[Devel] [PATCH 2/2] dm-ioband: I/O bandwidth controller v1.12.0: range-bw
Ryo Tsuruta
ryov at valinux.co.jp
Tue Jun 16 03:28:14 PDT 2009
range-bw was implemented as another I/O scheduling policy of dm-ioband
to support predicable I/O bandwidth between minimum and maximum
bandwidth defined by administrator. Here, minimum I/O bandwidth should
be guaranteed for stable performance or reliability of specific
process groups and I/O bandwidth over maximum should be throttled to
protect the limited I/O resource from over-provisioning in unnecessary
usage or to reserve the I/O bandwidth for another use.
Signed-off-by: Dong-Jae Kang <baramsori72 at gmail.com>
---
Documentation/device-mapper/range-bw.txt | 99 ++++
drivers/md/dm-ioband-rangebw.c | 678 +++++++++++++++++++++++++++++++
2 files changed, 777 insertions(+)
Index: linux-2.6.30/drivers/md/dm-ioband-rangebw.c
===================================================================
--- /dev/null
+++ linux-2.6.30/drivers/md/dm-ioband-rangebw.c
@@ -0,0 +1,678 @@
+/*
+ * dm-ioband-rangebw.c
+ *
+ * This is a I/O control policy to support the Range Bandwidth in Disk I/O.
+ * And this policy is for dm-ioband controller by Ryo Tsuruta,
+ * Hirokazu Takahashi
+ *
+ * Copyright (C) 2008 - 2011
+ * Electronics and Telecommunications Research Institute(ETRI)
+ *
+ * This program is free software. you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License(GPL) as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * Contact Information:
+ * Dong-Jae, Kang <djkang at etri.re.kr>, Chei-Yol,Kim <gauri at etri.re.kr>,
+ * Sung-In,Jung <sijung at etri.re.kr>
+ */
+
+#include <linux/bio.h>
+#include <linux/workqueue.h>
+#include <linux/rbtree.h>
+#include "dm.h"
+#include "md.h"
+#include "dm-ioband.h"
+
+static void range_bw_timeover(unsigned long);
+static void range_bw_timer_register(struct timer_list *,
+ unsigned long, unsigned long);
+
+/*
+ * Functions for Range Bandwidth(range-bw) policy based on
+ * the time slice and token.
+ */
+#define DEFAULT_BUCKET 2
+#define DEFAULT_TOKENPOOL 2048
+
+#define TIME_SLICE_EXPIRED 1
+#define TIME_SLICE_NOT_EXPIRED 0
+
+#define MINBW_IO_MODE 0
+#define LEFTOVER_IO_MODE 1
+#define RANGE_IO_MODE 2
+#define DEFAULT_IO_MODE 3
+#define NO_IO_MODE 4
+
+#define MINBW_PRIO_BASE 10
+#define OVER_IO_RATE 4
+
+#define DEFAULT_RANGE_BW "0:0"
+#define DEFAULT_MIN_BW 0
+#define DEFAULT_MAX_BW 0
+#define POLICY_PARAM_DELIM "=:,"
+
+static const int time_slice_base = HZ / 10;
+static const int range_time_slice_base = HZ / 50;
+static void do_nothing(void) {}
+/*
+ * g_restart_bios function for range-bw policy
+ */
+static int range_bw_restart_bios(struct ioband_device *dp)
+{
+ return 1;
+}
+
+/*
+ * Allocate the time slice when IO mode is MINBW_IO_MODE,
+ * RANGE_IO_MODE or LEFTOVER_IO_MODE
+ */
+static int set_time_slice(struct ioband_group *gp)
+{
+ struct ioband_device *dp = gp->c_banddev;
+ int dp_io_mode, gp_io_mode;
+ unsigned long now = jiffies;
+
+ dp_io_mode = dp->g_io_mode;
+ gp_io_mode = gp->c_io_mode;
+
+ gp->c_time_slice_start = now;
+
+ if (dp_io_mode == LEFTOVER_IO_MODE) {
+ gp->c_time_slice_end = now + gp->c_time_slice;
