[PATCH] CFQ scheduler, #2

[PATCH] CFQ scheduler, #2

[Jens Axboe]

Hi,

The version posted the other day did fair queueing of requests between
processes, but it did not help to provide fair request allocation. This
version does that too, results are rather remarkable. In addition, the
following changes were made:

- Fix lost request problem with rbtree aliasing. The default io
  scheduler in 2.5.60 has the same bug, a fix has been sent separetely
  to Linus that addresses this.

- Add front merging.

- Missing queue_lock grab in get_request_wait() before checking request
  list count. Again, a generic kernel bug. A patch will be sent to Linus
  to address that as well.

Obligatory contest results.

no_load:
Kernel         [runs]   Time    CPU%    Loads   LCPU%   Ratio
2.5.60              2   31      177.4   0       0.0     1.00
2.5.60-cfq-fr2      1   31      177.4   0       0.0     1.00
2.5.60-mm1          2   32      171.9   0       0.0     1.00
cacherun:
Kernel         [runs]   Time    CPU%    Loads   LCPU%   Ratio
2.5.60              2   29      182.8   0       0.0     0.94
2.5.60-cfq-fr2      1   29      182.8   0       0.0     0.94
2.5.60-mm1          2   29      186.2   0       0.0     0.91
process_load:
Kernel         [runs]   Time    CPU%    Loads   LCPU%   Ratio
2.5.60              2   38      142.1   12      47.4    1.23
2.5.60-cfq-fr2      1   43      123.3   20      67.4    1.39
2.5.60-mm1          2   38      142.1   13      50.0    1.19
ctar_load:
Kernel         [runs]   Time    CPU%    Loads   LCPU%   Ratio
2.5.60              2   38      147.4   0       0.0     1.23
2.5.60-cfq-fr2      1   37      151.4   0       0.0     1.19
2.5.60-mm1          2   36      155.6   0       0.0     1.12
xtar_load:
Kernel         [runs]   Time    CPU%    Loads   LCPU%   Ratio
2.5.60              2   40      140.0   0       2.5     1.29
2.5.60-cfq-fr2      1   37      148.6   0       2.6     1.19
2.5.60-mm1          2   39      143.6   0       2.6     1.22
io_load:
Kernel         [runs]   Time    CPU%    Loads   LCPU%   Ratio
2.5.60              2   93      61.3    2       14.0    3.00
2.5.60-cfq-fr2      1   73      76.7    1       9.8     2.35
2.5.60-mm1          2   82      69.5    1       9.8     2.56
read_load:
Kernel         [runs]   Time    CPU%    Loads   LCPU%   Ratio
2.5.60              2   40      140.0   0       5.0     1.29
2.5.60-cfq-fr2      1   40      140.0   0       5.0     1.29
2.5.60-mm1          2   38      147.4   0       2.6     1.19
list_load:
Kernel         [runs]   Time    CPU%    Loads   LCPU%   Ratio
2.5.60              2   35      157.1   0       8.6     1.13
2.5.60-cfq-fr2      1   35      160.0   0       11.4    1.13
2.5.60-mm1          2   34      164.7   0       8.8     1.06
mem_load:
Kernel         [runs]   Time    CPU%    Loads   LCPU%   Ratio
2.5.60              2   50      116.0   75      10.0    1.61
2.5.60-cfq-fr2      1   57      100.0   81      8.8     1.84
2.5.60-mm1          2   52      113.5   77      9.4     1.62
dbench_load:
Kernel         [runs]   Time    CPU%    Loads   LCPU%   Ratio
2.5.60              2   36      155.6   12693   27.8    1.16
2.5.60-mm1          2   35      160.0   12486   28.6    1.09


Patch is against 2.5.60-BK.

===== drivers/block/Makefile 1.14 vs edited =====
--- 1.14/drivers/block/Makefile	Mon Feb  3 23:19:36 2003
+++ edited/drivers/block/Makefile	Tue Feb 11 09:35:55 2003
@@ -8,7 +8,8 @@
 # In the future, some of these should be built conditionally.
 #
 
-obj-y	:= elevator.o ll_rw_blk.o ioctl.o genhd.o scsi_ioctl.o deadline-iosched.o
+obj-y	:= elevator.o ll_rw_blk.o ioctl.o genhd.o scsi_ioctl.o \
+	    deadline-iosched.o cfq-iosched.o
 
 obj-$(CONFIG_MAC_FLOPPY)	+= swim3.o
 obj-$(CONFIG_BLK_DEV_FD)	+= floppy.o
===== drivers/block/elevator.c 1.37 vs edited =====
--- 1.37/drivers/block/elevator.c	Tue Jan 14 23:59:43 2003
+++ edited/drivers/block/elevator.c	Fri Feb 14 14:08:15 2003
@@ -408,6 +408,16 @@
 	return NULL;
 }
 
+int elv_may_queue(request_queue_t *q, int rw)
+{
+	elevator_t *e = &q->elevator;
+
+	if (e->elevator_may_queue_fn)
+		return e->elevator_may_queue_fn(q, rw);
+
+	return 1;
+}
+
 int elv_register_queue(struct gendisk *disk)
 {
 	request_queue_t *q = disk->queue;
===== drivers/block/ll_rw_blk.c 1.151 vs edited =====
--- 1.151/drivers/block/ll_rw_blk.c	Thu Feb 13 05:02:43 2003
+++ edited/drivers/block/ll_rw_blk.c	Fri Feb 14 14:56:45 2003
@@ -45,7 +45,7 @@
  * Number of requests per queue.  This many for reads and for writes (twice
  * this number, total).
  */
-static int queue_nr_requests;
+int queue_nr_requests;
 
 /*
  * How many free requests must be available before we wake a process which
@@ -1283,7 +1283,7 @@
 	if (blk_init_free_list(q))
 		return -ENOMEM;
 
-	if ((ret = elevator_init(q, &iosched_deadline))) {
+	if ((ret = elevator_init(q, &iosched_cfq))) {
 		blk_cleanup_queue(q);
 		return ret;
 	}
@@ -1320,7 +1320,7 @@
 	struct request *rq = NULL;
 	struct request_list *rl = q->rq + rw;
 
