Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 8b3e6cdc authored by Dan Williams's avatar Dan Williams Committed by Linus Torvalds
Browse files

md: introduce get_priority_stripe() to improve raid456 write performance 



Improve write performance by preventing the delayed_list from dumping all its
stripes onto the handle_list in one shot.  Delayed stripes are now further
delayed by being held on the 'hold_list'.  The 'hold_list' is bypassed when:

  * a STRIPE_IO_STARTED stripe is found at the head of 'handle_list'
  * 'handle_list' is empty and i/o is being done to satisfy full stripe-width
    write requests
  * 'bypass_count' is less than 'bypass_threshold'.  By default the threshold
    is 1, i.e. every other stripe handled is a preread stripe provided the
    top two conditions are false.

Benchmark data:
System: 2x Xeon 5150, 4x SATA, mem=1GB
Baseline: 2.6.24-rc7
Configuration: mdadm --create /dev/md0 /dev/sd[b-e] -n 4 -l 5 --assume-clean
Test1: dd if=/dev/zero of=/dev/md0 bs=1024k count=2048
  * patched:  +33% (stripe_cache_size = 256), +25% (stripe_cache_size = 512)

Test2: tiobench --size 2048 --numruns 5 --block 4096 --block 131072 (XFS)
  * patched: +13%
  * patched + preread_bypass_threshold = 0: +37%

Changes since v1:
* reduce bypass_threshold from (chunk_size / sectors_per_chunk) to (1) and
  make it configurable.  This defaults to fairness and modest performance
  gains out of the box.
Changes since v2:
* [neilb@suse.de]: kill STRIPE_PRIO_HI and preread_needed as they are not
  necessary, the important change was clearing STRIPE_DELAYED in
  add_stripe_bio and this has been moved out to make_request for the hang
  fix.
* [neilb@suse.de]: simplify get_priority_stripe
* [dan.j.williams@intel.com]: reset the bypass_count when ->hold_list is
  sampled empty (+11%)
* [dan.j.williams@intel.com]: decrement the bypass_count at the detection
  of stripes being naturally promoted off of hold_list +2%.  Note, resetting
  bypass_count instead of decrementing on these events yields +4% but that is
  probably too aggressive.
Changes since v3:
* cosmetic fixups

Tested-by: default avatarJames W. Laferriere <babydr@baby-dragons.com>
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Signed-off-by: default avatarNeil Brown <neilb@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e46b272b

Documentation/md.txt

+6 −0
Original line number Diff line number Diff line
@@ -450,3 +450,9 @@ These currently include 
      there are upper and lower limits (32768, 16).  Default is 128.

  strip_cache_active (currently raid5 only)

      number of active entries in the stripe cache

  preread_bypass_threshold (currently raid5 only)

      number of times a stripe requiring preread will be bypassed by

      a stripe that does not require preread.  For fairness defaults

      to 1.  Setting this to 0 disables bypass accounting and

      requires preread stripes to wait until all full-width stripe-

      writes are complete.  Valid values are 0 to stripe_cache_size.

drivers/md/raid5.c

+112 −10
Original line number Diff line number Diff line
@@ -63,6 +63,7 @@ 
#define STRIPE_SHIFT		(PAGE_SHIFT - 9)

#define STRIPE_SECTORS		(STRIPE_SIZE>>9)

#define	IO_THRESHOLD		1

#define BYPASS_THRESHOLD	1

#define NR_HASH			(PAGE_SIZE / sizeof(struct hlist_head))

#define HASH_MASK		(NR_HASH - 1)
@@ -398,6 +399,7 @@ static void ops_run_io(struct stripe_head *sh) 


	might_sleep();



	set_bit(STRIPE_IO_STARTED, &sh->state);

	for (i = disks; i--; ) {

		int rw;

		struct bio *bi;
@@ -1720,6 +1722,9 @@ handle_write_operations5(struct stripe_head *sh, int rcw, int expand) 
				locked++;

			}

		}

		if (locked + 1 == disks)

			if (!test_and_set_bit(STRIPE_FULL_WRITE, &sh->state))

				atomic_inc(&sh->raid_conf->pending_full_writes);

	} else {

		BUG_ON(!(test_bit(R5_UPTODATE, &sh->dev[pd_idx].flags) ||

			test_bit(R5_Wantcompute, &sh->dev[pd_idx].flags)));
@@ -1947,6 +1952,9 @@ handle_requests_to_failed_array(raid5_conf_t *conf, struct stripe_head *sh, 
					STRIPE_SECTORS, 0, 0);

	}



	if (test_and_clear_bit(STRIPE_FULL_WRITE, &sh->state))

		if (atomic_dec_and_test(&conf->pending_full_writes))

			md_wakeup_thread(conf->mddev->thread);