+ return 0;
+ }
+
+ if (gp_io_mode == MINBW_IO_MODE)
+ gp->c_time_slice_end = now + gp->c_time_slice;
+ else if (gp_io_mode == RANGE_IO_MODE)
+ gp->c_time_slice_end = now + range_time_slice_base;
+ else if (gp_io_mode == DEFAULT_IO_MODE)
+ gp->c_time_slice_end = now + time_slice_base;
+ else if (gp_io_mode == NO_IO_MODE) {
+ gp->c_time_slice_end = 0;
+ gp->c_time_slice_expired = TIME_SLICE_EXPIRED;
+ return 0;
+ }
+
+ gp->c_time_slice_expired = TIME_SLICE_NOT_EXPIRED;
+
+ return 0;
+}
+
+/*
+ * Calculate the priority of given ioband_group
+ */
+static int range_bw_priority(struct ioband_group *gp)
+{
+ struct ioband_device *dp = gp->c_banddev;
+ int prio = 0;
+
+ if (dp->g_io_mode == LEFTOVER_IO_MODE) {
+ prio = random32() % MINBW_PRIO_BASE;
+ if (prio == 0)
+ prio = 1;
+ } else if (gp->c_io_mode == MINBW_IO_MODE) {
+ prio = (gp->c_min_bw_token - gp->c_consumed_min_bw_token) *
+ MINBW_PRIO_BASE;
+ } else if (gp->c_io_mode == DEFAULT_IO_MODE) {
+ prio = MINBW_PRIO_BASE;
+ } else if (gp->c_io_mode == RANGE_IO_MODE) {
+ prio = MINBW_PRIO_BASE / 2;
+ } else {
+ prio = 0;
+ }
+
+ return prio;
+}
+
+/*
+ * Check whether this group has right to issue an I/O in range-bw policy mode.
+ * Return 0 if it doesn't have right, otherwise return the non-zero value.
+ */
+static int has_right_to_issue(struct ioband_group *gp)
+{
+ struct ioband_device *dp = gp->c_banddev;
+ int prio;
+
+ if (gp->c_prio_blocked > 0 || gp->c_blocked - gp->c_prio_blocked > 0) {
+ prio = range_bw_priority(gp);
+ if (prio <= 0)
+ return 1;
+ return prio;
+ }
+
+ if (gp == dp->g_running_gp) {
+
+ if (gp->c_time_slice_expired == TIME_SLICE_EXPIRED) {
+
+ gp->c_time_slice_expired = TIME_SLICE_NOT_EXPIRED;
+ gp->c_time_slice_end = 0;
+
+ return 0;
+ }
+
+ if (gp->c_time_slice_end == 0)
+ set_time_slice(gp);
+
+ return range_bw_priority(gp);
+
+ }
+
+ dp->g_running_gp = gp;
+ set_time_slice(gp);
+
+ return range_bw_priority(gp);
+}
+
+/*
+ * Reset all variables related with range-bw token and time slice
+ */
+static int reset_range_bw_token(struct ioband_group *gp, unsigned long now)
+{
+ struct ioband_device *dp = gp->c_banddev;
+ struct ioband_group *p;
+
+ list_for_each_entry(p, &dp->g_groups, c_list) {
+ p->c_consumed_min_bw_token = 0;
+ p->c_is_over_max_bw = MAX_BW_UNDER;
+ if (p->c_io_mode != DEFAULT_IO_MODE)
+ p->c_io_mode = MINBW_IO_MODE;
+ }
+
+ dp->g_consumed_min_bw_token = 0;
+
+ dp->g_next_time_period = now + HZ;
+ dp->g_time_period_expired = TIME_SLICE_NOT_EXPIRED;
+ dp->g_io_mode = MINBW_IO_MODE;
+
+ list_for_each_entry(p, &dp->g_groups, c_list) {
+ if (waitqueue_active(&p->c_max_bw_over_waitq))
+ wake_up_all(&p->c_max_bw_over_waitq);
+ }
+ return 0;
+}
+
+/*
+ * Use tokens(Increase the number of consumed token) to issue an I/O
+ * for guranteeing the range-bw. and check the expiration of local and
+ * global time slice, and overflow of max bw
+ */
+static int range_bw_consume_token(struct ioband_group *gp, int count, int flag)
+{
+ struct ioband_device *dp = gp->c_banddev;
+ struct ioband_group *p;
+ unsigned long now = jiffies;
+ int io_mode;
+
+ dp->g_current = gp;
+