-	if (!list_empty(&rl->free)) {
+	if (!list_empty(&rl->free) && elv_may_queue(q, rw)) {
 		rq = blkdev_free_rq(&rl->free);
 		list_del_init(&rq->queuelist);
 		rq->ref_count = 1;
@@ -1358,11 +1358,19 @@
 
 	generic_unplug_device(q);
 	do {
+		int block = 0;
+
 		prepare_to_wait_exclusive(&rl->wait, &wait,
 					TASK_UNINTERRUPTIBLE);
-		if (!rl->count)
+		spin_lock_irq(q->queue_lock);
+		if (!rl->count || !elv_may_queue(q, rw))
+			block = 1;
+		spin_unlock_irq(q->queue_lock);
+
+		if (block)
 			io_schedule();
 		finish_wait(&rl->wait, &wait);
+
 		spin_lock_irq(q->queue_lock);
 		rq = get_request(q, rw);
 		spin_unlock_irq(q->queue_lock);
===== include/linux/elevator.h 1.18 vs edited =====
--- 1.18/include/linux/elevator.h	Sun Jan 12 15:10:40 2003
+++ edited/include/linux/elevator.h	Fri Feb 14 14:07:45 2003
@@ -15,6 +15,7 @@
 typedef void (elevator_remove_req_fn) (request_queue_t *, struct request *);
 typedef struct request *(elevator_request_list_fn) (request_queue_t *, struct request *);
 typedef struct list_head *(elevator_get_sort_head_fn) (request_queue_t *, struct request *);
+typedef int (elevator_may_queue_fn) (request_queue_t *, int);
 
 typedef int (elevator_init_fn) (request_queue_t *, elevator_t *);
 typedef void (elevator_exit_fn) (request_queue_t *, elevator_t *);
@@ -34,6 +35,8 @@
 	elevator_request_list_fn *elevator_former_req_fn;
 	elevator_request_list_fn *elevator_latter_req_fn;
 
+	elevator_may_queue_fn *elevator_may_queue_fn;
+
 	elevator_init_fn *elevator_init_fn;
 	elevator_exit_fn *elevator_exit_fn;
 
@@ -58,6 +61,7 @@
 extern struct request *elv_latter_request(request_queue_t *, struct request *);
 extern int elv_register_queue(struct gendisk *);
 extern void elv_unregister_queue(struct gendisk *);
+extern int elv_may_queue(request_queue_t *, int);
 
 #define __elv_add_request_pos(q, rq, pos)	\
 	(q)->elevator.elevator_add_req_fn((q), (rq), (pos))
@@ -72,6 +76,8 @@
  * starvation
  */
 extern elevator_t iosched_deadline;
+
+extern elevator_t iosched_cfq;
 
