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Subject[PATCH 3/4] block: Core throttling logic implementation
Date
o Actual implementation of throttling policy.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
block/Kconfig | 12 +
block/Makefile | 1 +
block/blk-core.c | 24 ++
block/blk-throttle.c | 946 +++++++++++++++++++++++++++++++++++++++++++++
block/blk.h | 4 +-
block/cfq-iosched.c | 4 +
include/linux/blk_types.h | 3 +
include/linux/blkdev.h | 24 ++
init/Kconfig | 9 +-
9 files changed, 1023 insertions(+), 4 deletions(-)
create mode 100644 block/blk-throttle.c

diff --git a/block/Kconfig b/block/Kconfig
index 9be0b56..6c9213e 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -77,6 +77,18 @@ config BLK_DEV_INTEGRITY
T10/SCSI Data Integrity Field or the T13/ATA External Path
Protection. If in doubt, say N.

+config BLK_DEV_THROTTLING
+ bool "Block layer bio throttling support"
+ depends on BLK_CGROUP=y && EXPERIMENTAL
+ default n
+ ---help---
+ Block layer bio throttling support. It can be used to limit
+ the IO rate to a device. IO rate policies are per cgroup and
+ one needs to mount and use blkio cgroup controller for creating
+ cgroups and specifying per device IO rate policies.
+
+ See Documentation/cgroups/blkio-controller.txt for more information.
+
endif # BLOCK

config BLOCK_COMPAT
diff --git a/block/Makefile b/block/Makefile
index 0bb499a..c850d5e 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -9,6 +9,7 @@ obj-$(CONFIG_BLOCK) := elevator.o blk-core.o blk-tag.o blk-sysfs.o \

obj-$(CONFIG_BLK_DEV_BSG) += bsg.o
obj-$(CONFIG_BLK_CGROUP) += blk-cgroup.o
+obj-$(CONFIG_BLK_DEV_THROTTLING) += blk-throttle.o
obj-$(CONFIG_IOSCHED_NOOP) += noop-iosched.o
obj-$(CONFIG_IOSCHED_DEADLINE) += deadline-iosched.o
obj-$(CONFIG_IOSCHED_CFQ) += cfq-iosched.o
diff --git a/block/blk-core.c b/block/blk-core.c
index ee1a1e7..c4831b6 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -382,6 +382,7 @@ void blk_sync_queue(struct request_queue *q)
del_timer_sync(&q->unplug_timer);
del_timer_sync(&q->timeout);
cancel_work_sync(&q->unplug_work);
+ throtl_shutdown_timer_wq(q);
}
EXPORT_SYMBOL(blk_sync_queue);

@@ -459,6 +460,8 @@ void blk_cleanup_queue(struct request_queue *q)
if (q->elevator)
elevator_exit(q->elevator);

+ blk_throtl_exit(q);
+
blk_put_queue(q);
}
EXPORT_SYMBOL(blk_cleanup_queue);
@@ -515,6 +518,11 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
return NULL;
}

+ if (blk_throtl_init(q)) {
+ kmem_cache_free(blk_requestq_cachep, q);
+ return NULL;
+ }
+
setup_timer(&q->backing_dev_info.laptop_mode_wb_timer,
laptop_mode_timer_fn, (unsigned long) q);
init_timer(&q->unplug_timer);
@@ -1522,6 +1530,15 @@ static inline void __generic_make_request(struct bio *bio)
goto end_io;
}

+ blk_throtl_bio(q, &bio);
+
+ /*
+ * If bio = NULL, bio has been throttled and will be submitted
+ * later.
+ */
+ if (!bio)
+ break;
+
trace_block_bio_queue(q, bio);

ret = q->make_request_fn(q, bio);
@@ -2579,6 +2596,13 @@ int kblockd_schedule_work(struct request_queue *q, struct work_struct *work)
}
EXPORT_SYMBOL(kblockd_schedule_work);

