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Subject[PATCH 7/8] mq-deadline: add blk-mq adaptation of the deadline IO scheduler
Date
This is basically identical to deadline-iosched, except it registers
as a MQ capable scheduler. This is still a single queue design.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
block/Kconfig.iosched | 6 +
block/Makefile | 1 +
block/mq-deadline.c | 649 ++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 656 insertions(+)
create mode 100644 block/mq-deadline.c

diff --git a/block/Kconfig.iosched b/block/Kconfig.iosched
index 421bef9c4c48..490ef2850fae 100644
--- a/block/Kconfig.iosched
+++ b/block/Kconfig.iosched
@@ -32,6 +32,12 @@ config IOSCHED_CFQ

This is the default I/O scheduler.

+config MQ_IOSCHED_DEADLINE
+ tristate "MQ deadline I/O scheduler"
+ default y
+ ---help---
+ MQ version of the deadline IO scheduler.
+
config CFQ_GROUP_IOSCHED
bool "CFQ Group Scheduling support"
depends on IOSCHED_CFQ && BLK_CGROUP
diff --git a/block/Makefile b/block/Makefile
index 2eee9e1bb6db..3ee0abd7205a 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -18,6 +18,7 @@ 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
+obj-$(CONFIG_MQ_IOSCHED_DEADLINE) += mq-deadline.o

obj-$(CONFIG_BLOCK_COMPAT) += compat_ioctl.o
obj-$(CONFIG_BLK_CMDLINE_PARSER) += cmdline-parser.o
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
new file mode 100644
index 000000000000..3cb9de21ab21
--- /dev/null
+++ b/block/mq-deadline.c
@@ -0,0 +1,649 @@
+/*
+ * MQ Deadline i/o scheduler - adaptation of the legacy deadline scheduler,
+ * for the blk-mq scheduling framework
+ *
+ * Copyright (C) 2016 Jens Axboe <axboe@kernel.dk>
+ */
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/blkdev.h>
+#include <linux/blk-mq.h>
+#include <linux/elevator.h>
+#include <linux/bio.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/compiler.h>
+#include <linux/rbtree.h>
+#include <linux/sbitmap.h>
+
+#include "blk.h"
+#include "blk-mq.h"
+#include "blk-mq-tag.h"
+#include "blk-mq-sched.h"
+
+static unsigned int queue_depth = 256;
+module_param(queue_depth, uint, 0644);
+MODULE_PARM_DESC(queue_depth, "Use this value as the scheduler queue depth");
+
+/*
+ * See Documentation/block/deadline-iosched.txt
+ */
+static const int read_expire = HZ / 2; /* max time before a read is submitted. */
+static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
+static const int writes_starved = 2; /* max times reads can starve a write */
+static const int fifo_batch = 16; /* # of sequential requests treated as one
+ by the above parameters. For throughput. */
+
+struct deadline_data {
+ /*
+ * run time data
+ */
+
+ /*
+ * requests (deadline_rq s) are present on both sort_list and fifo_list
+ */
+ struct rb_root sort_list[2];
+ struct list_head fifo_list[2];
+
+ /*
+ * next in sort order. read, write or both are NULL
+ */
+ struct request *next_rq[2];
+ unsigned int batching; /* number of sequential requests made */
+ unsigned int starved; /* times reads have starved writes */
+
+ /*
+ * settings that change how the i/o scheduler behaves
+ */
+ int fifo_expire[2];
+ int fifo_batch;
+ int writes_starved;
+ int front_merges;
+
+ spinlock_t lock;
+ struct list_head dispatch;
+ struct blk_mq_tags *tags;
+ atomic_t wait_index;
+};
+
+static inline struct rb_root *
+deadline_rb_root(struct deadline_data *dd, struct request *rq)
+{
+ return &dd->sort_list[rq_data_dir(rq)];
+}
+
+/*
+ * get the request after `rq' in sector-sorted order
+ */
+static inline struct request *
+deadline_latter_request(struct request *rq)
+{
+ struct rb_node *node = rb_next(&rq->rb_node);
+
+ if (node)
+ return rb_entry_rq(node);
+
+ return NULL;
+}
+
+static void
+deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
+{
+ struct rb_root *root = deadline_rb_root(dd, rq);
+
+ elv_rb_add(root, rq);
+}
+
+static inline void
+deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
+{
+ const int data_dir = rq_data_dir(rq);
+
+ if (dd->next_rq[data_dir] == rq)
+ dd->next_rq[data_dir] = deadline_latter_request(rq);
+
+ elv_rb_del(deadline_rb_root(dd, rq), rq);
+}
+
+/*
+ * remove rq from rbtree and fifo.