 extern int elevator_init(request_queue_t *, elevator_t *);
 extern void elevator_exit(request_queue_t *);
--- /dev/null	2003-01-19 21:08:59.000000000 +0100
+++ linux-2.5-sfq/drivers/block/cfq-iosched.c	2003-02-14 15:06:05.000000000 +0100
@@ -0,0 +1,699 @@
+/*
+ *  linux/drivers/block/cfq-iosched.c
+ *
+ *  CFQ, or complete fairness queueing, disk scheduler.
+ *
+ *  Based on ideas from a previously unfinished io
+ *  scheduler (round robin per-process disk scheduling) and Andrea Arcangeli.
+ *
+ *  Copyright (C) 2003 Jens Axboe <axboe@suse.de>
+ */
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/blkdev.h>
+#include <linux/elevator.h>
+#include <linux/bio.h>
+#include <linux/blk.h>
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/compiler.h>
+#include <linux/hash.h>
+#include <linux/rbtree.h>
+#include <linux/mempool.h>
+
+/*
+ * tunables
+ */
+static int cfq_quantum = 4;
+static int cfq_queued = 8;
+
+#define CFQ_QHASH_SHIFT		6
+#define CFQ_QHASH_ENTRIES	(1 << CFQ_QHASH_SHIFT)
+#define list_entry_qhash(entry)	list_entry((entry), struct cfq_queue, cfq_hash)
+
+#define CFQ_MHASH_SHIFT		8
+#define CFQ_MHASH_BLOCK(sec)	((sec) >> 3)
+#define CFQ_MHASH_ENTRIES	(1 << CFQ_MHASH_SHIFT)
+#define CFQ_MHASH_FN(sec)	(hash_long(CFQ_MHASH_BLOCK((sec)),CFQ_MHASH_SHIFT))
+#define ON_MHASH(crq)		!list_empty(&(crq)->hash)
+#define rq_hash_key(rq)		((rq)->sector + (rq)->nr_sectors)
+#define list_entry_hash(ptr)	list_entry((ptr), struct cfq_rq, hash)
+
+#define list_entry_cfqq(ptr)	list_entry((ptr), struct cfq_queue, cfq_list)
+
+#define RQ_DATA(rq)		((struct cfq_rq *) (rq)->elevator_private)
+
+static kmem_cache_t *crq_pool;
+static kmem_cache_t *cfq_pool;
+static mempool_t *cfq_mpool;
+
+struct cfq_queue {
+	struct list_head cfq_hash;
+	struct list_head cfq_list;
+	struct rb_root sort_list;
+	int pid;
+	int queued[2];
+#if 0
+	/*
+	 * with a simple addition like this, we can do io priorities. almost.
+	 * does need a split request free list, too.
+	 */
+	int io_prio
+#endif
+};
+
+struct cfq_data {
+	struct list_head rr_list;
+	struct list_head *dispatch;
+	struct list_head *cfq_hash;
+
+	struct list_head *crq_hash;
+
+	int busy_queues;
+
+	unsigned long random_seed;
+};
+
+struct cfq_rq {
+	struct rb_node rb_node;
+	sector_t rb_key;
+
+	struct request *request;
+
+	struct cfq_queue *cfq_queue;
+
+	struct list_head hash;
+};
+
+static void cfq_put_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq);
+static struct cfq_queue *cfq_find_cfq_hash(struct cfq_data *cfqd, int pid);
+static void cfq_dispatch_sort(struct list_head *head, struct cfq_rq *crq);
+
+/*
+ * lots of deadline iosched dupes, can be abstracted later...
+ */
+static inline void __cfq_del_crq_hash(struct cfq_rq *crq)
+{
+	list_del_init(&crq->hash);
+}
+
+static inline void cfq_del_crq_hash(struct cfq_rq *crq)
+{
+	if (ON_MHASH(crq))
+		__cfq_del_crq_hash(crq);
+}
+
+static inline void cfq_add_crq_hash(struct cfq_data *cfqd, struct cfq_rq *crq)
+{
+	struct request *rq = crq->request;
+
+	BUG_ON(ON_MHASH(crq));
+
+	list_add(&crq->hash, &cfqd->crq_hash[CFQ_MHASH_FN(rq_hash_key(rq))]);
+}
+
+static struct request *cfq_find_rq_hash(struct cfq_data *cfqd, sector_t offset)
+{
+	struct list_head *hash_list = &cfqd->crq_hash[CFQ_MHASH_FN(offset)];
+	struct list_head *entry, *next = hash_list->next;
+
+	while ((entry = next) != hash_list) {
+		struct cfq_rq *crq = list_entry_hash(entry);
+		struct request *__rq = crq->request;
+
+		next = entry->next;
+		
+		BUG_ON(!ON_MHASH(crq));
+
+		if (!rq_mergeable(__rq)) {
+			__cfq_del_crq_hash(crq);
+			continue;
+		}
+
+		if (rq_hash_key(__rq) == offset)
+			return __rq;
+	}
+
+	return NULL;
+}
+
+/*
+ * rb tree support functions
+ */
+#define RB_EMPTY(root)	((root)->rb_node == NULL)
+#define RB_CLEAR(root)	((root)->rb_node = NULL)
+#define ON_RB(crq)	((crq)->cfq_queue != NULL)
+#define rb_entry_crq(node)	rb_entry((node), struct cfq_rq, rb_node)
+#define rq_rb_key(rq)		(rq)->sector
+
+static inline void cfq_del_crq_rb(struct cfq_queue *cfqq, struct cfq_rq *crq)
+{
+	if (ON_RB(crq)) {
+		rb_erase(&crq->rb_node, &cfqq->sort_list);
+		crq->cfq_queue = NULL;
+	}
+}
+
+static struct cfq_rq *
+__cfq_add_crq_rb(struct cfq_queue *cfqq, struct cfq_rq *crq)
+{
+	struct rb_node **p = &cfqq->sort_list.rb_node;
+	struct rb_node *parent = NULL;
+	struct cfq_rq *__crq;
+
+	while (*p) {
+		parent = *p;
+		__crq = rb_entry_crq(parent);
+
+		if (crq->rb_key < __crq->rb_key)
+			p = &(*p)->rb_left;
+		else if (crq->rb_key > __crq->rb_key)
+			p = &(*p)->rb_right;
+		else
+			return __crq;
+	}
+
+	rb_link_node(&crq->rb_node, parent, p);
+	return 0;
+}
+
+static void
+cfq_add_crq_rb(struct cfq_data *cfqd, struct cfq_queue *cfqq,struct cfq_rq *crq)
+{
+	struct request *rq = crq->request;
+	struct cfq_rq *__alias;
+
+	crq->rb_key = rq_rb_key(rq);
+
+retry:
+	__alias = __cfq_add_crq_rb(cfqq, crq);
+	if (!__alias) {
+		rb_insert_color(&crq->rb_node, &cfqq->sort_list);
+		crq->cfq_queue = cfqq;
+		cfqq->queued[rq_data_dir(rq)]++;
+		return;
+	}
+
+	cfq_del_crq_rb(cfqq, __alias);
+	cfq_dispatch_sort(cfqd->dispatch, __alias);
+	goto retry;
+}
+
+static struct request *
+cfq_find_rq_rb(struct cfq_data *cfqd, sector_t sector)
+{
+	struct cfq_queue *cfqq = cfq_find_cfq_hash(cfqd, current->pid);
+	struct rb_node *n;
+
+	if (!cfqq)