+int kblockd_schedule_delayed_work(struct request_queue *q,
+ struct delayed_work *dwork, unsigned long delay)
+{
+ return queue_delayed_work(kblockd_workqueue, dwork, delay);
+}
+EXPORT_SYMBOL(kblockd_schedule_delayed_work);
+
int __init blk_dev_init(void)
{
BUILD_BUG_ON(__REQ_NR_BITS > 8 *
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
new file mode 100644
index 0000000..77ea2cf
--- /dev/null
+++ b/block/blk-throttle.c
@@ -0,0 +1,946 @@
+/*
+ * Interface for controlling IO bandwidth on a request queue
+ *
+ * Copyright (C) 2010 Vivek Goyal <vgoyal@redhat.com>
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+#include <linux/blktrace_api.h>
+#include "blk-cgroup.h"
+
+/* Max dispatch from a group in 1 round */
+static int throtl_grp_quantum = 8;
+
+/* Total max dispatch from all groups in one round */
+static int throtl_quantum = 32;
+
+/* Throttling is performed over 100ms slice and after that slice is renewed */
+static unsigned long throtl_slice = HZ/10; /* 100 ms */
+
+struct throtl_rb_root {
+ struct rb_root rb;
+ struct rb_node *left;
+ unsigned int count;
+ unsigned long min_disptime;
+};
+
+#define THROTL_RB_ROOT (struct throtl_rb_root) { .rb = RB_ROOT, .left = NULL, \
+ .count = 0, .min_disptime = 0}
+
+#define rb_entry_tg(node) rb_entry((node), struct throtl_grp, rb_node)
+
+struct throtl_grp {
+ /* List of throtl groups on the request queue*/
+ struct hlist_node tg_node;
+
+ /* active throtl group service_tree member */
+ struct rb_node rb_node;
+
+ /*
+ * Dispatch time in jiffies. This is the estimated time when group
+ * will unthrottle and is ready to dispatch more bio. It is used as
+ * key to sort active groups in service tree.
+ */
+ unsigned long disptime;
+
+ struct blkio_group blkg;
+ atomic_t ref;
+ unsigned int flags;
+
+ /* Two lists for READ and WRITE */
+ struct bio_list bio_lists[2];
+
+ /* Number of queued bios on READ and WRITE lists */
+ unsigned int nr_queued[2];
+
+ /* bytes per second rate limits */
+ uint64_t bps[2];
+
+ /* Number of bytes disptached in current slice */
+ uint64_t bytes_disp[2];
+
+ /* When did we start a new slice */
+ unsigned long slice_start[2];
+ unsigned long slice_end[2];
+};
+
+struct throtl_data
+{
+ /* List of throtl groups */
+ struct hlist_head tg_list;
+
+ /* service tree for active throtl groups */
+ struct throtl_rb_root tg_service_tree;
+
+ struct throtl_grp root_tg;
+ struct request_queue *queue;
+
+ /* Total Number of queued bios on READ and WRITE lists */
+ unsigned int nr_queued[2];
+
+ /* How many bios are on disp_list */
+ int nr_disp_list;
+
+ /*
+ * number of total undestroyed groups (excluding root group)
+ */
+ unsigned int nr_undestroyed_grps;
+
+ /* Bios queued for dispatch */
+ struct bio_list disp_list;
+
+ /* Work for dispatching throttled bios */
+ struct delayed_work throtl_work;
+};
+
+enum tg_state_flags {
+ THROTL_TG_FLAG_on_rr = 0, /* on round-robin busy list */
+};
+
+#define THROTL_TG_FNS(name) \
+static inline void throtl_mark_tg_##name(struct throtl_grp *tg) \
+{ \
+ (tg)->flags |= (1 << THROTL_TG_FLAG_##name); \
+} \
+static inline void throtl_clear_tg_##name(struct throtl_grp *tg) \
+{ \
+ (tg)->flags &= ~(1 << THROTL_TG_FLAG_##name); \
+} \
+static inline int throtl_tg_##name(const struct throtl_grp *tg) \
+{ \
+ return ((tg)->flags & (1 << THROTL_TG_FLAG_##name)) != 0; \
+}
+
+THROTL_TG_FNS(on_rr);
+
+#define throtl_log_tg(td, tg, fmt, args...) \
+ blk_add_trace_msg((td)->queue, "%s throtl " fmt, \
+ blkg_path(&(tg)->blkg), ##args); \
+
+#define throtl_log(td, fmt, args...) \
+ blk_add_trace_msg((td)->queue, "throtl " fmt, ##args)
+
+static inline struct throtl_grp *tg_of_blkg(struct blkio_group *blkg)
+{
+ if (blkg)
+ return container_of(blkg, struct throtl_grp, blkg);
+
+ return NULL;
+}
+
+static inline int total_nr_queued(struct throtl_data *td)
+{
+ return (td->nr_disp_list + td->nr_queued[0] + td->nr_queued[1]);
+}
+
+static inline struct throtl_grp *throtl_ref_get_tg(struct throtl_grp *tg)
+{
+ atomic_inc(&tg->ref);
+ return tg;
+}
+
+static void throtl_put_tg(struct throtl_grp *tg)
+{
+ BUG_ON(atomic_read(&tg->ref) <= 0);
+ if (!atomic_dec_and_test(&tg->ref))
+ return;
+ kfree(tg);
+}
+
+static struct throtl_grp * throtl_find_alloc_tg(struct throtl_data *td,
+ struct cgroup *cgroup)
+{
+ struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
+ struct throtl_grp *tg = NULL;
+ void *key = td;
+ struct backing_dev_info *bdi = &td->queue->backing_dev_info;
+ unsigned int major, minor;
+
+ /*
+ * TODO: Speed up blkiocg_lookup_group() by maintaining a radix
+ * tree of blkg (instead of traversing through hash list all
+ * the time.
+ */
+ tg = tg_of_blkg(blkiocg_lookup_group(blkcg, key));
+
+ /* Fill in device details for root group */
+ if (tg && !tg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
+ sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
