added simple I/O scheduler

block/Kconfig.iosched

@@ -69,6 +69,16 @@ config IOSCHED_VR
 		Requests are chosen according to SSTF with a penalty of rev_penalty
 		for switching head direction.
 
+config IOSCHED_SIO
+	tristate "Simple I/O scheduler"
+	default y
+	---help---
+	  The Simple I/O scheduler is an extremely simple scheduler,
+	  based on noop and deadline, that relies on deadlines to
+	  ensure fairness. The algorithm does not do any sorting but
+	  basic merging, trying to keep a minimum overhead. It is aimed
+	  mainly for aleatory access devices (eg: flash devices).
+
 choice
 	prompt "Default I/O scheduler"
 	default DEFAULT_CFQ
@@ -93,6 +103,9 @@ choice
 
 	config DEFAULT_VR
 		bool "V(R)" if IOSCHED_VR=y
+
+	config DEFAULT_SIO
+		bool "SIO" if IOSCHED_SIO=y
 
 endchoice
 
@@ -104,6 +117,7 @@ config DEFAULT_IOSCHED
 	default "bfq" if DEFAULT_BFQ
 	default "noop" if DEFAULT_NOOP
 	default "vr" if DEFAULT_VR
+	default "sio" if DEFAULT_SIO
 
 endmenu
 

block/Makefile

@@ -14,6 +14,7 @@ obj-$(CONFIG_IOSCHED_DEADLINE)	+= deadline-iosched.o
 obj-$(CONFIG_IOSCHED_CFQ)	+= cfq-iosched.o
 obj-$(CONFIG_IOSCHED_BFQ)	+= bfq-iosched.o
 obj-$(CONFIG_IOSCHED_VR)	+= vr-iosched.o
+obj-$(CONFIG_IOSCHED_SIO)	+= sio-iosched.o
 
 obj-$(CONFIG_BLOCK_COMPAT)	+= compat_ioctl.o
 obj-$(CONFIG_BLK_DEV_INTEGRITY)	+= blk-integrity.o