+		goto out;
+
+	n = cfqq->sort_list.rb_node;
+	while (n) {
+		struct cfq_rq *crq = rb_entry_crq(n);
+
+		if (sector < crq->rb_key)
+			n = n->rb_left;
+		else if (sector > crq->rb_key)
+			n = n->rb_right;
+		else
+			return crq->request;
+	}
+
+out:
+	return NULL;
+}
+
+static void cfq_remove_request(request_queue_t *q, struct request *rq)
+{
+	struct cfq_data *cfqd = q->elevator.elevator_data;
+	struct cfq_rq *crq = RQ_DATA(rq);
+
+	if (crq) {
+		struct cfq_queue *cfqq = crq->cfq_queue;
+
+		cfq_del_crq_hash(crq);
+
+		if (cfqq) {
+			cfq_del_crq_rb(cfqq, crq);
+
+			if (RB_EMPTY(&cfqq->sort_list))
+				cfq_put_queue(cfqd, cfqq);
+		}
+	}
+
+	if (&rq->queuelist == q->last_merge)
+		q->last_merge = NULL;
+
+	list_del_init(&rq->queuelist);
+}
+
+static int
+cfq_merge(request_queue_t *q, struct list_head **insert, struct bio *bio)
+{
+	struct cfq_data *cfqd = q->elevator.elevator_data;
+	struct request *__rq;
+	int ret;
+
+	ret = elv_try_last_merge(q, bio);
+	if (ret != ELEVATOR_NO_MERGE) {
+		__rq = list_entry_rq(q->last_merge);
+		goto out_insert;
+	}
+
+	__rq = cfq_find_rq_hash(cfqd, bio->bi_sector);
+	if (__rq) {
+		BUG_ON(__rq->sector + __rq->nr_sectors != bio->bi_sector);
+
+		if (elv_rq_merge_ok(__rq, bio)) {
+			ret = ELEVATOR_BACK_MERGE;
+			goto out;
+		}
+	}
+
+	__rq = cfq_find_rq_rb(cfqd, bio->bi_sector + bio_sectors(bio));
+	if (__rq) {
+		if (elv_rq_merge_ok(__rq, bio)) {
+			ret = ELEVATOR_FRONT_MERGE;
+			goto out;
+		}
+	}
+
+	return ELEVATOR_NO_MERGE;
+out:
+	q->last_merge = &__rq->queuelist;
+out_insert:
+	*insert = &__rq->queuelist;
+	return ret;
+}
+
+static void cfq_merged_request(request_queue_t *q, struct request *req)
+{
+	struct cfq_data *cfqd = q->elevator.elevator_data;
+	struct cfq_rq *crq = RQ_DATA(req);
+
+	cfq_del_crq_hash(crq);
+	cfq_add_crq_hash(cfqd, crq);
+
+	if (ON_RB(crq) && rq_rb_key(req) != crq->rb_key) {
+		struct cfq_queue *cfqq = crq->cfq_queue;
+
+		cfq_del_crq_rb(cfqq, crq);
+		cfq_add_crq_rb(cfqd, cfqq, crq);
+	}
+
+	q->last_merge = &req->queuelist;
+}
+
+static void
+cfq_merged_requests(request_queue_t *q, struct request *req,
+		    struct request *next)
+{
+	cfq_merged_request(q, req);
+	cfq_remove_request(q, next);
+}
+
+static void cfq_dispatch_sort(struct list_head *head, struct cfq_rq *crq)
+{
+	struct list_head *entry = head;
+	struct request *__rq;
+
+	if (!list_empty(head)) {
+		__rq = list_entry_rq(head->next);
+
+		if (crq->request->sector < __rq->sector) {
+			entry = head->prev;
+			goto link;
+		}
+	}
+
+	while ((entry = entry->prev) != head) {
+		__rq = list_entry_rq(entry);
+
+		if (crq->request->sector <= __rq->sector)
+			break;
+	}
+
+link:
+	list_add_tail(&crq->request->queuelist, entry);
+}
+
+static inline void
+__cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq)
+{
+	struct cfq_rq *crq;
+
+	crq = rb_entry_crq(rb_first(&cfqq->sort_list));
+
+	cfq_del_crq_rb(cfqq, crq);
+	cfq_dispatch_sort(cfqd->dispatch, crq);
+}
+
+static int cfq_dispatch_requests(struct cfq_data *cfqd)
+{
+	struct cfq_queue *cfqq;
+	struct list_head *entry, *tmp;
+	int ret, queued, good_queues;
+
+	if (list_empty(&cfqd->rr_list))
+		return 0;
+
+	queued = ret = 0;
+restart:
+	good_queues = 0;
+	list_for_each_safe(entry, tmp, &cfqd->rr_list) {
+		cfqq = list_entry_cfqq(cfqd->rr_list.next);
+
+		BUG_ON(RB_EMPTY(&cfqq->sort_list));
+
+		__cfq_dispatch_requests(cfqd, cfqq);
+
+		if (RB_EMPTY(&cfqq->sort_list))
+			cfq_put_queue(cfqd, cfqq);
+		else
+			good_queues++;
+
+		queued++;
+		ret = 1;
+	}
+
+	if ((queued < cfq_quantum) && good_queues)
+		goto restart;
+
+	return ret;
+}
+
+static struct request *cfq_next_request(request_queue_t *q)
+{
+	struct cfq_data *cfqd = q->elevator.elevator_data;
+	struct request *rq;
+
+	if (!list_empty(cfqd->dispatch)) {
+		struct cfq_rq *crq;
+dispatch:
+		rq = list_entry_rq(cfqd->dispatch->next);
+
+		if (q->last_merge == &rq->queuelist)
+			q->last_merge = NULL;
+
+		crq = RQ_DATA(rq);
+		if (crq)
+			cfq_del_crq_hash(crq);
+
+		return rq;
+	}
+
+	if (cfq_dispatch_requests(cfqd))
+		goto dispatch;
+
+	return NULL;
+}
+
+static inline struct cfq_queue *
+__cfq_find_cfq_hash(struct cfq_data *cfqd, int pid, const int hashval)
+{
+	struct list_head *hash_list = &cfqd->cfq_hash[hashval];
+	struct list_head *entry;
+
+	list_for_each(entry, hash_list) {
+		struct cfq_queue *__cfqq = list_entry_qhash(entry);
+
+		if (__cfqq->pid == pid)
+			return __cfqq;
+	}
+
+	return NULL;
+}
+
+static struct cfq_queue *cfq_find_cfq_hash(struct cfq_data *cfqd, int pid)
+{
+	const int hashval = hash_long(current->pid, CFQ_QHASH_SHIFT);
+
+	return __cfq_find_cfq_hash(cfqd, pid, hashval);
+}
+
+static void cfq_put_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
+{
+	cfqd->busy_queues--;
+	list_del(&cfqq->cfq_list);
+	list_del(&cfqq->cfq_hash);
+	mempool_free(cfqq, cfq_mpool);
+}
+
+static struct cfq_queue *cfq_get_queue(struct cfq_data *cfqd, int pid)
+{
+	const int hashval = hash_long(current->pid, CFQ_QHASH_SHIFT);
+	struct cfq_queue *cfqq = __cfq_find_cfq_hash(cfqd, pid, hashval);
+
+	if (!cfqq) {
+		cfqq = mempool_alloc(cfq_mpool, GFP_NOIO);
+
+		INIT_LIST_HEAD(&cfqq->cfq_hash);
+		INIT_LIST_HEAD(&cfqq->cfq_list);
+		RB_CLEAR(&cfqq->sort_list);
+
+		cfqq->pid = pid;
+		cfqq->queued[0] = cfqq->queued[1] = 0;
+		list_add(&cfqq->cfq_hash, &cfqd->cfq_hash[hashval]);