+ tg->blkg.dev = MKDEV(major, minor);
+ goto done;
+ }
+
+ if (tg)
+ goto done;
+
+ tg = kzalloc_node(sizeof(*tg), GFP_ATOMIC, td->queue->node);
+ if (!tg)
+ goto done;
+
+ INIT_HLIST_NODE(&tg->tg_node);
+ RB_CLEAR_NODE(&tg->rb_node);
+ bio_list_init(&tg->bio_lists[0]);
+ bio_list_init(&tg->bio_lists[1]);
+
+ /*
+ * Take the initial reference that will be released on destroy
+ * This can be thought of a joint reference by cgroup and
+ * request queue which will be dropped by either request queue
+ * exit or cgroup deletion path depending on who is exiting first.
+ */
+ atomic_set(&tg->ref, 1);
+
+ /* Add group onto cgroup list */
+ sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
+ blkiocg_add_blkio_group(blkcg, &tg->blkg, (void *)td,
+ MKDEV(major, minor), BLKIO_POLICY_THROTL);
+
+ tg->bps[READ] = blkcg_get_read_bps(blkcg, tg->blkg.dev);
+ tg->bps[WRITE] = blkcg_get_write_bps(blkcg, tg->blkg.dev);
+
+ hlist_add_head(&tg->tg_node, &td->tg_list);
+ td->nr_undestroyed_grps++;
+done:
+ return tg;
+}
+
+static struct throtl_grp * throtl_get_tg(struct throtl_data *td)
+{
+ struct cgroup *cgroup;
+ struct throtl_grp *tg = NULL;
+
+ rcu_read_lock();
+ cgroup = task_cgroup(current, blkio_subsys_id);
+ tg = throtl_find_alloc_tg(td, cgroup);
+ if (!tg)
+ tg = &td->root_tg;
+ rcu_read_unlock();
+ return tg;
+}
+
+static struct throtl_grp *throtl_rb_first(struct throtl_rb_root *root)
+{
+ /* Service tree is empty */
+ if (!root->count)
+ return NULL;
+
+ if (!root->left)
+ root->left = rb_first(&root->rb);
+
+ if (root->left)
+ return rb_entry_tg(root->left);
+
+ return NULL;
+}
+
+static void rb_erase_init(struct rb_node *n, struct rb_root *root)
+{
+ rb_erase(n, root);
+ RB_CLEAR_NODE(n);
+}
+
+static void throtl_rb_erase(struct rb_node *n, struct throtl_rb_root *root)
+{
+ if (root->left == n)
+ root->left = NULL;
+ rb_erase_init(n, &root->rb);
+ --root->count;
+}
+
+static void update_min_dispatch_time(struct throtl_rb_root *st)
+{
+ struct throtl_grp *tg;
+
+ tg = throtl_rb_first(st);
+ if (!tg)
+ return;
+
+ st->min_disptime = tg->disptime;
+}
+
+static void
+tg_service_tree_add(struct throtl_rb_root *st, struct throtl_grp *tg)
+{
+ struct rb_node **node = &st->rb.rb_node;
+ struct rb_node *parent = NULL;
+ struct throtl_grp *__tg;
+ unsigned long key = tg->disptime;
+ int left = 1;
+
+ while (*node != NULL) {
+ parent = *node;
+ __tg = rb_entry_tg(parent);
+
+ if (time_before(key, __tg->disptime))
+ node = &parent->rb_left;
+ else {
+ node = &parent->rb_right;
+ left = 0;
+ }
+ }
+
+ if (left)
+ st->left = &tg->rb_node;
+
+ rb_link_node(&tg->rb_node, parent, node);
+ rb_insert_color(&tg->rb_node, &st->rb);
+}
+
+static void __throtl_enqueue_tg(struct throtl_data *td, struct throtl_grp *tg)
+{
+ struct throtl_rb_root *st = &td->tg_service_tree;
+
+ tg_service_tree_add(st, tg);
+ throtl_mark_tg_on_rr(tg);
+ st->count++;
+}
+
+static void throtl_enqueue_tg(struct throtl_data *td, struct throtl_grp *tg)
+{
+ if (!throtl_tg_on_rr(tg))
+ __throtl_enqueue_tg(td, tg);
+}
+
+static void __throtl_dequeue_tg(struct throtl_data *td, struct throtl_grp *tg)
+{
+ throtl_rb_erase(&tg->rb_node, &td->tg_service_tree);
+ throtl_clear_tg_on_rr(tg);
+}
+
+static void throtl_dequeue_tg(struct throtl_data *td, struct throtl_grp *tg)
+{
+ if (throtl_tg_on_rr(tg))
+ __throtl_dequeue_tg(td, tg);
+}
+
+static void throtl_schedule_next_dispatch(struct throtl_data *td)
+{
+ struct throtl_rb_root *st = &td->tg_service_tree;
+
+ /*
+ * If there are more bios pending, schedule more work.
+ */
+ if (!total_nr_queued(td))
+ return;
+
+ BUG_ON(!st->count);
+
+ update_min_dispatch_time(st);
+
+ if (time_before_eq(st->min_disptime, jiffies))
+ throtl_schedule_delayed_work(td->queue, 0);
+ else
+ throtl_schedule_delayed_work(td->queue,
+ (st->min_disptime - jiffies));
+}
+
+static inline void
+throtl_start_new_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
+{
+ tg->bytes_disp[rw] = 0;
+ tg->slice_start[rw] = jiffies;
+ tg->slice_end[rw] = jiffies + throtl_slice;
+ throtl_log_tg(td, tg, "[%c] new slice start=%lu end=%lu jiffies=%lu",
+ rw == READ ? 'R' : 'W', tg->slice_start[rw],
+ tg->slice_end[rw], jiffies);
+}
+
+static inline void throtl_extend_slice(struct throtl_data *td,
+ struct throtl_grp *tg, bool rw, unsigned long jiffy_end)
+{
+ tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
+ throtl_log_tg(td, tg, "[%c] extend slice start=%lu end=%lu jiffies=%lu",
+ rw == READ ? 'R' : 'W', tg->slice_start[rw],
+ tg->slice_end[rw], jiffies);
+}
+
+/* Trim the used slices and adjust slice start accordingly */
+static inline void
+throtl_trim_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
+{
+ unsigned long nr_slices, bytes_trim, time_elapsed;
+
+ BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw]));
+
+ time_elapsed = jiffies - tg->slice_start[rw];
+
+ nr_slices = time_elapsed / throtl_slice;
+
+ if (!nr_slices)
