--- /dev/null
+/*
+ * Zen IO scheduler
+ * Primarily based on Noop, deadline, and SIO IO schedulers.
+ *
+ * Copyright (C) 2012 Brandon Berhent <bbedward@gmail.com>
+ * (C) 2014 LoungeKatt <twistedumbrella@gmail.com>
+ * (c) 2015 Fixes to stop crashing on 3.10 by Matthew Alex <matthewalex@outlook.com>
+ * (c) 2016 POrt and fixes for Linux 3.18 by engstk <eng.stk@sapo.pt>
+ *
+ * FCFS, dispatches are back-inserted, deadlines ensure fairness.
+ * Should work best with devices where there is no travel delay.
+ */
+#include <linux/blkdev.h>
+#include <linux/elevator.h>
+#include <linux/bio.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+
+enum zen_data_dir { ASYNC, SYNC };
+
+static const int sync_expire = HZ / 2; /* max time before a sync is submitted. */
+static const int async_expire = 5 * HZ; /* ditto for async, these limits are SOFT! */
+static const int fifo_batch = 16;
+
+struct zen_data {
+ /* Runtime Data */
+ /* Requests are only present on fifo_list */
+ struct list_head fifo_list[2];
+
+ unsigned int batching; /* number of sequential requests made */
+
+ /* tunables */
+ int fifo_expire[2];
+ int fifo_batch;
+};
+
+static inline struct zen_data *
+zen_get_data(struct request_queue *q) {
+ return q->elevator->elevator_data;
+}
+
+static void zen_dispatch(struct zen_data *, struct request *);
+
+static void
+zen_merged_requests(struct request_queue *q, struct request *req,
+ struct request *next)
+{
+ /*
+ * if next expires before rq, assign its expire time to arq
+ * and move into next position (next will be deleted) in fifo
+ */
+ if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
+ if (time_before(next->fifo_time, req->fifo_time)) {
+ list_move(&req->queuelist, &next->queuelist);
+ req->fifo_time = next->fifo_time;
+ }
+ }
+
+ /* next request is gone */
+ rq_fifo_clear(next);
+}
+
+static void zen_add_request(struct request_queue *q, struct request *rq)
+{
+ struct zen_data *zdata = zen_get_data(q);
+ const int sync = rq_is_sync(rq);
+
+ if (zdata->fifo_expire[sync]) {
+ rq->fifo_time = jiffies + zdata->fifo_expire[sync];
+ list_add_tail(&rq->queuelist, &zdata->fifo_list[sync]);
+ }
+}
+
+static void zen_dispatch(struct zen_data *zdata, struct request *rq)
+{
+ /* Remove request from list and dispatch it */
+ rq_fifo_clear(rq);
+ elv_dispatch_add_tail(rq->q, rq);
+
+ /* Increment # of sequential requests */
+ zdata->batching++;
+}
+
+/*
+ * get the first expired request in direction ddir
+ */
+static struct request *
+zen_expired_request(struct zen_data *zdata, int ddir)
+{
+ struct request *rq;
+
+ if (list_empty(&zdata->fifo_list[ddir]))
+ return NULL;
+
+ rq = rq_entry_fifo(zdata->fifo_list[ddir].next);
+ if (time_after_eq(jiffies, rq->fifo_time))
+ return rq;
+
+ return NULL;
+}
+
+/*
+ * zen_check_fifo returns 0 if there are no expired requests on the fifo,
+ * otherwise it returns the next expired request
+ */
+static struct request *
+zen_check_fifo(struct zen_data *zdata)
+{
+ struct request *rq_sync = zen_expired_request(zdata, SYNC);
+ struct request *rq_async = zen_expired_request(zdata, ASYNC);
+
+ if (rq_async && rq_sync) {
+ if (time_after(rq_async->fifo_time, rq_sync->fifo_time))
+ return rq_sync;
+ } else if (rq_sync) {
+ return rq_sync;
+ } else if (rq_async) {
+ return rq_async;
+ }
+
+ return 0;
+}
+
+static struct request *
+zen_choose_request(struct zen_data *zdata)
+{
+ /*
+ * Retrieve request from available fifo list.
+ * Synchronous requests have priority over asynchronous.
