dm mpath: add service time load balancer
This patch adds a service time oriented dynamic load balancer, dm-service-time, which selects the path with the shortest estimated service time for the incoming I/O. The service time is estimated by dividing the in-flight I/O size by a performance value of each path. The performance value can be given as a table argument at the table loading time. If no performance value is given, all paths are considered equal. Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Kiyoshi Ueda
Alasdair G Kergon
parent
fd5e033908
commit
f392ba889b
4 changed files with 441 additions and 0 deletions
91
Documentation/device-mapper/dm-service-time.txt
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91
Documentation/device-mapper/dm-service-time.txt
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@ -0,0 +1,91 @@
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dm-service-time
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===============
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dm-service-time is a path selector module for device-mapper targets,
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which selects a path with the shortest estimated service time for
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the incoming I/O.
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The service time for each path is estimated by dividing the total size
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of in-flight I/Os on a path with the performance value of the path.
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The performance value is a relative throughput value among all paths
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in a path-group, and it can be specified as a table argument.
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The path selector name is 'service-time'.
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Table parameters for each path: [<repeat_count> [<relative_throughput>]]
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<repeat_count>: The number of I/Os to dispatch using the selected
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path before switching to the next path.
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If not given, internal default is used. To check
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the default value, see the activated table.
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<relative_throughput>: The relative throughput value of the path
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among all paths in the path-group.
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The valid range is 0-100.
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If not given, minimum value '1' is used.
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If '0' is given, the path isn't selected while
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other paths having a positive value are available.
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Status for each path: <status> <fail-count> <in-flight-size> \
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<relative_throughput>
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<status>: 'A' if the path is active, 'F' if the path is failed.
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<fail-count>: The number of path failures.
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<in-flight-size>: The size of in-flight I/Os on the path.
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<relative_throughput>: The relative throughput value of the path
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among all paths in the path-group.
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Algorithm
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=========
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dm-service-time adds the I/O size to 'in-flight-size' when the I/O is
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dispatched and substracts when completed.
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Basically, dm-service-time selects a path having minimum service time
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which is calculated by:
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('in-flight-size' + 'size-of-incoming-io') / 'relative_throughput'
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However, some optimizations below are used to reduce the calculation
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as much as possible.
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1. If the paths have the same 'relative_throughput', skip
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the division and just compare the 'in-flight-size'.
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2. If the paths have the same 'in-flight-size', skip the division
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and just compare the 'relative_throughput'.
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3. If some paths have non-zero 'relative_throughput' and others
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have zero 'relative_throughput', ignore those paths with zero
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'relative_throughput'.
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If such optimizations can't be applied, calculate service time, and
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compare service time.
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If calculated service time is equal, the path having maximum
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'relative_throughput' may be better. So compare 'relative_throughput'
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then.
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Examples
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========
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In case that 2 paths (sda and sdb) are used with repeat_count == 128
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and sda has an average throughput 1GB/s and sdb has 4GB/s,
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'relative_throughput' value may be '1' for sda and '4' for sdb.
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# echo "0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 1 8:16 128 4" \
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dmsetup create test
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#
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# dmsetup table
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test: 0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 1 8:16 128 4
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#
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# dmsetup status
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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
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Or '2' for sda and '8' for sdb would be also true.
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# echo "0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 2 8:16 128 8" \
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dmsetup create test
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#
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# dmsetup table
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test: 0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 2 8:16 128 8
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#
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# dmsetup status
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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
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@ -258,6 +258,16 @@ config DM_MULTIPATH_QL
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If unsure, say N.
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config DM_MULTIPATH_ST
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tristate "I/O Path Selector based on the service time"
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depends on DM_MULTIPATH
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---help---
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This path selector is a dynamic load balancer which selects
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the path expected to complete the incoming I/O in the shortest
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time.
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If unsure, say N.
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config DM_DELAY
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tristate "I/O delaying target (EXPERIMENTAL)"
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depends on BLK_DEV_DM && EXPERIMENTAL
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@ -37,6 +37,7 @@ obj-$(CONFIG_DM_CRYPT) += dm-crypt.o
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obj-$(CONFIG_DM_DELAY) += dm-delay.o
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obj-$(CONFIG_DM_MULTIPATH) += dm-multipath.o dm-round-robin.o
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obj-$(CONFIG_DM_MULTIPATH_QL) += dm-queue-length.o
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obj-$(CONFIG_DM_MULTIPATH_ST) += dm-service-time.o
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obj-$(CONFIG_DM_SNAPSHOT) += dm-snapshot.o
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obj-$(CONFIG_DM_MIRROR) += dm-mirror.o dm-log.o dm-region-hash.o
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obj-$(CONFIG_DM_ZERO) += dm-zero.o
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339
drivers/md/dm-service-time.c
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339
drivers/md/dm-service-time.c
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@ -0,0 +1,339 @@
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/*
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* Copyright (C) 2007-2009 NEC Corporation. All Rights Reserved.