+ return;
+
+ bytes_trim = (tg->bps[rw] * throtl_slice * nr_slices)/HZ;
+
+ if (!bytes_trim)
+ return;
+
+ if (tg->bytes_disp[rw] >= bytes_trim)
+ tg->bytes_disp[rw] -= bytes_trim;
+ else
+ tg->bytes_disp[rw] = 0;
+
+ tg->slice_start[rw] += nr_slices * throtl_slice;
+
+ throtl_log_tg(td, tg, "[%c] trim slice nr=%lu bytes=%lu"
+ " start=%lu end=%lu jiffies=%lu",
+ rw == READ ? 'R' : 'W', nr_slices, bytes_trim,
+ tg->slice_start[rw], tg->slice_end[rw], jiffies);
+}
+
+/* Determine if previously allocated or extended slice is complete or not */
+static bool throtl_slice_used(struct throtl_data *td, struct throtl_grp *tg, bool rw)
+{
+ if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))
+ return 0;
+
+ return 1;
+}
+
+/*
+ * Returns whether one can dispatch a bio or not. Also returns approx number
+ * of jiffies to wait before this bio is with-in IO rate and can be dispatched
+ */
+static bool tg_may_dispatch(struct throtl_data *td, struct throtl_grp *tg,
+ struct bio *bio, unsigned long *wait)
+{
+ bool rw = bio_data_dir(bio);
+ u64 bytes_allowed, extra_bytes;
+ unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
+
+ /*
+ * Currently whole state machine of group depends on first bio
+ * queued in the group bio list. So one should not be calling
+ * this function with a different bio if there are other bios
+ * queued.
+ */
+ BUG_ON(tg->nr_queued[rw] && bio != bio_list_peek(&tg->bio_lists[rw]));
+
+ /* If tg->bps = -1, then BW is unlimited */
+ if (tg->bps[rw] == -1)
+ return 1;
+
+ /*
+ * If previous slice expired, start a new one otherwise renew/extend
+ * existing slice to make sure it is at least throtl_slice interval
+ * long since now.
+ */
+ if (throtl_slice_used(td, tg, rw))
+ throtl_start_new_slice(td, tg, rw);
+ else {
+ if (time_before(tg->slice_end[rw], jiffies + throtl_slice))
+ throtl_extend_slice(td, tg, rw, jiffies + throtl_slice);
+ }
+
+ jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
+
+ /* Slice has just started. Consider one slice interval */
+ if (!jiffy_elapsed)
+ jiffy_elapsed_rnd = throtl_slice;
+
+ jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
+
+ bytes_allowed = (tg->bps[rw] * jiffies_to_msecs(jiffy_elapsed_rnd))
+ / MSEC_PER_SEC;
+
+ if (tg->bytes_disp[rw] + bio->bi_size <= bytes_allowed) {
+ if (wait)
+ *wait = 0;
+ return 1;
+ }
+
+ /* Calc approx time to dispatch */
+ extra_bytes = tg->bytes_disp[rw] + bio->bi_size - bytes_allowed;
+ jiffy_wait = div64_u64(extra_bytes * HZ, tg->bps[rw]);
+
+ if (!jiffy_wait)
+ jiffy_wait = 1;
+
+ /*
+ * This wait time is without taking into consideration the rounding
+ * up we did. Add that time also.
+ */
+ jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed);
+
+ if (wait)
+ *wait = jiffy_wait;
+
+ if (time_before(tg->slice_end[rw], jiffies + jiffy_wait))
+ throtl_extend_slice(td, tg, rw, jiffies + jiffy_wait);
+
+ return 0;
+}
+
+static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
+{
+ bool rw = bio_data_dir(bio);
+ bool sync = bio->bi_rw & REQ_SYNC;
+
+ /* Charge the bio to the group */
+ tg->bytes_disp[rw] += bio->bi_size;
+
+ /*
+ * TODO: This will take blkg->stats_lock. Figure out a way
+ * to avoid this cost.
+ */
+ blkiocg_update_dispatch_stats(&tg->blkg, bio->bi_size, rw, sync);
+
+}
+
+static void throtl_add_bio_tg(struct throtl_data *td, struct throtl_grp *tg,
+ struct bio *bio)
+{
+ bool rw = bio_data_dir(bio);
+
+ bio_list_add(&tg->bio_lists[rw], bio);
+ /* Take a bio reference on tg */
+ throtl_ref_get_tg(tg);
+ tg->nr_queued[rw]++;
+ td->nr_queued[rw]++;
+ throtl_enqueue_tg(td, tg);
+}
+
+static void tg_update_disptime(struct throtl_data *td, struct throtl_grp *tg)
+{
+ unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
+ struct bio *bio;
+
+ if ((bio = bio_list_peek(&tg->bio_lists[READ])))
+ tg_may_dispatch(td, tg, bio, &read_wait);
+
+ if ((bio = bio_list_peek(&tg->bio_lists[WRITE])))
+ tg_may_dispatch(td, tg, bio, &write_wait);
+
+ min_wait = min(read_wait, write_wait);
+ disptime = jiffies + min_wait;
+
+ /*
+ * If group is already on active tree, then update dispatch time
+ * only if it is lesser than existing dispatch time. Otherwise
+ * always update the dispatch time
+ */
+
+ if (throtl_tg_on_rr(tg) && time_before(disptime, tg->disptime))
+ return;
+
+ /* Update dispatch time */
+ throtl_dequeue_tg(td, tg);
+ tg->disptime = disptime;
+ throtl_enqueue_tg(td, tg);
+}
+
+static void
+tg_dispatch_one_bio(struct throtl_data *td, struct throtl_grp *tg, bool rw)
+{
+ struct bio *bio;
+
+ bio = bio_list_pop(&tg->bio_lists[rw]);
+ tg->nr_queued[rw]--;
+ /* Drop bio reference on tg */
+ throtl_put_tg(tg);
+
+ BUG_ON(td->nr_queued[rw] <= 0);
+ td->nr_queued[rw]--;
+
+ throtl_charge_bio(tg, bio);
+ bio_list_add(&td->disp_list, bio);
+ td->nr_disp_list++;
+
+ throtl_trim_slice(td, tg, rw);
+}
+
+/*
+ * Enter with queue lock held spin_lock_irq(). Returns with queue lock unlocked */