+ if (dp->g_next_time_period == 0) {
+ dp->g_next_time_period = now + HZ;
+ dp->g_time_period_expired = TIME_SLICE_NOT_EXPIRED;
+ }
+
+ if (time_after(now, dp->g_next_time_period)) {
+ reset_range_bw_token(gp, now);
+ } else {
+ gp->c_consumed_min_bw_token += count;
+ dp->g_consumed_min_bw_token += count;
+
+ if (gp->c_max_bw > 0 && gp->c_consumed_min_bw_token >=
+ gp->c_max_bw_token) {
+ gp->c_is_over_max_bw = MAX_BW_OVER;
+ gp->c_io_mode = NO_IO_MODE;
+ return R_YIELD;
+ }
+
+ if (gp->c_io_mode != RANGE_IO_MODE && gp->c_min_bw_token <=
+ gp->c_consumed_min_bw_token) {
+ gp->c_io_mode = RANGE_IO_MODE;
+
+ if (dp->g_total_min_bw_token <=
+ dp->g_consumed_min_bw_token) {
+ list_for_each_entry(p, &dp->g_groups, c_list) {
+ if (p->c_io_mode == RANGE_IO_MODE ||
+ p->c_io_mode == DEFAULT_IO_MODE) {
+ io_mode = 1;
+ } else {
+ io_mode = 0;
+ break;
+ }
+ }
+
+ if (io_mode && dp->g_io_mode == MINBW_IO_MODE)
+ dp->g_io_mode = LEFTOVER_IO_MODE;
+ }
+ }
+ }
+
+ if (gp->c_time_slice_end != 0 &&
+ time_after(now, gp->c_time_slice_end)) {
+ gp->c_time_slice_expired = TIME_SLICE_EXPIRED;
+ return R_YIELD;
+ }
+
+ return R_OK;
+}
+
+static int is_no_io_mode(struct ioband_group *gp)
+{
+ if (gp->c_io_mode == NO_IO_MODE)
+ return 1;
+
+ return 0;
+}
+
+/*
+ * Check if this group is able to receive a new bio.
+ * in range bw policy, we only check that ioband device should be blocked
+ */
+static int range_bw_queue_full(struct ioband_group *gp)
+{
+ struct ioband_device *dp = gp->c_banddev;
+ unsigned long now, time_step;
+
+ if (is_no_io_mode(gp)) {
+ now = jiffies;
+ if (time_after(dp->g_next_time_period, now)) {
+ time_step = dp->g_next_time_period - now;
+ range_bw_timer_register(gp->c_timer,
+ (time_step + TIME_COMPENSATOR),
+ (unsigned long)gp);
+ wait_event_lock_irq(gp->c_max_bw_over_waitq,
+ !is_no_io_mode(gp),
+ dp->g_lock, do_nothing());
+ }
+ }
+
+ return (gp->c_blocked >= gp->c_limit);
+}
+
+/*
+ * Convert the bw valuse to the number of bw token
+ * bw : Kbyte unit bandwidth
+ * token_base : the number of tokens used for one 1Kbyte-size IO
+ * -- Attention : Currently, We support the 512byte or 1Kbyte per 1 token
+ */
+static int convert_bw_to_token(int bw, int token_unit)
+{
+ int token;
+ int token_base;
+
+ token_base = (1 << token_unit) / 4;
+ token = bw * token_base;
+
+ return token;
+}
+
+
+/*
+ * Allocate the time slice for MINBW_IO_MODE to each group
+ */
+static void range_bw_time_slice_init(struct ioband_group *gp)
+{
+ struct ioband_device *dp = gp->c_banddev;
+ struct ioband_group *p;
+
+ list_for_each_entry(p, &dp->g_groups, c_list) {
+
+ if (dp->g_min_bw_total == 0)
+ p->c_time_slice = time_slice_base;
+ else
+ p->c_time_slice = time_slice_base +
+ ((time_slice_base *
+ ((p->c_min_bw + p->c_max_bw) / 2)) /
+ dp->g_min_bw_total);
+ }
+}
+
+/*
+ * Allocate the range_bw and range_bw_token to the given group
+ */
+static void set_range_bw(struct ioband_group *gp, int new_min, int new_max)
+{
+ struct ioband_device *dp = gp->c_banddev;
+ struct ioband_group *p;
+ int token_unit;
+
+ dp->g_min_bw_total += (new_min - gp->c_min_bw);
+ gp->c_min_bw = new_min;
+
