cfqq->alloc_limit[rw] = limit;
+	if (cfqq->allocated[rw] < cfqd->cfq_queued)
+		return ELV_MQUEUE_MUST;
+	if (cfqq->wait_request)
+		return ELV_MQUEUE_MUST;
+
+	limit = cfqd->max_queued;
+	if (cfqd->busy_queues)
+		limit = q->nr_requests / cfqd->busy_queues;
+
+	if (limit < cfqd->cfq_queued)
+		limit = cfqd->cfq_queued;
+	else if (limit > cfqd->max_queued)
+		limit = cfqd->max_queued;
+
+	if (cfqq->allocated[rw] >= limit) {
+		if (limit > cfqq->alloc_limit[rw])
+			cfqq->alloc_limit[rw] = limit;
 
-			ret = ELV_MQUEUE_NO;
-		}
+		ret = ELV_MQUEUE_NO;
 	}
 
 	return ret;
@@ -1395,12 +1436,12 @@
 		BUG_ON(q->last_merge == rq);
 		BUG_ON(!hlist_unhashed(&crq->hash));
 
-		if (crq->io_context)
-			put_io_context(crq->io_context->ioc);
-
 		BUG_ON(!cfqq->allocated[crq->is_write]);
 		cfqq->allocated[crq->is_write]--;
 
+		if (crq->io_context)
+			put_io_context(crq->io_context->ioc);
+
 		mempool_free(crq, cfqd->crq_pool);
 		rq->elevator_private = NULL;
 
@@ -1473,6 +1514,7 @@
 		crq->is_write = rw;
 		rq->elevator_private = crq;
 		cfqq->alloc_limit[rw] = 0;
+		smp_mb();
 		return 0;
 	}
 
@@ -1486,6 +1528,44 @@
 	return 1;
 }
 
+static void cfq_kick_queue(void *data)
+{
+	request_queue_t *q = data;
+
+	blk_run_queue(q);
+}
+
+static void cfq_schedule_timer(unsigned long data)
+{
+	struct cfq_data *cfqd = (struct cfq_data *) data;
+	struct cfq_queue *cfqq;
+	unsigned long flags;
+
+	spin_lock_irqsave(cfqd->queue->queue_lock, flags);
+
+	if ((cfqq = cfqd->active_queue) != NULL) {
+		/*
+		 * expired
+		 */
+		if (time_after(jiffies, cfqq->slice_end))
+			goto out;
+
+		/*
+		 * not expired and it has a request pending, let it dispatch
+		 */
+		if (!RB_EMPTY(&cfqq->sort_list)) {
+			cfqq->must_dispatch = 1;
+			goto out_cont;
+		}
+	} 
+
+out:
+	cfq_slice_expired(cfqd);
+out_cont:
+	spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
+	kblockd_schedule_work(&cfqd->unplug_work);
+}
+
 static void cfq_put_cfqd(struct cfq_data *cfqd)
 {
 	request_queue_t *q = cfqd->queue;
@@ -1494,6 +1574,8 @@
 	if (!atomic_dec_and_test(&cfqd->ref))
 		return;
 
+	blk_sync_queue(q);
+
 	/*
 	 * kill spare queue, getting it means we have two refences to it.
 	 * drop both
@@ -1567,8 +1649,15 @@
 	q->nr_requests = 1024;
 	cfqd->max_queued = q->nr_requests / 16;
 	q->nr_batching = cfq_queued;
-	cfqd->key_type = CFQ_KEY_TGID;
+	cfqd->key_type = CFQ_KEY_PID;
 	cfqd->find_best_crq = 1;
+
+	init_timer(&cfqd->timer);
+	cfqd->timer.function = cfq_schedule_timer;
+	cfqd->timer.data = (unsigned long) cfqd;
+
+	INIT_WORK(&cfqd->unplug_work, cfq_kick_queue, q);
+
 	atomic_set(&cfqd->ref, 1);
 
 	cfqd->cfq_queued = cfq_queued;
@@ -1578,6 +1667,10 @@
 	cfqd->cfq_fifo_batch_expire = cfq_fifo_rate;
 	cfqd->cfq_back_max = cfq_back_max;
 	cfqd->cfq_back_penalty = cfq_back_penalty;
+	cfqd->cfq_slice[0] = cfq_slice_async;
+	cfqd->cfq_slice[1] = cfq_slice_sync;
+	cfqd->cfq_idle = cfq_idle;
+	cfqd->cfq_max_depth = cfq_max_depth;
 
