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Time sliced CFQ #2

From:  Jens Axboe <axboe@suse.de>
To:  Linux Kernel <linux-kernel@vger.kernel.org>
Subject:  [PATCH] Time sliced CFQ #2
Date:  Sat, 4 Dec 2004 11:49:21 +0100
Cc:  Andrew Morton <akpm@osdl.org>

Hi,

Second version of the time sliced CFQ. Changes:

- Sync io has a fixed time slice like before, async io has both a time
  based and a request based slice limit. The queue slice is expired when
  one of these limits are reached.

- Fix a bug in invoking the request handler on a plugged queue.

- Drop the ->alloc_limit wakeup stuff, I'm not so sure it's a good idea
  and there are probably wakeup races buried there.

With the async rq slice limit, it behaves perfectly here for me with
readers competing with async writers. The main slice settings for a
queue are:

- slice_sync: How many msec a sync disk slice lasts
- slice_idle: How long a sync slice is allowed to idle
- slice_async: How many msec an async disk slice lasts
- slice_async_rq: How many requests an async disk slice lasts

Interestingly, cfq is now about 10% faster on an fsck than deadline and
as:

AS:

bart:~ # time fsck.ext2 -fy /dev/hdc1
e2fsck 1.34 (25-Jul-2003)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/hdc1: 36/3753600 files (8.3% non-contiguous), 644713/7504552 blocks

real    0m30.594s
user    0m1.862s
sys     0m5.214s


DEADLINE:

bart:~ # time fsck.ext2 -fy /dev/hdc1
e2fsck 1.34 (25-Jul-2003)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/hdc1: 36/3753600 files (8.3% non-contiguous), 644713/7504552 blocks

real    0m30.475s
user    0m1.855s
sys     0m5.280s


CFQ:

bart:~ # time fsck.ext2 -fy /dev/hdc1
e2fsck 1.34 (25-Jul-2003)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/hdc1: 36/3753600 files (8.3% non-contiguous), 644713/7504552 blocks

real    0m27.921s
user    0m1.846s
sys     0m5.648s


Patch is against 2.6.10-rc3.

Signed-off-by: Jens Axboe <axboe@suse.de>

===== 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	2004-12-04 11:41:42 +01:00
@@ -22,21 +22,24 @@
 #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_slice_async_rq = 8;
+static int cfq_slice_idle = HZ / 249;
+
+static int cfq_max_depth = 4;
+
 /*
  * for the hash of cfqq inside the cfqd
  */
@@ -55,6 +58,7 @@
 #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 +80,18 @@
 #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 +103,8 @@
 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 +116,6 @@
 
 	unsigned int max_queued;
 
-	atomic_t ref;
-
 	int key_type;
 
 	mempool_t *crq_pool;
@@ -127,6 +127,14 @@
 	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 +145,10 @@
 	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_slice_async_rq;
+	unsigned int cfq_slice_idle;
+	unsigned int cfq_max_depth;
 };
 
 struct cfq_queue {
@@ -150,8 +160,6 @@
 	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 */
@@ -169,15 +177,17 @@
 
 	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;
-	/* number of currently allocated requests */
-	int alloc_limit[2];
 };
 
 struct cfq_rq {
@@ -195,7 +205,6 @@
 	unsigned int in_flight : 1;
 	unsigned int accounted : 1;
 	unsigned int is_sync   : 1;
-	unsigned int is_write  : 1;
 };
 
 static struct cfq_queue *cfq_find_cfq_hash(struct cfq_data *, unsigned long);
@@ -219,6 +228,8 @@
 		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 +417,22 @@
 		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 +445,12 @@
 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 +474,10 @@
 		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 +584,6 @@
 	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 +597,7 @@
 	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 +679,99 @@
 }
 
 /*
+ * 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;
+		cfqq->wait_request = 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_slice_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_slice_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_slice_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 +823,100 @@
 	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;
+
+	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;
+
+	} while (dispatched < max_dispatch);
 