+	}
+
+	return cfqq;
+}
+
+static void cfq_enqueue(struct cfq_data *cfqd, struct cfq_rq *crq)
+{
+	struct cfq_queue *cfqq;
+
+	cfqq = cfq_get_queue(cfqd, current->pid);
+
+	cfq_add_crq_rb(cfqd, cfqq, crq);
+
+	if (list_empty(&cfqq->cfq_list)) {
+		list_add(&cfqq->cfq_list, &cfqd->rr_list);
+		cfqd->busy_queues++;
+	}
+}
+
+static void
+cfq_insert_request(request_queue_t *q, struct request *rq,
+		   struct list_head *insert_here)
+{
+	struct cfq_data *cfqd = q->elevator.elevator_data;
+	struct cfq_rq *crq = RQ_DATA(rq);
+
+	if (unlikely(!blk_fs_request(rq))) {
+		if (!insert_here)
+			insert_here = cfqd->dispatch->prev;
+
+		list_add(&rq->queuelist, insert_here);
+		return;
+	}
+
+	if (rq_mergeable(rq)) {
+		cfq_add_crq_hash(cfqd, crq);
+
+		if (!q->last_merge)
+			q->last_merge = &rq->queuelist;
+	}
+
+	cfq_enqueue(cfqd, crq);
+}
+
+static int cfq_queue_empty(request_queue_t *q)
+{
+	struct cfq_data *cfqd = q->elevator.elevator_data;
+
+	if (list_empty(cfqd->dispatch) && list_empty(&cfqd->rr_list))
+		return 1;
+
+	return 0;
+}
+
+static struct request *
+cfq_former_request(request_queue_t *q, struct request *rq)
+{
+	struct cfq_rq *crq = RQ_DATA(rq);
+	struct rb_node *rbprev = rb_prev(&crq->rb_node);
+
+	if (rbprev)
+		return rb_entry_crq(rbprev)->request;
+
+	return NULL;
+}
+
+static struct request *
+cfq_latter_request(request_queue_t *q, struct request *rq)
+{
+	struct cfq_rq *crq = RQ_DATA(rq);
+	struct rb_node *rbnext = rb_next(&crq->rb_node);
+
+	if (rbnext)
+		return rb_entry_crq(rbnext)->request;
+
+	return NULL;
+}
+
+extern int queue_nr_requests;
+
+static int cfq_may_queue(request_queue_t *q, int rw)
+{
+	struct cfq_data *cfqd = q->elevator.elevator_data;
+	struct cfq_queue *cfqq;
+	int limit, ret = 1;
+
+	if (!cfqd->busy_queues)
+		goto out;
+
+	cfqq = cfq_find_cfq_hash(cfqd, current->pid);
+	if (!cfqq)
+		goto out;
+
+	if (cfqq->queued[rw] < cfq_queued)
+		goto out;
+
+	limit = (queue_nr_requests - cfq_queued) / cfqd->busy_queues;
+	if (cfqq->queued[rw] > limit)
+		ret = 0;
+
+out:
+	return ret;
+}
+
+static void cfq_exit(request_queue_t *q, elevator_t *e)
+{
+	struct cfq_data *cfqd = e->elevator_data;
+	struct cfq_rq *crq;
+	struct request *rq;
+	int i;
+
+	for (i = READ; i <= WRITE; i++) {
+		struct request_list *rl = &q->rq[i];
+		struct list_head *entry;
+
+		list_for_each(entry, &rl->free) {
+			rq = list_entry_rq(entry);
+
+			crq = RQ_DATA(rq);
+			if (!crq)
+				continue;
+
+			rq->elevator_private = NULL;
+			kmem_cache_free(crq_pool, crq);
+		}
+	}
+
+	e->elevator_data = NULL;
+	kfree(cfqd->crq_hash);
+	kfree(cfqd->cfq_hash);
+	kfree(cfqd);
+}
+
+static void *slab_pool_alloc(int gfp_mask, void *data)
+{
+	return kmem_cache_alloc(data, gfp_mask);
+}
+
+static void slab_pool_free(void *ptr, void *data)
+{
+	kmem_cache_free(data, ptr);
+}
+
+static int cfq_init(request_queue_t *q, elevator_t *e)
+{
+	struct cfq_data *cfqd;
+	struct request *rq;
+	struct cfq_rq *crq;
+	int i, ret = 0;
+
+	cfqd = kmalloc(sizeof(*cfqd), GFP_KERNEL);
+	if (!cfqd)
+		return -ENOMEM;
+
+	memset(cfqd, 0, sizeof(*cfqd));
+	INIT_LIST_HEAD(&cfqd->rr_list);
+
+	cfqd->crq_hash = kmalloc(sizeof(struct list_head) * CFQ_MHASH_ENTRIES, GFP_KERNEL);
+	if (!cfqd->crq_hash)
+		goto out_crqhash;
+
+	cfqd->cfq_hash = kmalloc(sizeof(struct list_head) * CFQ_QHASH_ENTRIES, GFP_KERNEL);
+	if (!cfqd->cfq_hash)
+		goto out_cfqhash;
+
+	for (i = 0; i < CFQ_MHASH_ENTRIES; i++)
+		INIT_LIST_HEAD(&cfqd->crq_hash[i]);
+	for (i = 0; i < CFQ_QHASH_ENTRIES; i++)
+		INIT_LIST_HEAD(&cfqd->cfq_hash[i]);
+
+	for (i = READ; i <= WRITE; i++) {
+		struct request_list *rl = &q->rq[i];
+		struct list_head *entry;
+
+		list_for_each(entry, &rl->free) {
+			rq = list_entry_rq(entry);
+
+			crq = kmem_cache_alloc(crq_pool, GFP_KERNEL);
+			if (!crq) {
+				ret = -ENOMEM;
+				break;
+			}
+
+			memset(crq, 0, sizeof(*crq));
+			INIT_LIST_HEAD(&crq->hash);
+			crq->request = rq;
+			rq->elevator_private = crq;
+		}
+	}
+
+	cfqd->dispatch = &q->queue_head;
+	e->elevator_data = cfqd;
+	return ret;
+out_cfqhash:
+	kfree(cfqd->crq_hash);
+out_crqhash:
+	kfree(cfqd);
+	return -ENOMEM;
+}
+
+static int __init cfq_slab_setup(void)
+{
+	crq_pool = kmem_cache_create("crq_pool", sizeof(struct cfq_rq), 0, 0,
+					NULL, NULL);
+
+	if (!crq_pool)
+		panic("cfq_iosched: can't init crq pool\n");
+
+	cfq_pool = kmem_cache_create("cfq_pool", sizeof(struct cfq_queue), 0, 0,
+					NULL, NULL);
+
+	if (!cfq_pool)
+		panic("cfq_iosched: can't init cfq pool\n");
+
+	cfq_mpool = mempool_create(64, slab_pool_alloc, slab_pool_free, cfq_pool);
+
+	if (!cfq_mpool)
+		panic("cfq_iosched: can't init cfq mpool\n");
+
+	return 0;
+}
+
+subsys_initcall(cfq_slab_setup);
+
+elevator_t iosched_cfq = {
+	.elevator_merge_fn = 		cfq_merge,
+	.elevator_merged_fn =		cfq_merged_request,
+	.elevator_merge_req_fn =	cfq_merged_requests,
+	.elevator_next_req_fn =		cfq_next_request,
+	.elevator_add_req_fn =		cfq_insert_request,
+	.elevator_remove_req_fn =	cfq_remove_request,
+	.elevator_queue_empty_fn =	cfq_queue_empty,
+	.elevator_former_req_fn =	cfq_former_request,
+	.elevator_latter_req_fn =	cfq_latter_request,
+	.elevator_may_queue_fn =	cfq_may_queue,
+	.elevator_init_fn =		cfq_init,
+	.elevator_exit_fn =		cfq_exit,
+};
+
+EXPORT_SYMBOL(iosched_cfq);