+ */
+static void deadline_remove_request(struct request_queue *q, struct request *rq)
+{
+ struct deadline_data *dd = q->elevator->elevator_data;
+
+ list_del_init(&rq->queuelist);
+
+ /*
+ * We might not be on the rbtree, if we are doing an insert merge
+ */
+ if (!RB_EMPTY_NODE(&rq->rb_node))
+ deadline_del_rq_rb(dd, rq);
+
+ elv_rqhash_del(q, rq);
+ if (q->last_merge == rq)
+ q->last_merge = NULL;
+}
+
+static void dd_request_merged(struct request_queue *q, struct request *req,
+ int type)
+{
+ struct deadline_data *dd = q->elevator->elevator_data;
+
+ /*
+ * if the merge was a front merge, we need to reposition request
+ */
+ if (type == ELEVATOR_FRONT_MERGE) {
+ elv_rb_del(deadline_rb_root(dd, req), req);
+ deadline_add_rq_rb(dd, req);
+ }
+}
+
+static void dd_merged_requests(struct request_queue *q, struct request *req,
+ struct request *next)
+{
+ /*
+ * if next expires before rq, assign its expire time to rq
+ * and move into next position (next will be deleted) in fifo
+ */
+ if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
+ if (time_before((unsigned long)next->fifo_time,
+ (unsigned long)req->fifo_time)) {
+ list_move(&req->queuelist, &next->queuelist);
+ req->fifo_time = next->fifo_time;
+ }
+ }
+
+ /*
+ * kill knowledge of next, this one is a goner
+ */
+ deadline_remove_request(q, next);
+}
+
+/*
+ * move an entry to dispatch queue
+ */
+static void
+deadline_move_request(struct deadline_data *dd, struct request *rq)
+{
+ const int data_dir = rq_data_dir(rq);
+
+ dd->next_rq[READ] = NULL;
+ dd->next_rq[WRITE] = NULL;
+ dd->next_rq[data_dir] = deadline_latter_request(rq);
+
+ /*
+ * take it off the sort and fifo list
+ */
+ deadline_remove_request(rq->q, rq);
+}
+
+/*
+ * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
+ * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
+ */
+static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
+{
+ struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
+
+ /*
+ * rq is expired!
+ */
+ if (time_after_eq(jiffies, (unsigned long)rq->fifo_time))
+ return 1;
+
+ return 0;
+}
+
+/*
+ * deadline_dispatch_requests selects the best request according to
+ * read/write expire, fifo_batch, etc
+ */
+static struct request *__dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
+{
+ struct deadline_data *dd = hctx->queue->elevator->elevator_data;
+ struct request *rq;
+ bool reads, writes;
+ int data_dir;
+
+ spin_lock(&dd->lock);
+
+ if (!list_empty(&dd->dispatch)) {
+ rq = list_first_entry(&dd->dispatch, struct request, queuelist);
+ list_del_init(&rq->queuelist);
+ goto done;
+ }
+
+ reads = !list_empty(&dd->fifo_list[READ]);
+ writes = !list_empty(&dd->fifo_list[WRITE]);
+
+ /*
+ * batches are currently reads XOR writes
+ */
+ if (dd->next_rq[WRITE])
+ rq = dd->next_rq[WRITE];
+ else
+ rq = dd->next_rq[READ];
+
+ if (rq && dd->batching < dd->fifo_batch)
+ /* we have a next request are still entitled to batch */
+ goto dispatch_request;
+
+ /*
+ * at this point we are not running a batch. select the appropriate
+ * data direction (read / write)
+ */
+
+ if (reads) {
+ BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
+
+ if (writes && (dd->starved++ >= dd->writes_starved))
+ goto dispatch_writes;
+
+ data_dir = READ;
+
+ goto dispatch_find_request;
+ }
+
+ /*
+ * there are either no reads or writes have been starved
+ */
+
+ if (writes) {
+dispatch_writes:
+ BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
+
+ dd->starved = 0;
+
+ data_dir = WRITE;
+
+ goto dispatch_find_request;
+ }
+
+ spin_unlock(&dd->lock);
+ return NULL;
+
+dispatch_find_request:
+ /*
+ * we are not running a batch, find best request for selected data_dir
+ */
+ if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) {
+ /*
+ * A deadline has expired, the last request was in the other
+ * direction, or we have run out of higher-sectored requests.