 	/*
-	 * follow expired path, else get first next available
+	 * if slice end isn't set yet, set it. if at least one request was
+	 * sync, use the sync time slice value
 	 */
-	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;
+	if (!cfqq->slice_end)
+		cfqq->slice_end = cfqd->cfq_slice[!!sync] + jiffies;
 
 	/*
-	 * finally, insert request into driver list
+	 * expire an async queue immediately if it has used up its tq slice
 	 */
-	cfq_dispatch_sort(q, crq);
+	if (!sync && cfqd->dispatch_slice >= cfqd->cfq_slice_async_rq)
+		cfq_slice_expired(cfqd);
+
+	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 +925,9 @@
 	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 +938,18 @@
 	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 +957,9 @@
 	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 +987,8 @@
  */
 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 +997,9 @@
 	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 +1145,7 @@
 		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 +1188,10 @@
 		__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 +1228,11 @@
 			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 +1248,7 @@
 		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 +1275,31 @@
 
 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) {
+		request_queue_t *q = cfqd->queue;
+
+		cfqq->must_dispatch = 1;
+		del_timer(&cfqd->timer);
+
+		if (!blk_queue_plugged(q))
+			q->request_fn(q);
+		else
+			__generic_unplug_device(q);
+	}
 }
 
 static void
@@ -1339,32 +1388,31 @@
 	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;
 
-			ret = ELV_MQUEUE_NO;
-		}
-	}
+	if (cfqq->allocated[rw] >= limit)
+		ret = ELV_MQUEUE_NO;
 
 	return ret;
 }
@@ -1372,12 +1420,13 @@
 static void cfq_check_waiters(request_queue_t *q, struct cfq_queue *cfqq)
 {
 	struct request_list *rl = &q->rq;
-	const int write = waitqueue_active(&rl->wait[WRITE]);
-	const int read = waitqueue_active(&rl->wait[READ]);
+	const int writes = waitqueue_active(&rl->wait[WRITE]);
+	const int reads = waitqueue_active(&rl->wait[READ]);
+	struct cfq_data *cfqd = q->elevator->elevator_data;
 
-	if (read && cfqq->allocated[READ] < cfqq->alloc_limit[READ])
+	if (reads && cfqq->allocated[READ] < cfqd->max_queued)
 		wake_up(&rl->wait[READ]);
-	if (write && cfqq->allocated[WRITE] < cfqq->alloc_limit[WRITE])
+	if (writes && cfqq->allocated[WRITE] < cfqd->max_queued)
 		wake_up(&rl->wait[WRITE]);
 }
 
@@ -1391,16 +1440,17 @@
 
 	if (crq) {
 		struct cfq_queue *cfqq = crq->cfq_queue;
+		const int rw = rq_data_dir(rq);
 
 		BUG_ON(q->last_merge == rq);
 		BUG_ON(!hlist_unhashed(&crq->hash));
 
+		BUG_ON(!cfqq->allocated[rw]);
+		cfqq->allocated[rw]--;
+
 		if (crq->io_context)
 			put_io_context(crq->io_context->ioc);
 
-		BUG_ON(!cfqq->allocated[crq->is_write]);
-		cfqq->allocated[crq->is_write]--;
-
 		mempool_free(crq, cfqd->crq_pool);
 		rq->elevator_private = NULL;
 
@@ -1470,9 +1520,7 @@
 		crq->io_context = cic;
 		crq->service_start = crq->queue_start = 0;
 		crq->in_flight = crq->accounted = crq->is_sync = 0;
-		crq->is_write = rw;
 		rq->elevator_private = crq;
-		cfqq->alloc_limit[rw] = 0;
 		return 0;
 	}
 
