dm mpath: add service time load balancer (f392ba88) · Commits · 戴 / test

Documentation/device-mapper/dm-service-time.txt

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		dm-service-time
		===============

		dm-service-time is a path selector module for device-mapper targets,
		which selects a path with the shortest estimated service time for
		the incoming I/O.

		The service time for each path is estimated by dividing the total size
		of in-flight I/Os on a path with the performance value of the path.
		The performance value is a relative throughput value among all paths
		in a path-group, and it can be specified as a table argument.

		The path selector name is 'service-time'.

		Table parameters for each path: [<repeat_count> [<relative_throughput>]]
		<repeat_count>: The number of I/Os to dispatch using the selected
		path before switching to the next path.
		If not given, internal default is used. To check
		the default value, see the activated table.
		<relative_throughput>: The relative throughput value of the path
		among all paths in the path-group.
		The valid range is 0-100.
		If not given, minimum value '1' is used.
		If '0' is given, the path isn't selected while
		other paths having a positive value are available.

		Status for each path: <status> <fail-count> <in-flight-size> \
		<relative_throughput>
		<status>: 'A' if the path is active, 'F' if the path is failed.
		<fail-count>: The number of path failures.
		<in-flight-size>: The size of in-flight I/Os on the path.
		<relative_throughput>: The relative throughput value of the path
		among all paths in the path-group.


		Algorithm
		=========

		dm-service-time adds the I/O size to 'in-flight-size' when the I/O is
		dispatched and substracts when completed.
		Basically, dm-service-time selects a path having minimum service time
		which is calculated by:

		('in-flight-size' + 'size-of-incoming-io') / 'relative_throughput'

		However, some optimizations below are used to reduce the calculation
		as much as possible.

		1. If the paths have the same 'relative_throughput', skip
		the division and just compare the 'in-flight-size'.

		2. If the paths have the same 'in-flight-size', skip the division
		and just compare the 'relative_throughput'.

		3. If some paths have non-zero 'relative_throughput' and others
		have zero 'relative_throughput', ignore those paths with zero
		'relative_throughput'.

		If such optimizations can't be applied, calculate service time, and
		compare service time.
		If calculated service time is equal, the path having maximum
		'relative_throughput' may be better. So compare 'relative_throughput'
		then.


		Examples
		========
		In case that 2 paths (sda and sdb) are used with repeat_count == 128
		and sda has an average throughput 1GB/s and sdb has 4GB/s,
		'relative_throughput' value may be '1' for sda and '4' for sdb.

		# echo "0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 1 8:16 128 4" \
		dmsetup create test
		#
		# dmsetup table
		test: 0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 1 8:16 128 4
		#
		# dmsetup status
		test: 0 10 multipath 2 0 0 0 1 1 E 0 2 2 8:0 A 0 0 1 8:16 A 0 0 4


		Or '2' for sda and '8' for sdb would be also true.

		# echo "0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 2 8:16 128 8" \
		dmsetup create test
		#
		# dmsetup table
		test: 0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 2 8:16 128 8
		#
		# dmsetup status
		test: 0 10 multipath 2 0 0 0 1 1 E 0 2 2 8:0 A 0 0 2 8:16 A 0 0 8

drivers/md/Kconfig

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		@@ -258,6 +258,16 @@ config DM_MULTIPATH_QL

		If unsure, say N.

		config DM_MULTIPATH_ST
		tristate "I/O Path Selector based on the service time"
		depends on DM_MULTIPATH
		---help---
		This path selector is a dynamic load balancer which selects
		the path expected to complete the incoming I/O in the shortest
		time.

		If unsure, say N.

		config DM_DELAY
		tristate "I/O delaying target (EXPERIMENTAL)"
		depends on BLK_DEV_DM && EXPERIMENTAL

drivers/md/Makefile

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		@@ -37,6 +37,7 @@ obj-$(CONFIG_DM_CRYPT) += dm-crypt.o
		obj-$(CONFIG_DM_DELAY) += dm-delay.o
		obj-$(CONFIG_DM_MULTIPATH) += dm-multipath.o dm-round-robin.o
		obj-$(CONFIG_DM_MULTIPATH_QL) += dm-queue-length.o
		obj-$(CONFIG_DM_MULTIPATH_ST) += dm-service-time.o
		obj-$(CONFIG_DM_SNAPSHOT) += dm-snapshot.o
		obj-$(CONFIG_DM_MIRROR) += dm-mirror.o dm-log.o dm-region-hash.o
		obj-$(CONFIG_DM_ZERO) += dm-zero.o

drivers/md/dm-service-time.c

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		/*
		* Copyright (C) 2007-2009 NEC Corporation. All Rights Reserved.
		*
		* Module Author: Kiyoshi Ueda
		*
		* This file is released under the GPL.
		*
		* Throughput oriented path selector.
		*/

		#include "dm.h"
		#include "dm-path-selector.h"