+ * Start again from the request with the earliest expiry time.
+ */
+ rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
+ } else {
+ /*
+ * The last req was the same dir and we have a next request in
+ * sort order. No expired requests so continue on from here.
+ */
+ rq = dd->next_rq[data_dir];
+ }
+
+ dd->batching = 0;
+
+dispatch_request:
+ /*
+ * rq is the selected appropriate request.
+ */
+ dd->batching++;
+ deadline_move_request(dd, rq);
+done:
+ rq->rq_flags |= RQF_STARTED;
+ spin_unlock(&dd->lock);
+ return rq;
+}
+
+static void dd_dispatch_requests(struct blk_mq_hw_ctx *hctx,
+ struct list_head *rq_list)
+{
+ blk_mq_sched_dispatch_shadow_requests(hctx, rq_list, __dd_dispatch_request);
+}
+
+static void dd_exit_queue(struct elevator_queue *e)
+{
+ struct deadline_data *dd = e->elevator_data;
+
+ BUG_ON(!list_empty(&dd->fifo_list[READ]));
+ BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
+
+ blk_mq_sched_free_requests(dd->tags);
+ kfree(dd);
+}
+
+/*
+ * initialize elevator private data (deadline_data).
+ */
+static int dd_init_queue(struct request_queue *q, struct elevator_type *e)
+{
+ struct deadline_data *dd;
+ struct elevator_queue *eq;
+
+ eq = elevator_alloc(q, e);
+ if (!eq)
+ return -ENOMEM;
+
+ dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
+ if (!dd) {
+ kobject_put(&eq->kobj);
+ return -ENOMEM;
+ }
+ eq->elevator_data = dd;
+
+ dd->tags = blk_mq_sched_alloc_requests(queue_depth, q->node);
+ if (!dd->tags) {
+ kfree(dd);
+ kobject_put(&eq->kobj);
+ return -ENOMEM;
+ }
+
+ INIT_LIST_HEAD(&dd->fifo_list[READ]);
+ INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
+ dd->sort_list[READ] = RB_ROOT;
+ dd->sort_list[WRITE] = RB_ROOT;
+ dd->fifo_expire[READ] = read_expire;
+ dd->fifo_expire[WRITE] = write_expire;
+ dd->writes_starved = writes_starved;
+ dd->front_merges = 1;
+ dd->fifo_batch = fifo_batch;
+ spin_lock_init(&dd->lock);
+ INIT_LIST_HEAD(&dd->dispatch);
+ atomic_set(&dd->wait_index, 0);
+
+ q->elevator = eq;
+ return 0;
+}
+
+static int dd_request_merge(struct request_queue *q, struct request **rq,
+ struct bio *bio)
+{
+ struct deadline_data *dd = q->elevator->elevator_data;
+ sector_t sector = bio_end_sector(bio);
+ struct request *__rq;
+
+ if (!dd->front_merges)
+ return ELEVATOR_NO_MERGE;
+
+ __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
+ if (__rq) {
+ BUG_ON(sector != blk_rq_pos(__rq));
+
+ if (elv_bio_merge_ok(__rq, bio)) {
+ *rq = __rq;
+ return ELEVATOR_FRONT_MERGE;
+ }
+ }
+
+ return ELEVATOR_NO_MERGE;
+}
+
+static bool dd_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio)
+{
+ struct request_queue *q = hctx->queue;
+ struct deadline_data *dd = q->elevator->elevator_data;
+ int ret;
+
+ spin_lock(&dd->lock);
+ ret = blk_mq_sched_try_merge(q, bio);
+ spin_unlock(&dd->lock);
+
+ return ret;
+}
+
+/*
+ * add rq to rbtree and fifo
+ */
+static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
+ bool at_head)
+{
+ struct request_queue *q = hctx->queue;
+ struct deadline_data *dd = q->elevator->elevator_data;
+ const int data_dir = rq_data_dir(rq);
+
+ if (blk_mq_sched_try_insert_merge(q, rq))
+ return;
+
+ blk_mq_sched_request_inserted(rq);
+
+ /*
+ * If we're trying to insert a real request, just send it directly
+ * to the hardware dispatch list. This only happens for a requeue,
+ * or FUA/FLUSH requests.