+static int release_from_disp_list(struct throtl_data *td)
+{
+ struct bio *bio;
+ unsigned int nr_disp = 0;
+
+ if (!td->nr_disp_list)
+ goto out;
+
+ while (!bio_list_empty(&td->disp_list)) {
+ bio = bio_list_pop(&td->disp_list);
+ bio->bi_rw |= REQ_THROTTLED;
+ BUG_ON(td->nr_disp_list <= 0);
+ td->nr_disp_list--;
+ nr_disp++;
+ /*
+ * Drop the spin lock and submit bio.
+ */
+ spin_unlock_irq(td->queue->queue_lock);
+ generic_make_request(bio);
+ spin_lock_irq(td->queue->queue_lock);
+ }
+
+out:
+ spin_unlock_irq(td->queue->queue_lock);
+ return nr_disp;
+}
+
+static int throtl_dispatch_tg(struct throtl_data *td, struct throtl_grp *tg)
+{
+ unsigned int nr_reads = 0, nr_writes = 0;
+ unsigned int max_nr_reads = throtl_grp_quantum*3/4;
+ unsigned int max_nr_writes = throtl_grp_quantum - nr_reads;
+ struct bio *bio;
+
+ /* Try to dispatch 75% READS and 25% WRITES */
+
+ while ((bio = bio_list_peek(&tg->bio_lists[READ]))
+ && tg_may_dispatch(td, tg, bio, NULL)) {
+
+ tg_dispatch_one_bio(td, tg, bio_data_dir(bio));
+ nr_reads++;
+
+ if (nr_reads >= max_nr_reads)
+ break;
+ }
+
+ while ((bio = bio_list_peek(&tg->bio_lists[WRITE]))
+ && tg_may_dispatch(td, tg, bio, NULL)) {
+
+ tg_dispatch_one_bio(td, tg, bio_data_dir(bio));
+ nr_writes++;
+
+ if (nr_writes >= max_nr_writes)
+ break;
+ }
+
+ return nr_reads + nr_writes;
+}
+
+static int throtl_select_dispatch(struct throtl_data *td)
+{
+ unsigned int nr_disp = 0;
+ struct throtl_grp *tg;
+ struct throtl_rb_root *st = &td->tg_service_tree;
+
+ while (1) {
+ tg = throtl_rb_first(st);
+
+ if (!tg)
+ break;
+
+ if (time_before(jiffies, tg->disptime))
+ break;
+
+ throtl_dequeue_tg(td, tg);
+
+ nr_disp += throtl_dispatch_tg(td, tg);
+
+ if (tg->nr_queued[0] || tg->nr_queued[1]) {
+ tg_update_disptime(td, tg);
+ throtl_enqueue_tg(td, tg);
+ }
+
+ if (nr_disp >= throtl_quantum)
+ break;
+ }
+
+ return nr_disp;
+}
+
+/* Dispatch throttled bios. Should be called without queue lock held. */
+static int throtl_dispatch(struct request_queue *q)
+{
+ struct throtl_data *td = q->td;
+ unsigned int nr_disp = 0, temp_disp = 0;
+
+ spin_lock_irq(q->queue_lock);
+
+ if (!total_nr_queued(td))
+ goto out;
+
+ throtl_log(td, "dispatch nr_queued=%lu", total_nr_queued(td));
+
+ while(1) {
+ temp_disp = 0;
+ temp_disp = release_from_disp_list(q->td);
+ nr_disp += temp_disp;
+
+ if (nr_disp >= throtl_quantum)
+ break;
+
+ /*
+ * release_from_disp_list returns with queue lock unlocked.
+ * acquire the lock again.
+ */
+ spin_lock_irq(q->queue_lock);
+ temp_disp = throtl_select_dispatch(td);
+ if (!temp_disp)
+ break;
+ }
+
+ throtl_schedule_next_dispatch(td);
+out:
+ spin_unlock_irq(q->queue_lock);
+ /*
+ * If we dispatched some requests, unplug the queue to make sure
+ * immediate dispatch
+ */
+ if (nr_disp) {
+ throtl_log(td, "bios disp=%u", nr_disp);
+ blk_unplug(q);
+ }
+ return nr_disp;
+}
+
+void blk_throtl_work(struct work_struct *work)
+{
+ struct throtl_data *td = container_of(work, struct throtl_data,
+ throtl_work.work);
+ struct request_queue *q = td->queue;
+
+ throtl_dispatch(q);
+}
+
+/* Call with queue lock held */
+void throtl_schedule_delayed_work(struct request_queue *q, unsigned long delay)
+{
+
+ struct throtl_data *td = q->td;
+ struct delayed_work *dwork = &td->throtl_work;
+
+ if (total_nr_queued(td) > 0) {
+ /*
+ * We might have a work scheduled to be executed in future.
+ * Cancel that and schedule a new one.
+ */
+ __cancel_delayed_work(dwork);
+ kblockd_schedule_delayed_work(q, dwork, delay);
+ throtl_log(td, "schedule work. delay=%lu jiffies=%lu",
+ delay, jiffies);
+ }
+}
+EXPORT_SYMBOL(throtl_schedule_delayed_work);
+
+static void
+throtl_destroy_tg(struct throtl_data *td, struct throtl_grp *tg)
+{
+ /* Something wrong if we are trying to remove same group twice */
+ BUG_ON(hlist_unhashed(&tg->tg_node));
+
+ hlist_del_init(&tg->tg_node);
+
+ /*
+ * Put the reference taken at the time of creation so that when all
+ * queues are gone, group can be destroyed.
+ */
+ throtl_put_tg(tg);
+ td->nr_undestroyed_grps--;
+}
+
+static void throtl_release_tgs(struct throtl_data *td)
+{
+ struct hlist_node *pos, *n;
+ struct throtl_grp *tg;
+
+ hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {
+ /*
+ * If cgroup removal path got to blk_group first and removed
+ * it from cgroup list, then it will take care of destroying
+ * cfqg also.
+ */
+ if (!blkiocg_del_blkio_group(&tg->blkg))
+ throtl_destroy_tg(td, tg);
+ }
+}
+
+static void throtl_td_free(struct throtl_data *td)
+{
+ kfree(td);
+}
+
+/*
+ * Blk cgroup controller notification saying that blkio_group object is being
+ * delinked as associated cgroup object is going away. That also means that
+ * no new IO will come in this group. So get rid of this group as soon as
+ * any pending IO in the group is finished.
+ *
+ * This function is called under rcu_read_lock(). key is the rcu protected