		#define DM_MSG_PREFIX "multipath service-time"
		#define ST_MIN_IO 1
		#define ST_MAX_RELATIVE_THROUGHPUT 100
		#define ST_MAX_RELATIVE_THROUGHPUT_SHIFT 7
		#define ST_MAX_INFLIGHT_SIZE ((size_t)-1 >> ST_MAX_RELATIVE_THROUGHPUT_SHIFT)
		#define ST_VERSION "0.2.0"

		struct selector {
		struct list_head valid_paths;
		struct list_head failed_paths;
		};

		struct path_info {
		struct list_head list;
		struct dm_path *path;
		unsigned repeat_count;
		unsigned relative_throughput;
		atomic_t in_flight_size; /* Total size of in-flight I/Os */
		};

		static struct selector *alloc_selector(void)
		{
		struct selector s = kmalloc(sizeof(s), GFP_KERNEL);

		if (s) {
		INIT_LIST_HEAD(&s->valid_paths);
		INIT_LIST_HEAD(&s->failed_paths);
		}

		return s;
		}

		static int st_create(struct path_selector ps, unsigned argc, char *argv)
		{
		struct selector *s = alloc_selector();

		if (!s)
		return -ENOMEM;

		ps->context = s;
		return 0;
		}

		static void free_paths(struct list_head *paths)
		{
		struct path_info pi, next;

		list_for_each_entry_safe(pi, next, paths, list) {
		list_del(&pi->list);
		kfree(pi);
		}
		}

		static void st_destroy(struct path_selector *ps)
		{
		struct selector *s = ps->context;

		free_paths(&s->valid_paths);
		free_paths(&s->failed_paths);
		kfree(s);
		ps->context = NULL;
		}

		static int st_status(struct path_selector ps, struct dm_path path,
		status_type_t type, char *result, unsigned maxlen)
		{
		unsigned sz = 0;
		struct path_info *pi;

		if (!path)
		DMEMIT("0 ");
		else {
		pi = path->pscontext;

		switch (type) {
		case STATUSTYPE_INFO:
		DMEMIT("%d %u ", atomic_read(&pi->in_flight_size),
		pi->relative_throughput);
		break;
		case STATUSTYPE_TABLE:
		DMEMIT("%u %u ", pi->repeat_count,
		pi->relative_throughput);
		break;
		}
		}

		return sz;
		}

		static int st_add_path(struct path_selector ps, struct dm_path path,
		int argc, char argv, char error)
		{
		struct selector *s = ps->context;
		struct path_info *pi;
		unsigned repeat_count = ST_MIN_IO;
		unsigned relative_throughput = 1;

		/*
		* Arguments: [<repeat_count> [<relative_throughput>]]
		* <repeat_count>: The number of I/Os before switching path.
		* If not given, default (ST_MIN_IO) is used.
		* <relative_throughput>: The relative throughput value of
		* the path among all paths in the path-group.
		* The valid range: 0-<ST_MAX_RELATIVE_THROUGHPUT>
		* If not given, minimum value '1' is used.
		* If '0' is given, the path isn't selected while
		* other paths having a positive value are
		* available.
		*/
		if (argc > 2) {
		*error = "service-time ps: incorrect number of arguments";
		return -EINVAL;
		}

		if (argc && (sscanf(argv[0], "%u", &repeat_count) != 1)) {
		*error = "service-time ps: invalid repeat count";
		return -EINVAL;
		}

		if ((argc == 2) &&
		(sscanf(argv[1], "%u", &relative_throughput) != 1 \|\|
		relative_throughput > ST_MAX_RELATIVE_THROUGHPUT)) {
		*error = "service-time ps: invalid relative_throughput value";
		return -EINVAL;
		}

		/* allocate the path */
		pi = kmalloc(sizeof(*pi), GFP_KERNEL);
		if (!pi) {
		*error = "service-time ps: Error allocating path context";
		return -ENOMEM;
		}

		pi->path = path;
		pi->repeat_count = repeat_count;
		pi->relative_throughput = relative_throughput;
		atomic_set(&pi->in_flight_size, 0);

		path->pscontext = pi;

		list_add_tail(&pi->list, &s->valid_paths);

		return 0;
		}

		static void st_fail_path(struct path_selector ps, struct dm_path path)
		{
		struct selector *s = ps->context;
		struct path_info *pi = path->pscontext;

		list_move(&pi->list, &s->failed_paths);
		}

		static int st_reinstate_path(struct path_selector ps, struct dm_path path)
		{
		struct selector *s = ps->context;
		struct path_info *pi = path->pscontext;

		list_move_tail(&pi->list, &s->valid_paths);

		return 0;
		}

		/*
		* Compare the estimated service time of 2 paths, pi1 and pi2,
		* for the incoming I/O.
		*
		* Returns:
		* < 0 : pi1 is better
		* 0 : no difference between pi1 and pi2
		* > 0 : pi2 is better
		*
		* Description:
		* Basically, the service time is estimated by:
		* ('pi->in-flight-size' + 'incoming') / 'pi->relative_throughput'
		* To reduce the calculation, some optimizations are made.
		* (See comments inline)
		*/
		static int st_compare_load(struct path_info pi1, struct path_info pi2,
		size_t incoming)
		{
		size_t sz1, sz2, st1, st2;

		sz1 = atomic_read(&pi1->in_flight_size);
		sz2 = atomic_read(&pi2->in_flight_size);