}



/* __handle_issuing_new_read_requests5 - returns 0 if there are no more disks
@@ -2149,6 +2157,10 @@ static void handle_completed_write_requests(raid5_conf_t *conf, 
							0);

			}

		}



	if (test_and_clear_bit(STRIPE_FULL_WRITE, &sh->state))

		if (atomic_dec_and_test(&conf->pending_full_writes))

			md_wakeup_thread(conf->mddev->thread);

}



static void handle_issuing_new_write_requests5(raid5_conf_t *conf,
@@ -2333,6 +2345,9 @@ static void handle_issuing_new_write_requests6(raid5_conf_t *conf, 
				s->locked++;

				set_bit(R5_Wantwrite, &sh->dev[i].flags);

			}

		if (s->locked == disks)

			if (!test_and_set_bit(STRIPE_FULL_WRITE, &sh->state))

				atomic_inc(&conf->pending_full_writes);

		/* after a RECONSTRUCT_WRITE, the stripe MUST be in-sync */

		set_bit(STRIPE_INSYNC, &sh->state);
@@ -3094,6 +3109,8 @@ static void handle_stripe6(struct stripe_head *sh, struct page *tmp_page) 
		else

			continue;



		set_bit(STRIPE_IO_STARTED, &sh->state);



		bi = &sh->dev[i].req;



		bi->bi_rw = rw;
@@ -3164,7 +3181,7 @@ static void raid5_activate_delayed(raid5_conf_t *conf) 
			clear_bit(STRIPE_DELAYED, &sh->state);

			if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))

				atomic_inc(&conf->preread_active_stripes);

			list_add_tail(&sh->lru, &conf->handle_list);

			list_add_tail(&sh->lru, &conf->hold_list);

		}

	} else

		blk_plug_device(conf->mddev->queue);
@@ -3442,6 +3459,58 @@ static int chunk_aligned_read(struct request_queue *q, struct bio * raid_bio) 
	}

}



/* __get_priority_stripe - get the next stripe to process

 *

 * Full stripe writes are allowed to pass preread active stripes up until

 * the bypass_threshold is exceeded.  In general the bypass_count

 * increments when the handle_list is handled before the hold_list; however, it

 * will not be incremented when STRIPE_IO_STARTED is sampled set signifying a

 * stripe with in flight i/o.  The bypass_count will be reset when the

 * head of the hold_list has changed, i.e. the head was promoted to the

 * handle_list.

 */

static struct stripe_head *__get_priority_stripe(raid5_conf_t *conf)

{

	struct stripe_head *sh;



	pr_debug("%s: handle: %s hold: %s full_writes: %d bypass_count: %d\n",

		  __func__,

		  list_empty(&conf->handle_list) ? "empty" : "busy",

		  list_empty(&conf->hold_list) ? "empty" : "busy",

		  atomic_read(&conf->pending_full_writes), conf->bypass_count);



	if (!list_empty(&conf->handle_list)) {

		sh = list_entry(conf->handle_list.next, typeof(*sh), lru);



		if (list_empty(&conf->hold_list))

			conf->bypass_count = 0;

		else if (!test_bit(STRIPE_IO_STARTED, &sh->state)) {

			if (conf->hold_list.next == conf->last_hold)

				conf->bypass_count++;

			else {

				conf->last_hold = conf->hold_list.next;

				conf->bypass_count -= conf->bypass_threshold;

				if (conf->bypass_count < 0)

					conf->bypass_count = 0;

			}

		}

	} else if (!list_empty(&conf->hold_list) &&

		   ((conf->bypass_threshold &&

		     conf->bypass_count > conf->bypass_threshold) ||

		    atomic_read(&conf->pending_full_writes) == 0)) {

		sh = list_entry(conf->hold_list.next,

				typeof(*sh), lru);

		conf->bypass_count -= conf->bypass_threshold;

		if (conf->bypass_count < 0)

			conf->bypass_count = 0;

	} else

		return NULL;



	list_del_init(&sh->lru);

	atomic_inc(&sh->count);

	BUG_ON(atomic_read(&sh->count) != 1);

	return sh;

}



static int make_request(struct request_queue *q, struct bio * bi)

{
@@ -3914,7 +3983,6 @@ static void raid5d(mddev_t *mddev) 
	handled = 0;

	spin_lock_irq(&conf->device_lock);

	while (1) {

		struct list_head *first;

		struct bio *bio;



		if (conf->seq_flush != conf->seq_write) {
@@ -3936,17 +4004,12 @@ static void raid5d(mddev_t *mddev) 
			handled++;