block/sio-iosched.c

@@ -0,0 +1,346 @@
+/*
+ * Simple IO scheduler
+ * Based on Noop, Deadline and V(R) IO schedulers.
+ *
+ * Copyright (C) 2010 Miguel Boton <mboton@gmail.com>
+ *
+ *
+ * This algorithm does not do any kind of sorting, as it is aimed for
+ * aleatory access devices, but it does some basic merging. We try to
+ * keep minimum overhead to achieve low latency.
+ *
+ * Asynchronous and synchronous requests are not treated separately, but
+ * we relay on deadlines to ensure fairness.
+ *
+ */
+#include <linux/blkdev.h>
+#include <linux/elevator.h>
+#include <linux/bio.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+
+enum {
+	ASYNC,
+	SYNC,
+};
+
+/* Tunables */
+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;	/* # of sequential requests treated as one
+					   by the above parameters. For throughput. */
+
+/* Elevator data */
+struct sio_data {
+	/* Request queues */
+	struct list_head fifo_list[2];
+
+	/* Attributes */
+	unsigned int batched;
+
+	/* Settings */
+	int fifo_expire[2];
+	int fifo_batch;
+};
+
+static void
+sio_merged_requests(struct request_queue *q, struct request *rq,
+		    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(&rq->queuelist) && !list_empty(&next->queuelist)) {
+		if (time_before(rq_fifo_time(next), rq_fifo_time(rq))) {
+			list_move(&rq->queuelist, &next->queuelist);
+			rq_set_fifo_time(rq, rq_fifo_time(next));
+		}
+	}
+
+	/* Delete next request */
+	rq_fifo_clear(next);
+}
+
+static void
+sio_add_request(struct request_queue *q, struct request *rq)
+{
+	struct sio_data *sd = q->elevator->elevator_data;
+	const int sync = rq_is_sync(rq);
+
+	/*
+	 * Add request to the proper fifo list and set its
+	 * expire time.
+	 */
+	rq_set_fifo_time(rq, jiffies + sd->fifo_expire[sync]);
+	list_add_tail(&rq->queuelist, &sd->fifo_list[sync]);
+}
+
+static int
+sio_queue_empty(struct request_queue *q)
+{
+	struct sio_data *sd = q->elevator->elevator_data;
+
+	/* Check if fifo lists are empty */
+	return list_empty(&sd->fifo_list[SYNC]) &&
+	       list_empty(&sd->fifo_list[ASYNC]);
+}
+
+static struct request *
+sio_expired_request(struct sio_data *sd, int sync)
+{
+	struct request *rq;
+
+	if (list_empty(&sd->fifo_list[sync]))
+		return NULL;
+
+	/* Retrieve request */
+	rq = rq_entry_fifo(sd->fifo_list[sync].next);
+
+	/* Request has expired */
+	if (time_after(jiffies, rq_fifo_time(rq)))
+		return rq;
+
+	return NULL;
+}
+
+static struct request *
+sio_choose_expired_request(struct sio_data *sd)
+{
+	struct request *sync = sio_expired_request(sd, SYNC);
+	struct request *async = sio_expired_request(sd, ASYNC);
+
+	/*
+	 * Check expired requests. Asynchronous requests have
+	 * priority over synchronous.
+	 */
+	if (sync && async)
+		return async;
+	if (sync)
+		return sync;
+
+	return async;
+
+}
+
+static struct request *
+sio_choose_request(struct sio_data *sd)
+{
+	/*
+	 * Retrieve request from available fifo list.
+	 * Synchronous requests have priority over asynchronous.
+	 */
+	if (!list_empty(&sd->fifo_list[SYNC]))
+		return rq_entry_fifo(sd->fifo_list[SYNC].next);
+
+	if (!list_empty(&sd->fifo_list[ASYNC]))
+		return rq_entry_fifo(sd->fifo_list[ASYNC].next);
+
+	return NULL;
+}
+
+static inline void
+sio_dispatch_request(struct sio_data *sd, struct request *rq)
+{
+	/*
+	 * Remove the request from the fifo list
+	 * and dispatch it.
+	 */
+	rq_fifo_clear(rq);
+	elv_dispatch_add_tail(rq->q, rq);
+
+	sd->batched++;
+}
+
+static int
+sio_dispatch_requests(struct request_queue *q, int force)
+{
+	struct sio_data *sd = q->elevator->elevator_data;
+	struct request *rq = NULL;
+
+	/*
+	 * Retrieve any expired request after a batch of
+	 * sequential requests.
+	 */
+	if (sd->batched > sd->fifo_batch) {
+		sd->batched = 0;