@@ -1486,6 +1534,44 @@
 	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 +1580,8 @@
 	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
@@ -1565,10 +1653,17 @@
 	 * some requests. fairness is handled differently
 	 */
 	q->nr_requests = 1024;
-	cfqd->max_queued = q->nr_requests / 16;
+	cfqd->max_queued = q->nr_requests / 8;
 	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 +1673,11 @@
 	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_slice_async_rq = cfq_slice_async_rq;
+	cfqd->cfq_slice_idle = cfq_slice_idle;
+	cfqd->cfq_max_depth = cfq_max_depth;
 
 	return 0;
 out_spare:
@@ -1624,7 +1724,6 @@
 	return -ENOMEM;
 }
 
-
 /*
  * sysfs parts below -->
  */
@@ -1650,13 +1749,6 @@
 }
 
 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 +1756,8 @@
 		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 +1798,11 @@
 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_slice_idle_show, cfqd->cfq_slice_idle, 1);
+SHOW_FUNCTION(cfq_slice_sync_show, cfqd->cfq_slice[1], 1);
+SHOW_FUNCTION(cfq_slice_async_show, cfqd->cfq_slice[0], 1);
+SHOW_FUNCTION(cfq_slice_async_rq_show, cfqd->cfq_slice_async_rq, 0);
+SHOW_FUNCTION(cfq_max_depth_show, cfqd->cfq_max_depth, 0);
 #undef SHOW_FUNCTION
 
 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)			\
@@ -1729,6 +1828,11 @@
 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_slice_idle_store, &cfqd->cfq_slice_idle, 0, UINT_MAX, 1);
+STORE_FUNCTION(cfq_slice_sync_store, &cfqd->cfq_slice[1], 1, UINT_MAX, 1);
+STORE_FUNCTION(cfq_slice_async_store, &cfqd->cfq_slice[0], 1, UINT_MAX, 1);
+STORE_FUNCTION(cfq_slice_async_rq_store, &cfqd->cfq_slice_async_rq, 1, UINT_MAX,
0);
+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 +1875,36 @@
 	.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_slice_async_rq_entry = {
+	.attr = {.name = "slice_async_rq", .mode = S_IRUGO | S_IWUSR },
+	.show = cfq_slice_async_rq_show,
+	.store = cfq_slice_async_rq_store,
+};
+static struct cfq_fs_entry cfq_slice_idle_entry = {
+	.attr = {.name = "slice_idle", .mode = S_IRUGO | S_IWUSR },
+	.show = cfq_slice_idle_show,
+	.store = cfq_slice_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 +1916,11 @@
 	&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_slice_async_rq_entry.attr,
+	&cfq_slice_idle_entry.attr,
+	&cfq_max_depth_entry.attr,
 	NULL,
 };
 
@@ -1856,7 +1985,7 @@
 	.elevator_owner =	THIS_MODULE,
 };
 
-int cfq_init(void)
+static int __init cfq_init(void)
 {
 	int ret;
 
@@ -1864,17 +1993,34 @@
 		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);
 }
===== drivers/block/ll_rw_blk.c 1.281 vs edited =====
--- 1.281/drivers/block/ll_rw_blk.c	2004-12-01 09:13:57 +01:00
+++ edited/drivers/block/ll_rw_blk.c	2004-12-03 13:34:28 +01:00
@@ -1257,11 +1257,7 @@
 	if (!blk_remove_plug(q))
 		return;
 
-	/*
-	 * was plugged, fire request_fn if queue has stuff to do
-	 */
-	if (elv_next_request(q))
-		q->request_fn(q);
+	q->request_fn(q);
 }
 EXPORT_SYMBOL(__generic_unplug_device);
 
@@ -2152,7 +2148,6 @@
 		return;
 
 	req->rq_status = RQ_INACTIVE;
-	req->q = NULL;
 	req->rl = NULL;
 
 	/*
@@ -2502,6 +2497,7 @@
 {
 	struct request_list *rl = &q->rq;
 	struct request *rq;
+	int requeued = 0;
 
 	spin_lock_irq(q->queue_lock);
 	clear_bit(QUEUE_FLAG_DRAIN, &q->queue_flags);
@@ -2510,8 +2506,12 @@
 		rq = list_entry_rq(q->drain_list.next);
 
 		list_del_init(&rq->queuelist);
-		__elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 1);
+		elv_requeue_request(q, rq);
+		requeued++;
 	}
+
+	if (requeued)
+		q->request_fn(q);
 
 	spin_unlock_irq(q->queue_lock);
 


-- 
Jens Axboe

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