+ */
+ if (!blk_mq_sched_rq_is_shadow(rq)) {
+ spin_lock(&hctx->lock);
+ list_add_tail(&rq->queuelist, &hctx->dispatch);
+ spin_unlock(&hctx->lock);
+ return;
+ }
+
+ if (at_head || rq->cmd_type != REQ_TYPE_FS) {
+ if (at_head)
+ list_add(&rq->queuelist, &dd->dispatch);
+ else
+ list_add_tail(&rq->queuelist, &dd->dispatch);
+ } else {
+ deadline_add_rq_rb(dd, rq);
+
+ if (rq_mergeable(rq)) {
+ elv_rqhash_add(q, rq);
+ if (!q->last_merge)
+ q->last_merge = rq;
+ }
+
+ /*
+ * set expire time and add to fifo list
+ */
+ rq->fifo_time = jiffies + dd->fifo_expire[data_dir];
+ list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
+ }
+}
+
+static void dd_insert_requests(struct blk_mq_hw_ctx *hctx,
+ struct list_head *list, bool at_head)
+{
+ struct request_queue *q = hctx->queue;
+ struct deadline_data *dd = q->elevator->elevator_data;
+
+ spin_lock(&dd->lock);
+ while (!list_empty(list)) {
+ struct request *rq;
+
+ rq = list_first_entry(list, struct request, queuelist);
+ list_del_init(&rq->queuelist);
+ dd_insert_request(hctx, rq, at_head);
+ }
+ spin_unlock(&dd->lock);
+}
+
+static struct request *dd_get_request(struct request_queue *q, unsigned int op,
+ struct blk_mq_alloc_data *data)
+{
+ struct deadline_data *dd = q->elevator->elevator_data;
+ struct request *rq;
+
+ /*
+ * The flush machinery intercepts before we insert the request. As
+ * a work-around, just hand it back a real request.
+ */
+ if (unlikely(op & (REQ_PREFLUSH | REQ_FUA)))
+ rq = __blk_mq_alloc_request(data, op);
+ else {
+ rq = blk_mq_sched_alloc_shadow_request(q, data, dd->tags, &dd->wait_index);
+ if (rq)
+ blk_mq_rq_ctx_init(q, data->ctx, rq, op);
+ }
+
+ return rq;
+}
+
+static bool dd_put_request(struct request *rq)
+{
+ /*
+ * If it's a real request, we just have to free it. For a shadow
+ * request, we should only free it if we haven't started it. A
+ * started request is mapped to a real one, and the real one will
+ * free it. We can get here with request merges, since we then
+ * free the request before we start/issue it.
+ */
+ if (!blk_mq_sched_rq_is_shadow(rq))
+ return false;
+
+ if (!(rq->rq_flags & RQF_STARTED)) {
+ struct request_queue *q = rq->q;
+ struct deadline_data *dd = q->elevator->elevator_data;
+
+ /*
+ * IO completion would normally do this, but if we merge
+ * and free before we issue the request, drop both the
+ * tag and queue ref
+ */
+ blk_mq_sched_free_shadow_request(dd->tags, rq);
+ blk_queue_exit(q);
+ }
+
+ return true;
+}
+
+static void dd_completed_request(struct blk_mq_hw_ctx *hctx, struct request *rq)
+{
+ struct request *sched_rq = rq->end_io_data;
+
+ /*
+ * sched_rq can be NULL, if we haven't setup the shadow yet
+ * because we failed getting one.