+ dp->g_max_bw_total += (new_max - gp->c_max_bw);
+ gp->c_max_bw = new_max;
+
+ if (new_min)
+ gp->c_io_mode = MINBW_IO_MODE;
+ else
+ gp->c_io_mode = DEFAULT_IO_MODE;
+
+ range_bw_time_slice_init(gp);
+
+ token_unit = dp->g_token_unit;
+ gp->c_min_bw_token = convert_bw_to_token(new_min, token_unit);
+ dp->g_total_min_bw_token =
+ convert_bw_to_token(dp->g_min_bw_total, token_unit);
+
+ gp->c_max_bw_token = convert_bw_to_token(new_max, token_unit);
+
+ if (dp->g_min_bw_total == 0) {
+ list_for_each_entry(p, &dp->g_groups, c_list)
+ p->c_limit = 1;
+ } else {
+ list_for_each_entry(p, &dp->g_groups, c_list) {
+ p->c_limit = dp->g_io_limit * 2 * p->c_min_bw /
+ dp->g_min_bw_total / OVER_IO_RATE + 1;
+ }
+ }
+
+ return;
+}
+
+/*
+ * Allocate the min_bw and min_bw_token to the given group
+ */
+static void set_min_bw(struct ioband_group *gp, int new)
+{
+ struct ioband_device *dp = gp->c_banddev;
+ struct ioband_group *p;
+ int token_unit;
+
+ dp->g_min_bw_total += (new - gp->c_min_bw);
+ gp->c_min_bw = new;
+
+ if (new)
+ gp->c_io_mode = MINBW_IO_MODE;
+ else
+ gp->c_io_mode = DEFAULT_IO_MODE;
+
+ range_bw_time_slice_init(gp);
+
+ token_unit = dp->g_token_unit;
+ gp->c_min_bw_token = convert_bw_to_token(gp->c_min_bw, token_unit);
+ dp->g_total_min_bw_token =
+ convert_bw_to_token(dp->g_min_bw_total, token_unit);
+
+ if (dp->g_min_bw_total == 0) {
+ list_for_each_entry(p, &dp->g_groups, c_list)
+ p->c_limit = 1;
+ } else {
+ list_for_each_entry(p, &dp->g_groups, c_list) {
+ p->c_limit = dp->g_io_limit * 2 * p->c_min_bw /
+ dp->g_min_bw_total / OVER_IO_RATE + 1;
+ }
+ }
+
+ return;
+}
+
+/*
+ * Allocate the max_bw and max_bw_token to the pointed group
+ */
+static void set_max_bw(struct ioband_group *gp, int new)
+{
+ struct ioband_device *dp = gp->c_banddev;
+ int token_unit;
+
+ token_unit = dp->g_token_unit;
+
+ dp->g_max_bw_total += (new - gp->c_max_bw);
+ gp->c_max_bw = new;
+ gp->c_max_bw_token = convert_bw_to_token(new, token_unit);
+
+ range_bw_time_slice_init(gp);
+
+ return;
+
+}
+
+static void init_range_bw_token_bucket(struct ioband_device *dp, int val)
+{
+ dp->g_token_bucket = (dp->g_io_limit * 2 * DEFAULT_BUCKET) <<
+ dp->g_token_unit;
+ if (!val)
+ val = DEFAULT_TOKENPOOL << dp->g_token_unit;
+ if (val < dp->g_token_bucket)
+ val = dp->g_token_bucket;
+ dp->g_carryover = val/dp->g_token_bucket;
+ dp->g_token_left = 0;
+}
+
+static int policy_range_bw_param(struct ioband_group *gp,
+ char *cmd, char *value)
+{
+ long val = 0;
+ int r = 0;
+ int err = 0, err1, err2;
+ char *min, *max;
+ long min_val, max_val;
+
+ if (value) {
+ min = strsep(&value, POLICY_PARAM_DELIM);
+ max = strsep(&value, POLICY_PARAM_DELIM);
+ if (!min || !max)
+ err = 1;
+ else {
+ err1 = strict_strtol(min, 0, &min_val);
+ err2 = strict_strtol(max, 0, &max_val);
+ err = (err1 || err2);
+ }
+ } else {
+ min_val = DEFAULT_MIN_BW;
+ max_val = DEFAULT_MAX_BW;
+ }
+
+ if (!strcmp(cmd, "range-bw")) {
+ if (!err && 0 <= min_val &&
+ min_val <= (INT_MAX / 2) && 0 <= max_val &&
+ max_val <= (INT_MAX / 2) && min_val <= max_val)
+ set_range_bw(gp, min_val, max_val);
+ else
+ r = -EINVAL;
+ } else if (!strcmp(cmd, "min-bw")) {