-- 
Jens Axboe

Re: [PATCH] CFQ scheduler, #2

[Jens Axboe]

On Fri, Feb 14 2003, Jens Axboe wrote:
> Obligatory contest results.

Agrh, old scores (not the fr2). Here's for the version sent out:

no_load:
Kernel        [runs]    Time    CPU%    Loads   LCPU%   Ratio
2.5.60             2    31      177.4   0       0.0     1.00
2.5.60-cfq-fr      2    31      177.4   0       0.0     1.00
2.5.60-mm1         2    32      171.9   0       0.0     1.00
cacherun:
Kernel        [runs]    Time    CPU%    Loads   LCPU%   Ratio
2.5.60             2    29      182.8   0       0.0     0.94
2.5.60-cfq-fr      2    29      182.8   0       0.0     0.94
2.5.60-mm1         2    29      186.2   0       0.0     0.91
process_load:
Kernel        [runs]    Time    CPU%    Loads   LCPU%   Ratio
2.5.60             2    38      142.1   12      47.4    1.23
2.5.60-cfq-fr      2    38      142.1   12      47.4    1.23
2.5.60-mm1         2    38      142.1   13      50.0    1.19
ctar_load:
Kernel        [runs]    Time    CPU%    Loads   LCPU%   Ratio
2.5.60             2    38      147.4   0       0.0     1.23
2.5.60-cfq-fr      2    38      147.4   0       0.0     1.23
2.5.60-mm1         2    36      155.6   0       0.0     1.12
xtar_load:
Kernel        [runs]    Time    CPU%    Loads   LCPU%   Ratio
2.5.60             2    40      140.0   0       2.5     1.29
2.5.60-cfq-fr      2    38      147.4   0       2.6     1.23
2.5.60-mm1         2    39      143.6   0       2.6     1.22
io_load:
Kernel        [runs]    Time    CPU%    Loads   LCPU%   Ratio
2.5.60             2    93      61.3    2       14.0    3.00
2.5.60-cfq-fr      2    71      78.9    1       8.1     2.29
2.5.60-mm1         2    82      69.5    1       9.8     2.56
read_load:
Kernel        [runs]    Time    CPU%    Loads   LCPU%   Ratio
2.5.60             2    40      140.0   0       5.0     1.29
2.5.60-cfq-fr      2    41      136.6   0       4.9     1.32
2.5.60-mm1         2    38      147.4   0       2.6     1.19
list_load:
Kernel        [runs]    Time    CPU%    Loads   LCPU%   Ratio
2.5.60             2    35      157.1   0       8.6     1.13
2.5.60-cfq-fr      2    34      161.8   0       8.8     1.10
2.5.60-mm1         2    34      164.7   0       8.8     1.06
mem_load:
Kernel        [runs]    Time    CPU%    Loads   LCPU%   Ratio
2.5.60             2    50      116.0   75      10.0    1.61
2.5.60-cfq-fr      2    47      123.4   74      10.6    1.52
2.5.60-mm1         2    52      113.5   77      9.4     1.62
dbench_load:
Kernel        [runs]    Time    CPU%    Loads   LCPU%   Ratio
2.5.60             2    36      155.6   12693   27.8    1.16
2.5.60-cfq-fr      2    35      157.1   11368   25.7    1.13
2.5.60-mm1         2    35      160.0   12486   28.6    1.09

-- 
Jens Axboe

Re: [PATCH] CFQ scheduler, #2

[Ed Tomlinson]

Jens Axboe wrote:
 
> The version posted the other day did fair queueing of requests between
> processes, but it did not help to provide fair request allocation. This
> version does that too, results are rather remarkable. In addition, the
> following changes were made:

The numbers from the second message are nice - especially considering this
is only the second iteration...

A question about io priorities.  I wonder if they could not be implemented
via a per pid cfq_quantum?  If I am not missunderstanding things, a bigger
value here for a given process should mean that it gets a larger share of 
the io bandwidth...

Comments?
Ed Tomlinson

Re: [PATCH] CFQ scheduler, #2

[Jens Axboe]

On Fri, Feb 14 2003, Ed Tomlinson wrote:
> Jens Axboe wrote:
>  
> > The version posted the other day did fair queueing of requests between
> > processes, but it did not help to provide fair request allocation. This
> > version does that too, results are rather remarkable. In addition, the
> > following changes were made:
> 
> The numbers from the second message are nice - especially considering this
> is only the second iteration...
> 
> A question about io priorities.  I wonder if they could not be implemented
> via a per pid cfq_quantum?  If I am not missunderstanding things, a bigger
> value here for a given process should mean that it gets a larger share of 
> the io bandwidth...

That's exactly right, and yes that would be one way of doing it.