		/*
		* Case 1: Both have same throughput value. Choose less loaded path.
		*/
		if (pi1->relative_throughput == pi2->relative_throughput)
		return sz1 - sz2;

		/*
		* Case 2a: Both have same load. Choose higher throughput path.
		* Case 2b: One path has no throughput value. Choose the other one.
		*/
		if (sz1 == sz2 \|\|
		!pi1->relative_throughput \|\| !pi2->relative_throughput)
		return pi2->relative_throughput - pi1->relative_throughput;

		/*
		* Case 3: Calculate service time. Choose faster path.
		* Service time using pi1:
		* st1 = (sz1 + incoming) / pi1->relative_throughput
		* Service time using pi2:
		* st2 = (sz2 + incoming) / pi2->relative_throughput
		*
		* To avoid the division, transform the expression to use
		* multiplication.
		* Because ->relative_throughput > 0 here, if st1 < st2,
		* the expressions below are the same meaning:
		* (sz1 + incoming) / pi1->relative_throughput <
		* (sz2 + incoming) / pi2->relative_throughput
		* (sz1 + incoming) * pi2->relative_throughput <
		* (sz2 + incoming) * pi1->relative_throughput
		* So use the later one.
		*/
		sz1 += incoming;
		sz2 += incoming;
		if (unlikely(sz1 >= ST_MAX_INFLIGHT_SIZE \|\|
		sz2 >= ST_MAX_INFLIGHT_SIZE)) {
		/*
		* Size may be too big for multiplying pi->relative_throughput
		* and overflow.
		* To avoid the overflow and mis-selection, shift down both.
		*/
		sz1 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
		sz2 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
		}
		st1 = sz1 * pi2->relative_throughput;
		st2 = sz2 * pi1->relative_throughput;
		if (st1 != st2)
		return st1 - st2;

		/*
		* Case 4: Service time is equal. Choose higher throughput path.
		*/
		return pi2->relative_throughput - pi1->relative_throughput;
		}

		static struct dm_path st_select_path(struct path_selector ps,
		unsigned *repeat_count, size_t nr_bytes)
		{
		struct selector *s = ps->context;
		struct path_info pi = NULL, best = NULL;

		if (list_empty(&s->valid_paths))
		return NULL;

		/* Change preferred (first in list) path to evenly balance. */
		list_move_tail(s->valid_paths.next, &s->valid_paths);

		list_for_each_entry(pi, &s->valid_paths, list)
		if (!best \|\| (st_compare_load(pi, best, nr_bytes) < 0))
		best = pi;

		if (!best)
		return NULL;

		*repeat_count = best->repeat_count;

		return best->path;
		}

		static int st_start_io(struct path_selector ps, struct dm_path path,
		size_t nr_bytes)
		{
		struct path_info *pi = path->pscontext;

		atomic_add(nr_bytes, &pi->in_flight_size);

		return 0;
		}

		static int st_end_io(struct path_selector ps, struct dm_path path,
		size_t nr_bytes)
		{
		struct path_info *pi = path->pscontext;

		atomic_sub(nr_bytes, &pi->in_flight_size);

		return 0;
		}

		static struct path_selector_type st_ps = {
		.name = "service-time",
		.module = THIS_MODULE,
		.table_args = 2,
		.info_args = 2,
		.create = st_create,
		.destroy = st_destroy,
		.status = st_status,
		.add_path = st_add_path,
		.fail_path = st_fail_path,
		.reinstate_path = st_reinstate_path,
		.select_path = st_select_path,
		.start_io = st_start_io,
		.end_io = st_end_io,
		};

		static int __init dm_st_init(void)
		{
		int r = dm_register_path_selector(&st_ps);

		if (r < 0)
		DMERR("register failed %d", r);

		DMINFO("version " ST_VERSION " loaded");

		return r;
		}

		static void __exit dm_st_exit(void)
		{
		int r = dm_unregister_path_selector(&st_ps);

		if (r < 0)
		DMERR("unregister failed %d", r);
		}

		module_init(dm_st_init);
		module_exit(dm_st_exit);

		MODULE_DESCRIPTION(DM_NAME " throughput oriented path selector");
		MODULE_AUTHOR("Kiyoshi Ueda <k-ueda@ct.jp.nec.com>");
		MODULE_LICENSE("GPL");

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