+ if (!err && 0 <= val && val <= (INT_MAX / 2))
+ set_min_bw(gp, val);
+ else
+ r = -EINVAL;
+ } else if (!strcmp(cmd, "max-bw")) {
+ if ((!err && 0 <= val && val <= (INT_MAX / 2) &&
+ gp->c_min_bw <= val) || val == 0)
+ set_max_bw(gp, val);
+ else
+ r = -EINVAL;
+ } else {
+ r = -EINVAL;
+ }
+ return r;
+}
+
+static int policy_range_bw_ctr(struct ioband_group *gp, char *arg)
+{
+ int ret;
+
+ init_waitqueue_head(&gp->c_max_bw_over_waitq);
+ spin_lock_init(&gp->c_lock);
+
+ gp->c_min_bw = 0;
+ gp->c_max_bw = 0;
+ gp->c_io_mode = DEFAULT_IO_MODE;
+ gp->c_time_slice_expired = TIME_SLICE_NOT_EXPIRED;
+ gp->c_min_bw_token = 0;
+ gp->c_max_bw_token = 0;
+ gp->c_consumed_min_bw_token = 0;
+ gp->c_is_over_max_bw = MAX_BW_UNDER;
+ gp->c_time_slice_start = 0;
+ gp->c_time_slice_end = 0;
+ gp->c_wait_p_count = 0;
+
+ gp->c_time_slice = time_slice_base;
+
+ gp->c_timer = kmalloc(sizeof(struct timer_list), GFP_KERNEL);
+ if (gp->c_timer == NULL)
+ return -EINVAL;
+ memset(gp->c_timer, 0, sizeof(struct timer_list));
+ gp->timer_set = 0;
+
+ ret = policy_range_bw_param(gp, "range-bw", arg);
+
+ return ret;
+}
+
+static void policy_range_bw_dtr(struct ioband_group *gp)
+{
+ struct ioband_device *dp = gp->c_banddev;
+
+ gp->c_time_slice = 0;
+ set_range_bw(gp, 0, 0);
+
+ dp->g_running_gp = NULL;
+
+ if (gp->c_timer != NULL) {
+ del_timer(gp->c_timer);
+ kfree(gp->c_timer);
+ }
+}
+
+static void policy_range_bw_show(struct ioband_group *gp, int *szp,
+ char *result, unsigned int maxlen)
+{
+ struct ioband_group *p;
+ struct ioband_device *dp = gp->c_banddev;
+ struct rb_node *node;
+ int sz = *szp; /* used in DMEMIT() */
+
+ DMEMIT(" %d :%d:%d", dp->g_token_bucket * dp->g_carryover,
+ gp->c_min_bw, gp->c_max_bw);
+
+ for (node = rb_first(&gp->c_group_root); node; node = rb_next(node)) {
+ p = rb_entry(node, struct ioband_group, c_group_node);
+ DMEMIT(" %d:%d:%d", p->c_id, p->c_min_bw, p->c_max_bw);
+ }
+ *szp = sz;
+}
+
+static int range_bw_prepare_token(struct ioband_group *gp,
+ struct bio *bio, int flag)
+{
+ struct ioband_device *dp = gp->c_banddev;
+ int unit;
+ int bio_count;
+ int token_count = 0;
+
+ unit = (1 << dp->g_token_unit);
+ bio_count = bio_sectors(bio);
+
+ if (unit == 8)
+ token_count = bio_count;
+ else if (unit == 4)
+ token_count = bio_count / 2;
+ else if (unit == 2)
+ token_count = bio_count / 4;
+ else if (unit == 1)
+ token_count = bio_count / 8;
+
+ return range_bw_consume_token(gp, token_count, flag);
+}
+
+void range_bw_timer_register(struct timer_list *ptimer,
+ unsigned long timeover, unsigned long gp)
+{
+ struct ioband_group *group = (struct ioband_group *)gp;
+
+ if (group->timer_set == 0) {
+ init_timer(ptimer);
+ ptimer->expires = get_jiffies_64() + timeover;
+ ptimer->data = gp;
+ ptimer->function = range_bw_timeover;
+ add_timer(ptimer);
+ group->timer_set = 1;
+ }
+}
+
+/*
+ * Timer Handler function to protect the all processes's hanging in
+ * lower min-bw configuration
+ */
+void range_bw_timeover(unsigned long gp)
+{
+ struct ioband_group *group = (struct ioband_group *)gp;
+
+ if (group->c_is_over_max_bw == MAX_BW_OVER)