-- 
Jens Axboe

Re: [PATCH] CFQ scheduler, #2

[Mike Galbraith]

[-- Attachment #1: Type: text/plain, Size: 858 bytes --]

At 03:19 PM 2/14/2003 +0100, Jens Axboe wrote:
>Hi,

Greetings

>The version posted the other day did fair queueing of requests between
>processes, but it did not help to provide fair request allocation. This
>version does that too, results are rather remarkable. In addition, the
>following changes were made:
>
>- Fix lost request problem with rbtree aliasing. The default io
>   scheduler in 2.5.60 has the same bug, a fix has been sent separetely
>   to Linus that addresses this.
>
>- Add front merging.
>
>- Missing queue_lock grab in get_request_wait() before checking request
>   list count. Again, a generic kernel bug. A patch will be sent to Linus
>   to address that as well.

I gave this a burn, and under hefty load it seems to provide a bit of 
anti-thrash benefit.

i(dang, wish I had pine/vi for winders box)log data attached

         -Mike

[-- Attachment #2: xx.txt --]
[-- Type: text/plain, Size: 1645 bytes --]

2.5.61virgin make bzImage reference run
(poor box isn't _rediculously_ overloaded;)
real    8m9.710s
user    7m27.045s
sys     0m34.605s

three consecutive make -j30 bzImage runs

2.5.61cfq2
real    8m41.834s   8m36.908s   8m38.164s
user    7m37.208s   7m36.986s   7m36.456s
sys     0m42.921s   0m43.387s   0m43.312s

2.5.61virgin
real    8m39.723s   8m39.456s   8m42.102s
user    7m39.343s   7m38.800s   7m38.542s
sys     0m43.417s   0m43.322s   0m43.502s

/proc/vmstat    2.5.61cfq2   2.5.61virgin
-----------------------------------------
nr_dirty                20             13
nr_writeback             0              0
nr_pagecache          7308           7593
nr_page_table_pages     85             85
nr_reverse_maps       3229           3198
nr_mapped              599            599
nr_slab               1203           1184
pgpgin             1767432        1911614
pgpgout            1606743        1746497
pswpin              311297         338436
pswpout             371161         406675
pgalloc            3037961        3070811
pgfree             3060825        3093420
pgactivate          142329         135616
pgdeactivate        514672         507026
pgfault            4896877        4928530
pgmajfault           74342          84476
pgscan             2751953        5328260  <== ? hmm
pgrefill           1821561        1972715
pgsteal             528014         575301
pginodesteal             0              0
kswapd_steal        380282         522126
kswapd_inodesteal     7010           7132
pageoutrun            1107           1956
allocstall            3472           1238
pgrotated           358243         413450

Re: [PATCH] CFQ scheduler, #2

[Rik van Riel]

On Sat, 15 Feb 2003, Mike Galbraith wrote:

> I gave this a burn, and under hefty load it seems to provide a bit of
> anti-thrash benefit.

Judging from your log, it ends up stalling kswapd and
dramatically increases the number of times that normal
processes need to go into the pageout code.

If this provides an anti-thrashing benefit, something's
wrong with the VM in 2.5 ;)

Rik
-- 
Bravely reimplemented by the knights who say "NIH".
http://www.surriel.com/		http://guru.conectiva.com/
Current spamtrap:  <a href=mailto:"october@surriel.com">october@surriel.com</a>

Re: [PATCH] CFQ scheduler, #2

[Mike Galbraith]

At 09:22 AM 2/15/2003 -0200, Rik van Riel wrote:
>On Sat, 15 Feb 2003, Mike Galbraith wrote:
>
>>I gave this a burn, and under hefty load it seems to provide a bit of
>>anti-thrash benefit.
>
>Judging from your log, it ends up stalling kswapd and
>dramatically increases the number of times that normal
>processes need to go into the pageout code.
>
>If this provides an anti-thrashing benefit, something's
>wrong with the VM in 2.5 ;)

Which number are you looking at?

         -Mike

Re: [PATCH] CFQ scheduler, #2

[Rik van Riel]

On Sat, 15 Feb 2003, Mike Galbraith wrote:

> >Judging from your log, it ends up stalling kswapd and
> >dramatically increases the number of times that normal
> >processes need to go into the pageout code.
> >
> >If this provides an anti-thrashing benefit, something's
> >wrong with the VM in 2.5 ;)
>
> Which number are you looking at?

pgscan             2751953        5328260  <== ? hmm

kswapd_steal        380282         522126
pageoutrun            1107           1956
allocstall            3472           1238

- we scan far less pages
- kswapd reclaims less pages
- we go into the pageout code less often
- allocations stall more often for a lack of free memory

cheers,

Rik
-- 
Bravely reimplemented by the knights who say "NIH".
http://www.surriel.com/		http://guru.conectiva.com/
Current spamtrap:  <a href=mailto:"october@surriel.com">october@surriel.com</a>

Re: [PATCH] CFQ scheduler, #2

[William Lee Irwin III]

On Sat, Feb 15, 2003 at 09:49:15AM -0200, Rik van Riel wrote:
> pgscan             2751953        5328260  <== ? hmm
> kswapd_steal        380282         522126
> pageoutrun            1107           1956
> allocstall            3472           1238

$ echo $(( 5328260/1956.0 ))       
2724.0593047034763
$ echo $(( (5328260/1956.0)*4 ))
10896.237218813905

That's 2724 pages or 11MB scanned per pageout run. Order-of-magnitude
better ratio for pages stolen per pageout run. Wouldn't mind seeing a
patch that improves this.