+ */
+ if (!list_empty(&zdata->fifo_list[SYNC]))
+ return rq_entry_fifo(zdata->fifo_list[SYNC].next);
+ if (!list_empty(&zdata->fifo_list[ASYNC]))
+ return rq_entry_fifo(zdata->fifo_list[ASYNC].next);
+
+ return NULL;
+}
+
+static int zen_dispatch_requests(struct request_queue *q, int force)
+{
+ struct zen_data *zdata = zen_get_data(q);
+ struct request *rq = NULL;
+
+ /* Check for and issue expired requests */
+ if (zdata->batching > zdata->fifo_batch) {
+ zdata->batching = 0;
+ rq = zen_check_fifo(zdata);
+ }
+
+ if (!rq) {
+ rq = zen_choose_request(zdata);
+ if (!rq)
+ return 0;
+ }
+
+ zen_dispatch(zdata, rq);
+
+ return 1;
+}
+
+static int zen_init_queue(struct request_queue *q, struct elevator_type *e)
+{
+ struct zen_data *zdata;
+ struct elevator_queue *eq;
+
+ eq = elevator_alloc(q, e);
+ if (!eq)
+ return -ENOMEM;
+
+ zdata = kmalloc_node(sizeof(*zdata), GFP_KERNEL, q->node);
+ if (!zdata) {
+ kobject_put(&eq->kobj);
+ return -ENOMEM;
+ }
+ eq->elevator_data = zdata;
+
+
+ spin_lock_irq(q->queue_lock);
+ q->elevator = eq;
+ spin_unlock_irq(q->queue_lock);
+
+ INIT_LIST_HEAD(&zdata->fifo_list[SYNC]);
+ INIT_LIST_HEAD(&zdata->fifo_list[ASYNC]);
+ zdata->fifo_expire[SYNC] = sync_expire;
+ zdata->fifo_expire[ASYNC] = async_expire;
+ zdata->fifo_batch = fifo_batch;
+ return 0;
+}
+
+static void zen_exit_queue(struct elevator_queue *e)
+{
+ struct zen_data *zdata = e->elevator_data;
+
+ BUG_ON(!list_empty(&zdata->fifo_list[SYNC]));
+ BUG_ON(!list_empty(&zdata->fifo_list[ASYNC]));
+ kfree(zdata);
+}
+
+/* Sysfs */
+static ssize_t
+zen_var_show(int var, char *page)
+{
+ return sprintf(page, "%d\n", var);
+}
+
+static ssize_t
+zen_var_store(int *var, const char *page, size_t count)
+{
+ *var = simple_strtol(page, NULL, 10);
+ return count;
+}
+
+#define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
+static ssize_t __FUNC(struct elevator_queue *e, char *page) \
+{ \
+ struct zen_data *zdata = e->elevator_data; \
+ int __data = __VAR; \
+ if (__CONV) \
+ __data = jiffies_to_msecs(__data); \
+ return zen_var_show(__data, (page)); \
+}
+SHOW_FUNCTION(zen_sync_expire_show, zdata->fifo_expire[SYNC], 1);
+SHOW_FUNCTION(zen_async_expire_show, zdata->fifo_expire[ASYNC], 1);
+SHOW_FUNCTION(zen_fifo_batch_show, zdata->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 zen_data *zdata = e->elevator_data; \
+ int __data; \
+ int ret = zen_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(zen_sync_expire_store, &zdata->fifo_expire[SYNC], 0, INT_MAX, 1);
+STORE_FUNCTION(zen_async_expire_store, &zdata->fifo_expire[ASYNC], 0, INT_MAX, 1);
+STORE_FUNCTION(zen_fifo_batch_store, &zdata->fifo_batch, 0, INT_MAX, 0);
+#undef STORE_FUNCTION
+
+#define DD_ATTR(name) \
+ __ATTR(name, S_IRUGO|S_IWUSR, zen_##name##_show, \
+ zen_##name##_store)
+
+static struct elv_fs_entry zen_attrs[] = {
+ DD_ATTR(sync_expire),
+ DD_ATTR(async_expire),
+ DD_ATTR(fifo_batch),
+ __ATTR_NULL
+};
+
+static struct elevator_type iosched_zen = {
+ .ops = {
+ .elevator_merge_req_fn = zen_merged_requests,
+ .elevator_dispatch_fn = zen_dispatch_requests,
+ .elevator_add_req_fn = zen_add_request,
+ .elevator_former_req_fn = elv_rb_former_request,
+ .elevator_latter_req_fn = elv_rb_latter_request,
+ .elevator_init_fn = zen_init_queue,
+ .elevator_exit_fn = zen_exit_queue,
+ },
+ .elevator_attrs = zen_attrs,
+ .elevator_name = "zen",
+ .elevator_owner = THIS_MODULE,
+};
+
+static int __init zen_init(void)
+{
+ return elv_register(&iosched_zen);
+}
+
+static void __exit zen_exit(void)
+{
+ elv_unregister(&iosched_zen);
+}
+
+module_init(zen_init);
+module_exit(zen_exit);
+
+
+MODULE_AUTHOR("Brandon Berhent");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Zen IO scheduler");
+MODULE_VERSION("1.1");
+
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