+ * pointer. That means "key" is a valid throtl_data pointer as long as we are
+ * rcu read lock.
+ *
+ * "key" was fetched from blkio_group under blkio_cgroup->lock. That means
+ * it should not be NULL as even if queue was going away, cgroup deltion
+ * path got to it first.
+ */
+void throtl_unlink_blkio_group(void *key, struct blkio_group *blkg)
+{
+ unsigned long flags;
+ struct throtl_data *td = key;
+
+ spin_lock_irqsave(td->queue->queue_lock, flags);
+ throtl_destroy_tg(td, tg_of_blkg(blkg));
+ spin_unlock_irqrestore(td->queue->queue_lock, flags);
+}
+
+static void throtl_update_blkio_group_read_bps (struct blkio_group *blkg,
+ u64 read_bps)
+{
+ tg_of_blkg(blkg)->bps[READ] = read_bps;
+}
+
+static void throtl_update_blkio_group_write_bps (struct blkio_group *blkg,
+ u64 write_bps)
+{
+ tg_of_blkg(blkg)->bps[WRITE] = write_bps;
+}
+
+void throtl_shutdown_timer_wq(struct request_queue *q)
+{
+ struct throtl_data *td = q->td;
+
+ cancel_delayed_work_sync(&td->throtl_work);
+}
+
+static struct blkio_policy_type blkio_policy_throtl = {
+ .ops = {
+ .blkio_unlink_group_fn = throtl_unlink_blkio_group,
+ .blkio_update_group_read_bps_fn =
+ throtl_update_blkio_group_read_bps,
+ .blkio_update_group_write_bps_fn =
+ throtl_update_blkio_group_write_bps,
+ },
+};
+
+int blk_throtl_bio(struct request_queue *q, struct bio **biop)
+{
+ struct throtl_data *td = q->td;
+ struct throtl_grp *tg;
+ struct bio *bio = *biop;
+ bool rw = bio_data_dir(bio), update_disptime = true;
+
+ if (bio->bi_rw & REQ_THROTTLED) {
+ bio->bi_rw &= ~REQ_THROTTLED;
+ return 0;
+ }
+
+ /*
+ * Do not throttle barriers. Upstream work is on to get rid of
+ * hard barriers and block layer will not gurantee ordering of
+ * barrier w.r.t other bios, hence no need to flush all the
+ * queued/throttled bios.
+ */
+ if (unlikely((bio->bi_rw & REQ_HARDBARRIER)))
+ return 0;
+
+ spin_lock_irq(q->queue_lock);
+ tg = throtl_get_tg(td);
+
+ if (tg->nr_queued[rw]) {
+ /*
+ * There is already another bio queued in same dir. No
+ * need to update dispatch time.
+ */
+ update_disptime = false;
+ goto queue_bio;
+ }
+
+ /* Bio is with-in rate limit of group */
+ if (tg_may_dispatch(td, tg, bio, NULL)) {
+ throtl_charge_bio(tg, bio);
+ goto out;
+ }
+
+queue_bio:
+ throtl_log_tg(td, tg, "[%c] bio. disp=%u sz=%u bps=%llu"
+ " queued=%d/%d", rw == READ ? 'R' : 'W',
+ tg->bytes_disp[rw], bio->bi_size, tg->bps[rw],
+ tg->nr_queued[READ], tg->nr_queued[WRITE]);
+
+ throtl_add_bio_tg(q->td, tg, bio);
+ *biop = NULL;
+
+ if (update_disptime) {
+ tg_update_disptime(td, tg);
+ throtl_schedule_next_dispatch(td);
+ }
+
+out:
+ spin_unlock_irq(q->queue_lock);
+ return 0;
+}
+
+int blk_throtl_init(struct request_queue *q)
+{
+ struct throtl_data *td;
+ struct throtl_grp *tg;
+
+ td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
+ if (!td)
+ return -ENOMEM;
+
+ INIT_HLIST_HEAD(&td->tg_list);
+ td->tg_service_tree = THROTL_RB_ROOT;
+ bio_list_init(&td->disp_list);
+
+ /* Init root group */
+ tg = &td->root_tg;
+ INIT_HLIST_NODE(&tg->tg_node);
+ RB_CLEAR_NODE(&tg->rb_node);
+ bio_list_init(&tg->bio_lists[0]);
+ bio_list_init(&tg->bio_lists[1]);
+
+ /* Practically unlimited BW */
+ tg->bps[0] = tg->bps[1] = -1;
+ atomic_set(&tg->ref, 1);
+
+ INIT_DELAYED_WORK(&td->throtl_work, blk_throtl_work);
+
+ rcu_read_lock();
+ blkiocg_add_blkio_group(&blkio_root_cgroup, &tg->blkg, (void *)td,
+ 0, BLKIO_POLICY_THROTL);
+ rcu_read_unlock();
+
+ /* Attach throtl data to request queue */
+ td->queue = q;
+ q->td = td;
+ return 0;
+}
+
+void blk_throtl_exit(struct request_queue *q)
+{
+ struct throtl_data *td = q->td;
+ bool wait = false;
+
+ BUG_ON(!td);
+
+ throtl_shutdown_timer_wq(q);
+
+ spin_lock_irq(q->queue_lock);
+ throtl_release_tgs(td);
+ blkiocg_del_blkio_group(&td->root_tg.blkg);
+
+ /* If there are other groups */
+ if (td->nr_undestroyed_grps >= 1)
+ wait = true;
+
+ spin_unlock_irq(q->queue_lock);
+
+ /*
+ * Wait for tg->blkg->key accessors to exit their grace periods.
+ * Do this wait only if there are other undestroyed groups out
+ * there (other than root group). This can happen if cgroup deletion
+ * path claimed the responsibility of cleaning up a group before
+ * queue cleanup code get to the group.
+ *
+ * Do not call synchronize_rcu() unconditionally as there are drivers
+ * which create/delete request queue hundreds of times during scan/boot
+ * and synchronize_rcu() can take significant time and slow down boot.
+ */
+ if (wait)
+ synchronize_rcu();
+ throtl_td_free(td);
+}
+
+static int __init throtl_init(void)
+{
+ blkio_policy_register(&blkio_policy_throtl);
+ return 0;
+}
+
+module_init(throtl_init);
diff --git a/block/blk.h b/block/blk.h
index 6e7dc87..e836e64 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -62,8 +62,10 @@ static inline struct request *__elv_next_request(struct request_queue *q)
return rq;
}