+ */
+ if (sched_rq) {
+ struct deadline_data *dd = hctx->queue->elevator->elevator_data;
+
+ blk_mq_sched_free_shadow_request(dd->tags, sched_rq);
+ blk_mq_start_stopped_hw_queue(hctx, true);
+ }
+}
+
+static bool dd_has_work(struct blk_mq_hw_ctx *hctx)
+{
+ struct deadline_data *dd = hctx->queue->elevator->elevator_data;
+
+ return !list_empty_careful(&dd->dispatch) ||
+ !list_empty_careful(&dd->fifo_list[0]) ||
+ !list_empty_careful(&dd->fifo_list[1]);
+}
+
+/*
+ * sysfs parts below
+ */
+static ssize_t
+deadline_var_show(int var, char *page)
+{
+ return sprintf(page, "%d\n", var);
+}
+
+static ssize_t
+deadline_var_store(int *var, const char *page, size_t count)
+{
+ char *p = (char *) page;
+
+ *var = simple_strtol(p, &p, 10);
+ return count;
+}
+
+#define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
+static ssize_t __FUNC(struct elevator_queue *e, char *page) \
+{ \
+ struct deadline_data *dd = e->elevator_data; \
+ int __data = __VAR; \
+ if (__CONV) \
+ __data = jiffies_to_msecs(__data); \
+ return deadline_var_show(__data, (page)); \
+}
+SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
+SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
+SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
+SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
+SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
+#undef SHOW_FUNCTION
+
+#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
+static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
+{ \
+ struct deadline_data *dd = e->elevator_data; \
+ int __data; \
+ int ret = deadline_var_store(&__data, (page), count); \
+ if (__data < (MIN)) \
+ __data = (MIN); \
+ else if (__data > (MAX)) \
+ __data = (MAX); \
+ if (__CONV) \
+ *(__PTR) = msecs_to_jiffies(__data); \
+ else \
+ *(__PTR) = __data; \
+ return ret; \
+}
+STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
+STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
+STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
+STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
+STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
+#undef STORE_FUNCTION
+
+#define DD_ATTR(name) \
+ __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
+ deadline_##name##_store)
+
+static struct elv_fs_entry deadline_attrs[] = {
+ DD_ATTR(read_expire),
+ DD_ATTR(write_expire),
+ DD_ATTR(writes_starved),
+ DD_ATTR(front_merges),
+ DD_ATTR(fifo_batch),
+ __ATTR_NULL
+};
+
+static struct elevator_type mq_deadline = {
+ .ops.mq = {
+ .get_request = dd_get_request,
+ .put_request = dd_put_request,
+ .insert_requests = dd_insert_requests,
+ .dispatch_requests = dd_dispatch_requests,
+ .completed_request = dd_completed_request,
+ .next_request = elv_rb_latter_request,
+ .former_request = elv_rb_former_request,
+ .bio_merge = dd_bio_merge,
+ .request_merge = dd_request_merge,
+ .requests_merged = dd_merged_requests,
+ .request_merged = dd_request_merged,
+ .has_work = dd_has_work,
+ .init_sched = dd_init_queue,
+ .exit_sched = dd_exit_queue,
+ },
+
+ .uses_mq = true,
+ .elevator_attrs = deadline_attrs,
+ .elevator_name = "mq-deadline",
+ .elevator_owner = THIS_MODULE,
+};
+
+static int __init deadline_init(void)
+{
+ if (!queue_depth) {
+ pr_err("mq-deadline: queue depth must be > 0\n");
+ return -EINVAL;
+ }
+ return elv_register(&mq_deadline);
+}
+
+static void __exit deadline_exit(void)
+{
+ elv_unregister(&mq_deadline);
+}
+
+module_init(deadline_init);
+module_exit(deadline_exit);
+
+MODULE_AUTHOR("Jens Axboe");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("MQ deadline IO scheduler");
--
2.7.4
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