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*
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* Module Author: Kiyoshi Ueda
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*
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* This file is released under the GPL.
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*
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* Throughput oriented path selector.
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*/
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#include "dm.h"
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#include "dm-path-selector.h"
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#define DM_MSG_PREFIX "multipath service-time"
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#define ST_MIN_IO 1
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#define ST_MAX_RELATIVE_THROUGHPUT 100
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#define ST_MAX_RELATIVE_THROUGHPUT_SHIFT 7
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#define ST_MAX_INFLIGHT_SIZE ((size_t)-1 >> ST_MAX_RELATIVE_THROUGHPUT_SHIFT)
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#define ST_VERSION "0.2.0"
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struct selector {
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struct list_head valid_paths;
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struct list_head failed_paths;
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};
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struct path_info {
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struct list_head list;
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struct dm_path *path;
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unsigned repeat_count;
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unsigned relative_throughput;
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atomic_t in_flight_size; /* Total size of in-flight I/Os */
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};
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static struct selector *alloc_selector(void)
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{
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struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
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if (s) {
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INIT_LIST_HEAD(&s->valid_paths);
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INIT_LIST_HEAD(&s->failed_paths);
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}
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return s;
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}
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static int st_create(struct path_selector *ps, unsigned argc, char **argv)
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{
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struct selector *s = alloc_selector();
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if (!s)
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return -ENOMEM;
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ps->context = s;
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return 0;
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}
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static void free_paths(struct list_head *paths)
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{
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struct path_info *pi, *next;
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list_for_each_entry_safe(pi, next, paths, list) {
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list_del(&pi->list);
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kfree(pi);
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}
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}
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static void st_destroy(struct path_selector *ps)
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{
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struct selector *s = ps->context;
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free_paths(&s->valid_paths);
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free_paths(&s->failed_paths);
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kfree(s);
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ps->context = NULL;
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}
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static int st_status(struct path_selector *ps, struct dm_path *path,
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status_type_t type, char *result, unsigned maxlen)
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{
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unsigned sz = 0;
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struct path_info *pi;
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if (!path)
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DMEMIT("0 ");
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else {
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pi = path->pscontext;
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switch (type) {
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case STATUSTYPE_INFO:
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DMEMIT("%d %u ", atomic_read(&pi->in_flight_size),
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pi->relative_throughput);
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break;
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case STATUSTYPE_TABLE:
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DMEMIT("%u %u ", pi->repeat_count,
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pi->relative_throughput);
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break;
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}
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}
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return sz;
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}
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static int st_add_path(struct path_selector *ps, struct dm_path *path,
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int argc, char **argv, char **error)
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{
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struct selector *s = ps->context;
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struct path_info *pi;
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unsigned repeat_count = ST_MIN_IO;
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unsigned relative_throughput = 1;
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/*
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* Arguments: [<repeat_count> [<relative_throughput>]]
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* <repeat_count>: The number of I/Os before switching path.
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* If not given, default (ST_MIN_IO) is used.
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* <relative_throughput>: The relative throughput value of
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* the path among all paths in the path-group.
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* The valid range: 0-<ST_MAX_RELATIVE_THROUGHPUT>
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* If not given, minimum value '1' is used.
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* If '0' is given, the path isn't selected while
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* other paths having a positive value are
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* available.
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*/
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if (argc > 2) {
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*error = "service-time ps: incorrect number of arguments";
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return -EINVAL;
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}
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if (argc && (sscanf(argv[0], "%u", &repeat_count) != 1)) {
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*error = "service-time ps: invalid repeat count";
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return -EINVAL;
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}
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if ((argc == 2) &&
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(sscanf(argv[1], "%u", &relative_throughput) != 1 ||
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relative_throughput > ST_MAX_RELATIVE_THROUGHPUT)) {
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*error = "service-time ps: invalid relative_throughput value";
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return -EINVAL;
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}
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/* allocate the path */
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pi = kmalloc(sizeof(*pi), GFP_KERNEL);
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if (!pi) {
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*error = "service-time ps: Error allocating path context";
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return -ENOMEM;
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}
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pi->path = path;
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pi->repeat_count = repeat_count;
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pi->relative_throughput = relative_throughput;
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atomic_set(&pi->in_flight_size, 0);
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path->pscontext = pi;
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list_add_tail(&pi->list, &s->valid_paths);
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return 0;
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}
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static void st_fail_path(struct path_selector *ps, struct dm_path *path)
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{
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struct selector *s = ps->context;
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struct path_info *pi = path->pscontext;
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list_move(&pi->list, &s->failed_paths);
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}
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static int st_reinstate_path(struct path_selector *ps, struct dm_path *path)
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{
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struct selector *s = ps->context;
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struct path_info *pi = path->pscontext;
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list_move_tail(&pi->list, &s->valid_paths);
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return 0;
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}
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/*
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* Compare the estimated service time of 2 paths, pi1 and pi2,
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* for the incoming I/O.