- if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
+ if (!q->elevator->ops->elevator_dispatch_fn(q, 0)) {
+ throtl_schedule_delayed_work(q, 0);
return NULL;
+ }
}
}

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index eb4086f..8cec3a8 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -467,10 +467,14 @@ static inline bool cfq_bio_sync(struct bio *bio)
*/
static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
{
+ struct request_queue *q = cfqd->queue;
+
if (cfqd->busy_queues) {
cfq_log(cfqd, "schedule dispatch");
kblockd_schedule_work(cfqd->queue, &cfqd->unplug_work);
}
+
+ throtl_schedule_delayed_work(q, 0);
}

static int cfq_queue_empty(struct request_queue *q)
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index ca83a97..10a0c29 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -130,6 +130,8 @@ enum rq_flag_bits {
/* bio only flags */
__REQ_UNPLUG, /* unplug the immediately after submission */
__REQ_RAHEAD, /* read ahead, can fail anytime */
+ __REQ_THROTTLED, /* This bio has already been subjected to
+ * throttling rules. Don't do it again. */

/* request only flags */
__REQ_SORTED, /* elevator knows about this request */
@@ -172,6 +174,7 @@ enum rq_flag_bits {

#define REQ_UNPLUG (1 << __REQ_UNPLUG)
#define REQ_RAHEAD (1 << __REQ_RAHEAD)
+#define REQ_THROTTLED (1 << __REQ_THROTTLED)