+ group->c_is_over_max_bw = MAX_BW_UNDER;
+
+ if (group->c_io_mode == NO_IO_MODE)
+ group->c_io_mode = MINBW_IO_MODE;
+
+ if (waitqueue_active(&group->c_max_bw_over_waitq))
+ wake_up_all(&group->c_max_bw_over_waitq);
+
+ group->timer_set = 0;
+}
+
+/*
+ * <Method> <description>
+ * g_can_submit : To determine whether a given group has the right to
+ * submit BIOs. The larger the return value the higher the
+ * priority to submit. Zero means it has no right.
+ * g_prepare_bio : Called right before submitting each BIO.
+ * g_restart_bios : Called if this ioband device has some BIOs blocked but none
+ * of them can be submitted now. This method has to
+ * reinitialize the data to restart to submit BIOs and return
+ * 0 or 1.
+ * The return value 0 means that it has become able to submit
+ * them now so that this ioband device will continue its work.
+ * The return value 1 means that it is still unable to submit
+ * them so that this device will stop its work. And this
+ * policy module has to reactivate the device when it gets
+ * to be able to submit BIOs.
+ * g_hold_bio : To hold a given BIO until it is submitted.
+ * The default function is used when this method is undefined.
+ * g_pop_bio : To select and get the best BIO to submit.
+ * g_group_ctr : To initalize the policy own members of struct ioband_group.
+ * g_group_dtr : Called when struct ioband_group is removed.
+ * g_set_param : To update the policy own date.
+ * The parameters can be passed through "dmsetup message"
+ * command.
+ * g_should_block : Called every time this ioband device receive a BIO.
+ * Return 1 if a given group can't receive any more BIOs,
+ * otherwise return 0.
+ * g_show : Show the configuration.
+ */
+
+int policy_range_bw_init(struct ioband_device *dp, int argc, char **argv)
+{
+ long val;
+ int r = 0;
+
+ if (argc < 1)
+ val = 0;
+ else {
+ r = strict_strtol(argv[0], 0, &val);
+ if (r || val < 0)
+ return -EINVAL;
+ }
+
+ dp->g_can_submit = has_right_to_issue;
+ dp->g_prepare_bio = range_bw_prepare_token;
+ dp->g_restart_bios = range_bw_restart_bios;
+ dp->g_group_ctr = policy_range_bw_ctr;
+ dp->g_group_dtr = policy_range_bw_dtr;
+ dp->g_set_param = policy_range_bw_param;
+ dp->g_should_block = range_bw_queue_full;
+ dp->g_show = policy_range_bw_show;
+
+ dp->g_min_bw_total = 0;
+ dp->g_running_gp = NULL;
+ dp->g_total_min_bw_token = 0;
+ dp->g_io_mode = MINBW_IO_MODE;
+ dp->g_consumed_min_bw_token = 0;
+ dp->g_current = NULL;
+ dp->g_next_time_period = 0;
+ dp->g_time_period_expired = TIME_SLICE_NOT_EXPIRED;
+
+ dp->g_token_unit = PAGE_SHIFT - 9;
+ init_range_bw_token_bucket(dp, val);
+
+ return 0;
+}
Index: linux-2.6.30/Documentation/device-mapper/range-bw.txt
===================================================================
--- /dev/null
+++ linux-2.6.30/Documentation/device-mapper/range-bw.txt
@@ -0,0 +1,99 @@
+Range-BW I/O controller by Dong-Jae Kang <djkang at etri.re.kr>
+
+
+1. Introduction
+===============
+
+The design of Range-BW is related with three another parts, Cgroup,
+bio-cgroup (or blkio-cgroup) and dm-ioband and it was implemented as
+an additional controller for dm-ioband.