-- wli

Re: [PATCH] CFQ scheduler, #2

[Mike Galbraith]

At 09:49 AM 2/15/2003 -0200, Rik van Riel wrote:
>On Sat, 15 Feb 2003, Mike Galbraith wrote:
>
> > >Judging from your log, it ends up stalling kswapd and
> > >dramatically increases the number of times that normal
> > >processes need to go into the pageout code.
> > >
> > >If this provides an anti-thrashing benefit, something's
> > >wrong with the VM in 2.5 ;)
> >
> > Which number are you looking at?
>
>pgscan             2751953        5328260  <== ? hmm
>
>kswapd_steal        380282         522126
>pageoutrun            1107           1956
>allocstall            3472           1238
>
>- we scan far less pages
>- kswapd reclaims less pages
>- we go into the pageout code less often
>- allocations stall more often for a lack of free memory

I would interpret that differently.  I would say we scan less because we 
don't need to scan as much, kswapd reclaims less for the same reason, and 
ditto for pageout ;-)  The reduction in scans does seem _way_ high though...

wrt allocstall, I bet if I do a few runs, I'll see mucho variance there 
(could be wrong.. hunch)

         -Mke

Re: [PATCH] CFQ scheduler, #2

[Mike Galbraith]

At 01:07 PM 2/15/2003 +0100, Rik van Riel wrote:
>At 09:49 AM 2/15/2003 -0200, Rik van Riel wrote:
>>On Sat, 15 Feb 2003, Mike Galbraith wrote:
>>
>> > >Judging from your log, it ends up stalling kswapd and
>> > >dramatically increases the number of times that normal
>> > >processes need to go into the pageout code.
>> > >
>> > >If this provides an anti-thrashing benefit, something's
>> > >wrong with the VM in 2.5 ;)
>> >
>> > Which number are you looking at?
>>
>>pgscan             2751953        5328260  <== ? hmm
>>
>>kswapd_steal        380282         522126
>>pageoutrun            1107           1956
>>allocstall            3472           1238
>>
>>- we scan far less pages
>>- kswapd reclaims less pages
>>- we go into the pageout code less often
>>- allocations stall more often for a lack of free memory
>
>I would interpret that differently.  I would say we scan less because we 
>don't need to scan as much, kswapd reclaims less for the same reason, and 
>ditto for pageout ;-)  The reduction in scans does seem _way_ high though...
>
>wrt allocstall, I bet if I do a few runs, I'll see mucho variance there 
>(could be wrong.. hunch)

After 10 consecutive runs, stalls for 2.5.61cfq2 were 11060 vs. 3656 for 
2.5.61virgin.

(dang, hunch-o-meter needs calibration;)

         -Mike

Re: [PATCH] CFQ scheduler, #2

[Jens Axboe]

On Sat, Feb 15 2003, Rik van Riel wrote:
> On Sat, 15 Feb 2003, Mike Galbraith wrote:
> 
> >I gave this a burn, and under hefty load it seems to provide a bit of
> >anti-thrash benefit.
> 
> Judging from your log, it ends up stalling kswapd and
> dramatically increases the number of times that normal
> processes need to go into the pageout code.

With 30 odds processes, it doesn't take a whole lot for one process to
have its share of requests eaten.

> If this provides an anti-thrashing benefit, something's
> wrong with the VM in 2.5 ;)

It's not a vm problem. But it is a problem if kswapd + pdflush can
consume the entire request pool, stalling real user processes.

Mike, please retry the test with more requests available. CFQ does not
rely on request queue length for fairness. Just changes:

	 (queue_nr_requests > 128)
		queue_nr_requests = 128;

to

	 (queue_nr_requests > 512)
		queue_nr_requests = 512;

in ll_rw_blk.c:blk_dev_init() and see how that runs.

-- 
Jens Axboe

Re: [PATCH] CFQ scheduler, #2

[Mike Galbraith]

[-- Attachment #1: Type: text/plain, Size: 1302 bytes --]

At 05:35 PM 2/15/2003 +0100, Jens Axboe wrote:
>On Sat, Feb 15 2003, Rik van Riel wrote:
> > On Sat, 15 Feb 2003, Mike Galbraith wrote:
> >
> > >I gave this a burn, and under hefty load it seems to provide a bit of
> > >anti-thrash benefit.
> >
> > Judging from your log, it ends up stalling kswapd and
> > dramatically increases the number of times that normal
> > processes need to go into the pageout code.
>
>With 30 odds processes, it doesn't take a whole lot for one process to
>have its share of requests eaten.
>
> > If this provides an anti-thrashing benefit, something's
> > wrong with the VM in 2.5 ;)
>
>It's not a vm problem. But it is a problem if kswapd + pdflush can
>consume the entire request pool, stalling real user processes.
>
>Mike, please retry the test with more requests available. CFQ does not
>rely on request queue length for fairness. Just changes:
>
>         (queue_nr_requests > 128)
>                 queue_nr_requests = 128;
>
>to
>
>         (queue_nr_requests > 512)
>                 queue_nr_requests = 512;
>
>in ll_rw_blk.c:blk_dev_init() and see how that runs.

Results attached.  512 comes out to be 240 on this box (128MB).  I also did 
a burn with it hardwired to 512 on GP.  Throughput numbers cut since 
there's all within expected jitter.

         -Mike

[-- Attachment #2: xx.txt --]
[-- Type: text/plain, Size: 1849 bytes --]

/proc/vmstat 2.5.61cfq2   2.5.61virgin  cfq2-512(240)    cfq2-512
-----------------------------------------------------------------
nr_dirty             20             13             9           12
nr_writeback          0              0             0            0
nr_pagecache       7308           7593          7176         7737
nr_page_table_pages  85             85            85           85
nr_reverse_maps    3229           3198          3254         3159
nr_mapped           599            599           608          583
nr_slab            1203           1184          1169         1237
pgpgin          1767432        1911614       1758501      1775402
pgpgout         1606743        1746497       1595920      1654366
pswpin           311297         338436        307811       311515
pswpout          371161         406675        369132       383302
pgalloc         3037961        3070811       3030482      3020966
pgfree          3060825        3093420       3053524      3043355
pgactivate       142329         135616        134968       136655
pgdeactivate     514672         507026        481156       501111
pgfault         4896877        4928530       4891987      4913594
pgmajfault        74342          84476         74058        82857
pgscan          2751953        5328260       3250880      3797919
pgrefill        1821561        1972715       1896119      2057461
pgsteal          528014         575301        528513       529011
pginodesteal          0              0             0            0
kswapd_steal     380282         522126        405078       410382
kswapd_inodesteal  7010           7132          6704         6829
pageoutrun         1107           1956          1263         1259
allocstall         3472           1238          2865         2782
pgrotated        358243         413450        365914       387277