#define REQ_SORTED (1 << __REQ_SORTED)
#define REQ_SOFTBARRIER (1 << __REQ_SOFTBARRIER)
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 2c54906..66bca1a 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -367,6 +367,11 @@ struct request_queue
#if defined(CONFIG_BLK_DEV_BSG)
struct bsg_class_device bsg_dev;
#endif
+
+#ifdef CONFIG_BLK_DEV_THROTTLING
+ /* Throttle data */
+ struct throtl_data *td;
+#endif
};

#define QUEUE_FLAG_CLUSTER 0 /* cluster several segments into 1 */
@@ -1127,6 +1132,7 @@ static inline void put_dev_sector(Sector p)

struct work_struct;
int kblockd_schedule_work(struct request_queue *q, struct work_struct *work);
+int kblockd_schedule_delayed_work(struct request_queue *q, struct delayed_work *dwork, unsigned long delay);

#ifdef CONFIG_BLK_CGROUP
/*
@@ -1170,6 +1176,24 @@ static inline uint64_t rq_io_start_time_ns(struct request *req)
}
#endif

+#ifdef CONFIG_BLK_DEV_THROTTLING
+extern int blk_throtl_init(struct request_queue *q);
+extern void blk_throtl_exit(struct request_queue *q);
+extern int blk_throtl_bio(struct request_queue *q, struct bio **bio);
+extern void throtl_schedule_delayed_work(struct request_queue *q, unsigned long delay);
+extern void throtl_shutdown_timer_wq(struct request_queue *q);
+#else /* CONFIG_BLK_DEV_THROTTLING */
+static inline int blk_throtl_bio(struct request_queue *q, struct bio **bio)
+{
+ return 0;
+}
+
+static inline int blk_throtl_init(struct request_queue *q) { return 0; }
+static inline int blk_throtl_exit(struct request_queue *q) { return 0; }
+static inline void throtl_schedule_delayed_work(struct request_queue *q, unsigned long delay) {}
+static inline void throtl_shutdown_timer_wq(struct request_queue *q) {}
+#endif /* CONFIG_BLK_DEV_THROTTLING */
+
#define MODULE_ALIAS_BLOCKDEV(major,minor) \
MODULE_ALIAS("block-major-" __stringify(major) "-" __stringify(minor))
#define MODULE_ALIAS_BLOCKDEV_MAJOR(major) \
diff --git a/init/Kconfig b/init/Kconfig
index 2de5b1c..950ba26 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -634,11 +634,14 @@ config BLK_CGROUP

Currently, CFQ IO scheduler uses it to recognize task groups and
control disk bandwidth allocation (proportional time slice allocation)
- to such task groups.
+ to such task groups. It is also used by bio throttling logic in
+ block layer to implement upper limit in IO rates on a device.

This option only enables generic Block IO controller infrastructure.
- One needs to also enable actual IO controlling logic in CFQ for it
- to take effect. (CONFIG_CFQ_GROUP_IOSCHED=y).
+ One needs to also enable actual IO controlling logic/policy. For
+ enabling proportional weight division of disk bandwidth in CFQ seti
+ CONFIG_CFQ_GROUP_IOSCHED=y and for enabling throttling policy set
+ CONFIG_BLK_THROTTLE=y.

See Documentation/cgroups/blkio-controller.txt for more information.

--
1.7.2.2


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