		}



		if (list_empty(&conf->handle_list)) {

		sh = __get_priority_stripe(conf);



		if (!sh) {

			async_tx_issue_pending_all();

			break;

		}



		first = conf->handle_list.next;

		sh = list_entry(first, struct stripe_head, lru);



		list_del_init(first);

		atomic_inc(&sh->count);

		BUG_ON(atomic_read(&sh->count)!= 1);

		spin_unlock_irq(&conf->device_lock);

		

		handled++;
@@ -4010,6 +4073,42 @@ raid5_stripecache_size = __ATTR(stripe_cache_size, S_IRUGO | S_IWUSR, 
				raid5_show_stripe_cache_size,

				raid5_store_stripe_cache_size);



static ssize_t

raid5_show_preread_threshold(mddev_t *mddev, char *page)

{

	raid5_conf_t *conf = mddev_to_conf(mddev);

	if (conf)

		return sprintf(page, "%d\n", conf->bypass_threshold);

	else

		return 0;

}



static ssize_t

raid5_store_preread_threshold(mddev_t *mddev, const char *page, size_t len)

{

	raid5_conf_t *conf = mddev_to_conf(mddev);

	char *end;

	int new;

	if (len >= PAGE_SIZE)

		return -EINVAL;

	if (!conf)

		return -ENODEV;



	new = simple_strtoul(page, &end, 10);

	if (!*page || (*end && *end != '\n'))

		return -EINVAL;

	if (new > conf->max_nr_stripes || new < 0)

		return -EINVAL;

	conf->bypass_threshold = new;

	return len;

}



static struct md_sysfs_entry

raid5_preread_bypass_threshold = __ATTR(preread_bypass_threshold,

					S_IRUGO | S_IWUSR,

					raid5_show_preread_threshold,

					raid5_store_preread_threshold);



static ssize_t

stripe_cache_active_show(mddev_t *mddev, char *page)

{
@@ -4026,6 +4125,7 @@ raid5_stripecache_active = __ATTR_RO(stripe_cache_active); 
static struct attribute *raid5_attrs[] =  {

	&raid5_stripecache_size.attr,

	&raid5_stripecache_active.attr,

	&raid5_preread_bypass_threshold.attr,

	NULL,

};

static struct attribute_group raid5_attrs_group = {
@@ -4130,12 +4230,14 @@ static int run(mddev_t *mddev) 
	init_waitqueue_head(&conf->wait_for_stripe);

	init_waitqueue_head(&conf->wait_for_overlap);

	INIT_LIST_HEAD(&conf->handle_list);

	INIT_LIST_HEAD(&conf->hold_list);

	INIT_LIST_HEAD(&conf->delayed_list);

	INIT_LIST_HEAD(&conf->bitmap_list);

	INIT_LIST_HEAD(&conf->inactive_list);

	atomic_set(&conf->active_stripes, 0);

	atomic_set(&conf->preread_active_stripes, 0);

	atomic_set(&conf->active_aligned_reads, 0);

	conf->bypass_threshold = BYPASS_THRESHOLD;



	pr_debug("raid5: run(%s) called.\n", mdname(mddev));

include/linux/raid/raid5.h

+7 −0
Original line number Diff line number Diff line
@@ -252,6 +252,8 @@ struct r6_state { 
#define	STRIPE_EXPANDING	9

#define	STRIPE_EXPAND_SOURCE	10

#define	STRIPE_EXPAND_READY	11

#define	STRIPE_IO_STARTED	12 /* do not count towards 'bypass_count' */

#define	STRIPE_FULL_WRITE	13 /* all blocks are set to be overwritten */

/*

 * Operations flags (in issue order)

 */
@@ -316,12 +318,17 @@ struct raid5_private_data { 
	int			previous_raid_disks;



	struct list_head	handle_list; /* stripes needing handling */

	struct list_head	hold_list; /* preread ready stripes */

	struct list_head	delayed_list; /* stripes that have plugged requests */

	struct list_head	bitmap_list; /* stripes delaying awaiting bitmap update */

	struct bio		*retry_read_aligned; /* currently retrying aligned bios   */

	struct bio		*retry_read_aligned_list; /* aligned bios retry list  */

	atomic_t		preread_active_stripes; /* stripes with scheduled io */

	atomic_t		active_aligned_reads;

	atomic_t		pending_full_writes; /* full write backlog */

	int			bypass_count; /* bypassed prereads */

	int			bypass_threshold; /* preread nice */

	struct list_head	*last_hold; /* detect hold_list promotions */



	atomic_t		reshape_stripes; /* stripes with pending writes for reshape */

	/* unfortunately we need two cache names as we temporarily have