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*
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* Returns:
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* < 0 : pi1 is better
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* 0 : no difference between pi1 and pi2
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* > 0 : pi2 is better
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*
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* Description:
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* Basically, the service time is estimated by:
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* ('pi->in-flight-size' + 'incoming') / 'pi->relative_throughput'
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* To reduce the calculation, some optimizations are made.
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* (See comments inline)
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*/
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static int st_compare_load(struct path_info *pi1, struct path_info *pi2,
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size_t incoming)
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{
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size_t sz1, sz2, st1, st2;
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sz1 = atomic_read(&pi1->in_flight_size);
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sz2 = atomic_read(&pi2->in_flight_size);
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/*
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* Case 1: Both have same throughput value. Choose less loaded path.
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*/
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if (pi1->relative_throughput == pi2->relative_throughput)
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return sz1 - sz2;
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/*
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* Case 2a: Both have same load. Choose higher throughput path.
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* Case 2b: One path has no throughput value. Choose the other one.
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*/
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if (sz1 == sz2 ||
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!pi1->relative_throughput || !pi2->relative_throughput)
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return pi2->relative_throughput - pi1->relative_throughput;
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/*
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* Case 3: Calculate service time. Choose faster path.
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* Service time using pi1:
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* st1 = (sz1 + incoming) / pi1->relative_throughput
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* Service time using pi2:
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* st2 = (sz2 + incoming) / pi2->relative_throughput
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*
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* To avoid the division, transform the expression to use
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* multiplication.
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* Because ->relative_throughput > 0 here, if st1 < st2,
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* the expressions below are the same meaning:
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* (sz1 + incoming) / pi1->relative_throughput <
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* (sz2 + incoming) / pi2->relative_throughput
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* (sz1 + incoming) * pi2->relative_throughput <
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* (sz2 + incoming) * pi1->relative_throughput
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* So use the later one.
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*/
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sz1 += incoming;
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sz2 += incoming;
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if (unlikely(sz1 >= ST_MAX_INFLIGHT_SIZE ||
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sz2 >= ST_MAX_INFLIGHT_SIZE)) {
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/*
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* Size may be too big for multiplying pi->relative_throughput
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* and overflow.
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* To avoid the overflow and mis-selection, shift down both.
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*/
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sz1 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
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sz2 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
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}
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st1 = sz1 * pi2->relative_throughput;
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st2 = sz2 * pi1->relative_throughput;
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if (st1 != st2)
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return st1 - st2;
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/*
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* Case 4: Service time is equal. Choose higher throughput path.
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*/
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return pi2->relative_throughput - pi1->relative_throughput;
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}
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static struct dm_path *st_select_path(struct path_selector *ps,
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unsigned *repeat_count, size_t nr_bytes)
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{
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struct selector *s = ps->context;
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struct path_info *pi = NULL, *best = NULL;
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if (list_empty(&s->valid_paths))
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return NULL;
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/* Change preferred (first in list) path to evenly balance. */
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list_move_tail(s->valid_paths.next, &s->valid_paths);
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list_for_each_entry(pi, &s->valid_paths, list)
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if (!best || (st_compare_load(pi, best, nr_bytes) < 0))
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best = pi;
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if (!best)
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return NULL;
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*repeat_count = best->repeat_count;
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return best->path;
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}
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static int st_start_io(struct path_selector *ps, struct dm_path *path,
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size_t nr_bytes)
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{
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struct path_info *pi = path->pscontext;
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atomic_add(nr_bytes, &pi->in_flight_size);
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return 0;
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}
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static int st_end_io(struct path_selector *ps, struct dm_path *path,
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size_t nr_bytes)
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{
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struct path_info *pi = path->pscontext;
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atomic_sub(nr_bytes, &pi->in_flight_size);
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return 0;
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}
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static struct path_selector_type st_ps = {
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.name = "service-time",
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.module = THIS_MODULE,
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.table_args = 2,
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.info_args = 2,
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.create = st_create,
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.destroy = st_destroy,
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.status = st_status,
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.add_path = st_add_path,
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.fail_path = st_fail_path,
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.reinstate_path = st_reinstate_path,
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.select_path = st_select_path,
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.start_io = st_start_io,
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.end_io = st_end_io,
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};
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static int __init dm_st_init(void)
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{
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int r = dm_register_path_selector(&st_ps);
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if (r < 0)
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DMERR("register failed %d", r);
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DMINFO("version " ST_VERSION " loaded");
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return r;
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}
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static void __exit dm_st_exit(void)
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{
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int r = dm_unregister_path_selector(&st_ps);
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if (r < 0)
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DMERR("unregister failed %d", r);
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}
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module_init(dm_st_init);
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module_exit(dm_st_exit);
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MODULE_DESCRIPTION(DM_NAME " throughput oriented path selector");
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MODULE_AUTHOR("Kiyoshi Ueda <k-ueda@ct.jp.nec.com>");
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MODULE_LICENSE("GPL");
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