Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with
or
.
Download ZIP
Browse files

BLOCK : Add Simple I/O scheduler

  • Loading branch information...
commit 2494b4c60d317ca11ffce40f46ef00ac4c5a0c3c 1 parent 8be83ab
@burstlam burstlam authored Lalit Maganti committed
Showing with 361 additions and 0 deletions.
  1. +14 −0 block/Kconfig.iosched
  2. +1 −0  block/Makefile
  3. +346 −0 block/sio-iosched.c
View
14 block/Kconfig.iosched
@@ -72,6 +72,16 @@ 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
@@ -94,6 +104,9 @@ choice
config DEFAULT_VR
bool "V(R)" if IOSCHED_VR=y
+ config DEFAULT_SIO
+ bool "SIO" if IOSCHED_SIO=y
+
endchoice
config DEFAULT_IOSCHED
@@ -103,6 +116,7 @@ config DEFAULT_IOSCHED
default "bfq" if DEFAULT_BFQ
default "noop" if DEFAULT_NOOP
default "vr" if DEFAULT_VR
+ default "sio" if DEFAULT_SIO
endmenu
View
1  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
View
346 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");
Please sign in to comment.
Something went wrong with that request. Please try again.