+		rq = sio_choose_expired_request(sd);
+	}
+
+	/* Retrieve request */
+	if (!rq) {
+		rq = sio_choose_request(sd);
+		if (!rq)
+			return 0;
+	}
+
+	/* Dispatch request */
+	sio_dispatch_request(sd, rq);
+
+	return 1;
+}
+
+static struct request *
+sio_former_request(struct request_queue *q, struct request *rq)
+{
+	struct sio_data *sd = q->elevator->elevator_data;
+	const int sync = rq_is_sync(rq);
+
+	if (rq->queuelist.prev == &sd->fifo_list[sync])
+		return NULL;
+
+	/* Return former request */
+	return list_entry(rq->queuelist.prev, struct request, queuelist);
+}
+
+static struct request *
+sio_latter_request(struct request_queue *q, struct request *rq)
+{
+	struct sio_data *sd = q->elevator->elevator_data;
+	const int sync = rq_is_sync(rq);
+
+	if (rq->queuelist.next == &sd->fifo_list[sync])
+		return NULL;
+
+	/* Return latter request */
+	return list_entry(rq->queuelist.next, struct request, queuelist);
+}
+
+static void *
+sio_init_queue(struct request_queue *q)
+{
+	struct sio_data *sd;
+
+	/* Allocate structure */
+	sd = kmalloc_node(sizeof(*sd), GFP_KERNEL, q->node);
+	if (!sd)
+		return NULL;
+
+	/* Initialize fifo lists */
+	INIT_LIST_HEAD(&sd->fifo_list[SYNC]);
+	INIT_LIST_HEAD(&sd->fifo_list[ASYNC]);
+
+	/* Initialize data */
+	sd->batched = 0;
+	sd->fifo_expire[SYNC] = sync_expire;
+	sd->fifo_expire[ASYNC] = async_expire;
+	sd->fifo_batch = fifo_batch;
+
+	return sd;
+}
+
+static void
+sio_exit_queue(struct elevator_queue *e)
+{
+	struct sio_data *sd = e->elevator_data;
+
+	BUG_ON(!list_empty(&sd->fifo_list[SYNC]));
+	BUG_ON(!list_empty(&sd->fifo_list[ASYNC]));
+
+	/* Free structure */
+	kfree(sd);
+}
+
+/*
+ * sysfs code
+ */
+
+static ssize_t
+sio_var_show(int var, char *page)
+{
+	return sprintf(page, "%d\n", var);
+}
+
+static ssize_t
+sio_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 sio_data *sd = e->elevator_data;			\
+	int __data = __VAR;						\
+	if (__CONV)							\
+		__data = jiffies_to_msecs(__data);			\
+	return sio_var_show(__data, (page));			\
+}
+SHOW_FUNCTION(sio_sync_expire_show, sd->fifo_expire[SYNC], 1);
+SHOW_FUNCTION(sio_async_expire_show, sd->fifo_expire[ASYNC], 1);
+SHOW_FUNCTION(sio_fifo_batch_show, sd->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 sio_data *sd = e->elevator_data;			\
+	int __data;							\
+	int ret = sio_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(sio_sync_expire_store, &sd->fifo_expire[SYNC], 0, INT_MAX, 1);
+STORE_FUNCTION(sio_async_expire_store, &sd->fifo_expire[ASYNC], 0, INT_MAX, 1);
+STORE_FUNCTION(sio_fifo_batch_store, &sd->fifo_batch, 0, INT_MAX, 0);
+#undef STORE_FUNCTION
+
+#define DD_ATTR(name) \
+	__ATTR(name, S_IRUGO|S_IWUSR, sio_##name##_show, \
+				      sio_##name##_store)
+
+static struct elv_fs_entry sio_attrs[] = {
+	DD_ATTR(sync_expire),
+	DD_ATTR(async_expire),
+	DD_ATTR(fifo_batch),
+	__ATTR_NULL
+};
+
+static struct elevator_type iosched_sio = {
+	.ops = {
+		.elevator_merge_req_fn		= sio_merged_requests,
+		.elevator_dispatch_fn		= sio_dispatch_requests,
+		.elevator_add_req_fn		= sio_add_request,
+		.elevator_queue_empty_fn	= sio_queue_empty,
+		.elevator_former_req_fn		= sio_former_request,
+		.elevator_latter_req_fn		= sio_latter_request,
+		.elevator_init_fn		= sio_init_queue,
+		.elevator_exit_fn		= sio_exit_queue,
+	},
+
+	.elevator_attrs = sio_attrs,
+	.elevator_name = "sio",
+	.elevator_owner = THIS_MODULE,
+};
+
+static int __init sio_init(void)
+{
+	/* Register elevator */
+	elv_register(&iosched_sio);
+
+	return 0;
+}
+
+static void __exit sio_exit(void)
+{
+	/* Unregister elevator */
+	elv_unregister(&iosched_sio);
+}
+
+module_init(sio_init);
+module_exit(sio_exit);
+
+MODULE_AUTHOR("Miguel Boton");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Simple IO scheduler");