 	return 0;
 out_spare:
@@ -1624,7 +1717,6 @@
 	return -ENOMEM;
 }
 
-
 /*
  * sysfs parts below -->
  */
@@ -1650,13 +1742,6 @@
 }
 
 static ssize_t
-cfq_clear_elapsed(struct cfq_data *cfqd, const char *page, size_t count)
-{
-	max_elapsed_dispatch = max_elapsed_crq = 0;
-	return count;
-}
-
-static ssize_t
 cfq_set_key_type(struct cfq_data *cfqd, const char *page, size_t count)
 {
 	spin_lock_irq(cfqd->queue->queue_lock);
@@ -1664,6 +1749,8 @@
 		cfqd->key_type = CFQ_KEY_PGID;
 	else if (!strncmp(page, "tgid", 4))
 		cfqd->key_type = CFQ_KEY_TGID;
+	else if (!strncmp(page, "pid", 3))
+		cfqd->key_type = CFQ_KEY_PID;
 	else if (!strncmp(page, "uid", 3))
 		cfqd->key_type = CFQ_KEY_UID;
 	else if (!strncmp(page, "gid", 3))
@@ -1704,6 +1791,10 @@
 SHOW_FUNCTION(cfq_find_best_show, cfqd->find_best_crq, 0);
 SHOW_FUNCTION(cfq_back_max_show, cfqd->cfq_back_max, 0);
 SHOW_FUNCTION(cfq_back_penalty_show, cfqd->cfq_back_penalty, 0);
+SHOW_FUNCTION(cfq_idle_show, cfqd->cfq_idle, 1);
+SHOW_FUNCTION(cfq_slice_async_show, cfqd->cfq_slice[0], 1);
+SHOW_FUNCTION(cfq_slice_sync_show, cfqd->cfq_slice[1], 1);
+SHOW_FUNCTION(cfq_max_depth_show, cfqd->cfq_max_depth, 0);
 #undef SHOW_FUNCTION
 
 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)			\
@@ -1729,6 +1820,10 @@
 STORE_FUNCTION(cfq_find_best_store, &cfqd->find_best_crq, 0, 1, 0);
 STORE_FUNCTION(cfq_back_max_store, &cfqd->cfq_back_max, 0, UINT_MAX, 0);
 STORE_FUNCTION(cfq_back_penalty_store, &cfqd->cfq_back_penalty, 1, UINT_MAX, 0);
+STORE_FUNCTION(cfq_idle_store, &cfqd->cfq_idle, 0, UINT_MAX, 1);
+STORE_FUNCTION(cfq_slice_async_store, &cfqd->cfq_slice[0], 1, UINT_MAX, 1);
+STORE_FUNCTION(cfq_slice_sync_store, &cfqd->cfq_slice[1], 1, UINT_MAX, 1);
+STORE_FUNCTION(cfq_max_depth_store, &cfqd->cfq_max_depth, 2, UINT_MAX, 0);
 #undef STORE_FUNCTION
 
 static struct cfq_fs_entry cfq_quantum_entry = {
@@ -1771,15 +1866,31 @@
 	.show = cfq_back_penalty_show,
 	.store = cfq_back_penalty_store,
 };
-static struct cfq_fs_entry cfq_clear_elapsed_entry = {
-	.attr = {.name = "clear_elapsed", .mode = S_IWUSR },
-	.store = cfq_clear_elapsed,
+static struct cfq_fs_entry cfq_slice_sync_entry = {
+	.attr = {.name = "slice_sync", .mode = S_IRUGO | S_IWUSR },
+	.show = cfq_slice_sync_show,
+	.store = cfq_slice_sync_store,
+};
+static struct cfq_fs_entry cfq_slice_async_entry = {
+	.attr = {.name = "slice_async", .mode = S_IRUGO | S_IWUSR },
+	.show = cfq_slice_async_show,
+	.store = cfq_slice_async_store,
+};
+static struct cfq_fs_entry cfq_idle_entry = {
+	.attr = {.name = "idle", .mode = S_IRUGO | S_IWUSR },
+	.show = cfq_idle_show,
+	.store = cfq_idle_store,
 };
 static struct cfq_fs_entry cfq_key_type_entry = {
 	.attr = {.name = "key_type", .mode = S_IRUGO | S_IWUSR },
 	.show = cfq_read_key_type,
 	.store = cfq_set_key_type,
 };
+static struct cfq_fs_entry cfq_max_depth_entry = {
+	.attr = {.name = "max_depth", .mode = S_IRUGO | S_IWUSR },
+	.show = cfq_max_depth_show,
+	.store = cfq_max_depth_store,
+};
 
 static struct attribute *default_attrs[] = {
 	&cfq_quantum_entry.attr,
@@ -1791,7 +1902,10 @@
 	&cfq_find_best_entry.attr,
 	&cfq_back_max_entry.attr,
 	&cfq_back_penalty_entry.attr,
-	&cfq_clear_elapsed_entry.attr,
+	&cfq_slice_sync_entry.attr,
+	&cfq_slice_async_entry.attr,
+	&cfq_idle_entry.attr,
+	&cfq_max_depth_entry.attr,
 	NULL,
 };
 
@@ -1856,7 +1970,7 @@
 	.elevator_owner =	THIS_MODULE,
 };
 
-int cfq_init(void)
+static int __init cfq_init(void)
 {
 	int ret;
 
@@ -1864,17 +1978,35 @@
 		return -ENOMEM;
 
 	ret = elv_register(&iosched_cfq);
-	if (!ret) {
-		__module_get(THIS_MODULE);
-		return 0;
-	}
+	if (ret)
+		cfq_slab_kill();
 
-	cfq_slab_kill();
 	return ret;
 }
 
 static void __exit cfq_exit(void)
 {
+	struct task_struct *g, *p;
+	unsigned long flags;
+
+	read_lock_irqsave(&tasklist_lock, flags);
+
+	/*
+	 * iterate each process in the system, removing our io_context
+	 */
+	do_each_thread(g, p) {
+		struct io_context *ioc = p->io_context;
+
+		if (ioc && ioc->cic) {
+			ioc->cic->exit(ioc->cic);
+			cfq_free_io_context(ioc->cic);
+			ioc->cic = NULL;
+		}
+
+	} while_each_thread(g, p);
+
+	read_unlock_irqrestore(&tasklist_lock, flags);
+
 	cfq_slab_kill();
 	elv_unregister(&iosched_cfq);
 }
 

-- 
Jens Axboe