+Cgroup framework is used to support process grouping mechanism and
+bio-cgroup is used to control delayed I/O or non-direct I/O. Finally,
+dm-ioband is a kind of I/O controller allowing the proportional I/O
+bandwidth to process groups based on its priority.
+The supposed controller supports the process group-based range
+bandwidth according to the priority or importance of the group. Range
+bandwidth means the predicable I/O bandwidth with minimum and maximum
+value defined by administrator.
+
+Minimum I/O bandwidth should be guaranteed for stable performance or
+reliability of specific service and I/O bandwidth over maximum should
+be throttled to protect the limited I/O resource from
+over-provisioning in unnecessary usage or to reserve the I/O bandwidth
+for another use.
+So, Range-BW was implemented to include the two concepts, guaranteeing
+of minimum I/O requirement and limitation of unnecessary bandwidth
+depending on its priority.
+And it was implemented as device mapper driver such like dm-ioband.
+So, it is independent of the underlying specific I/O scheduler, for
+example, CFQ, AS, NOOP, deadline and so on.
+
+* Attention
+Range-BW supports the predicable I/O bandwidth, but it should be
+configured in the scope of total I/O bandwidth of the I/O system to
+guarantee the minimum I/O requirement. For example, if total I/O
+bandwidth is 40Mbytes/sec,
+
+the summary of I/O bandwidth configured in each process group should
+be equal or smaller than 40Mbytes/sec.
+So, we need to check total I/O bandwidth before set it up.
+
+2. Setup and Installation
+=========================
+
+This part is same with dm-ioband,
+../../Documentation/device-mapper/ioband.txt or
+http://sourceforge.net/apps/trac/ioband/wiki/dm-ioband/man/setup
+except the allocation of range-bw values.
+
+3. Usage
+========
+
+It is very useful to refer the documentation for dm-ioband in
+../../Documentation/device-mapper/ioband.txt or
+
+http://sourceforge.net/apps/trac/ioband/wiki/dm-ioband, because
+Range-BW follows the basic semantics of dm-ioband.
+This example is for range-bw configuration.
+
+# mount the cgroup
+mount -t cgroup -o blkio none /root/cgroup/blkio
+
+# create the process groups (3 groups)
+mkdir /root/cgroup/blkio/bgroup1
+mkdir /root/cgroup/blkio/bgroup2
+mkdir /root/cgroup/blkio/bgroup3
+
+# create the ioband device ( name : ioband1 )
+echo "0 $(blockdev --getsize /dev/sdb2) ioband /dev/sdb2 1 0 0 none
+range-bw 0 :0:0" | dmsetup create ioband1
+: Attention - device name (/dev/sdb2) should be modified depending on
+your system
+
+# init ioband device ( type and policy )
+dmsetup message ioband1 0 type cgroup
+dmsetup message ioband1 0 policy range-bw
+
+# attach the groups to the ioband device
+dmsetup message ioband1 0 attach 2
+dmsetup message ioband1 0 attach 3
+dmsetup message ioband1 0 attach 4
+: group number can be referred in /root/cgroup/blkio/bgroup1/blkio.id
+
+# allocate the values ( range-bw ) : XXX Kbytes
+: the sum of minimum I/O bandwidth in each group should be equal or
+smaller than total bandwidth to be supported by your system
+
+# range : about 100~500 Kbytes
+dmsetup message ioband1 0 range-bw 2:100:500
+
+# range : about 700~1000 Kbytes
+dmsetup message ioband1 0 range-bw 3:700:1000
+
+# range : about 30~35Mbytes
+dmsetup message ioband1 0 range-bw 4:30000:35000
+
+You can confirm the configuration of range-bw by using this command :
+[root at localhost range-bw]# dmsetup table --target ioband
+ioband1: 0 305235000 ioband 8:18 1 4 128 cgroup \
+ range-bw 16384 :0:0 2:100:500 3:700:1000 4:30000:35000
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