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Subject[PATCH 10/21] block: elevator selection and pinning
Provide an block queue init function that allows to set an elevator. And a 
function to pin the current elevator.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Daniel Phillips <phillips@google.com>
CC: Jens Axboe <axboe@suse.de>
CC: Pavel Machek <pavel@ucw.cz>
---
block/elevator.c | 56 ++++++++++++++++++++++++++++++++++++-----------
block/ll_rw_blk.c | 12 ++++++++--
include/linux/blkdev.h | 9 +++++++
include/linux/elevator.h | 1
4 files changed, 63 insertions(+), 15 deletions(-)
Index: linux-2.6/block/ll_rw_blk.c
===================================================================
--- linux-2.6.orig/block/ll_rw_blk.c
+++ linux-2.6/block/ll_rw_blk.c
@@ -1899,6 +1899,14 @@ EXPORT_SYMBOL(blk_init_queue);
request_queue_t *
blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
{
+ return blk_init_queue_node_elv(rfn, lock, node_id, NULL);
+}
+EXPORT_SYMBOL(blk_init_queue_node);
+
+request_queue_t *
+blk_init_queue_node_elv(request_fn_proc *rfn, spinlock_t *lock, int node_id,
+ char *elv_name)
+{
request_queue_t *q = blk_alloc_queue_node(GFP_KERNEL, node_id);

if (!q)
@@ -1939,7 +1947,7 @@ blk_init_queue_node(request_fn_proc *rfn
/*
* all done
*/
- if (!elevator_init(q, NULL)) {
+ if (!elevator_init(q, elv_name)) {
blk_queue_congestion_threshold(q);
return q;
}
@@ -1947,7 +1955,7 @@ blk_init_queue_node(request_fn_proc *rfn
blk_put_queue(q);
return NULL;
}
-EXPORT_SYMBOL(blk_init_queue_node);
+EXPORT_SYMBOL(blk_init_queue_node_elv);

int blk_get_queue(request_queue_t *q)
{
Index: linux-2.6/include/linux/blkdev.h
===================================================================
--- linux-2.6.orig/include/linux/blkdev.h
+++ linux-2.6/include/linux/blkdev.h
@@ -444,6 +444,12 @@ struct request_queue
#define QUEUE_FLAG_REENTER 6 /* Re-entrancy avoidance */
#define QUEUE_FLAG_PLUGGED 7 /* queue is plugged */
#define QUEUE_FLAG_ELVSWITCH 8 /* don't use elevator, just do FIFO */
+#define QUEUE_FLAG_ELVPINNED 9 /* pin the current elevator */
+
+static inline void blk_queue_pin_elevator(struct request_queue *q)
+{
+ set_bit(QUEUE_FLAG_ELVPINNED, &q->queue_flags);
+}

enum {
/*
@@ -696,6 +702,9 @@ static inline void elv_dispatch_add_tail
/*
* Access functions for manipulating queue properties
*/
+extern request_queue_t *blk_init_queue_node_elv(request_fn_proc *rfn,
+ spinlock_t *lock, int node_id,
+ char *elv_name);
extern request_queue_t *blk_init_queue_node(request_fn_proc *rfn,
spinlock_t *lock, int node_id);
extern request_queue_t *blk_init_queue(request_fn_proc *, spinlock_t *);
Index: linux-2.6/block/elevator.c
===================================================================
--- linux-2.6.orig/block/elevator.c
+++ linux-2.6/block/elevator.c
@@ -856,11 +856,33 @@ fail_register:
return 0;
}

+int elv_iosched_switch(request_queue_t *q, const char *elevator_name)
+{
+ struct elevator_type *e;
+
+ if (test_bit(QUEUE_FLAG_ELVPINNED, &q->queue_flags))
+ return -EPERM;
+
+ e = elevator_get(elevator_name);
+ if (!e)
+ return -EINVAL;
+
+ if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
+ elevator_put(e);
+ return -EEXIST;
+ }
+
+ if (!elevator_switch(q, e))
+ return -ENOMEM;
+
+ return 0;
+}
+
ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
{
char elevator_name[ELV_NAME_MAX];
size_t len;
- struct elevator_type *e;
+ int error;

elevator_name[sizeof(elevator_name) - 1] = '\0';
strncpy(elevator_name, name, sizeof(elevator_name) - 1);
@@ -869,20 +891,27 @@ ssize_t elv_iosched_store(request_queue_
if (len && elevator_name[len - 1] == '\n')
elevator_name[len - 1] = '\0';

- e = elevator_get(elevator_name);
- if (!e) {
- printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
- return -EINVAL;
- }
-
- if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
- elevator_put(e);
- return count;
+ error = elv_iosched_switch(q, elevator_name);
+ switch (error) {
+ case -EPERM:
+ printk(KERN_NOTICE
+ "elevator: cannot switch elevator, pinned\n");
+ break;
+
+ case -EINVAL:
+ printk(KERN_ERR "elevator: type %s not found\n",
+ elevator_name);
+ break;
+
+ case -ENOMEM:
+ printk(KERN_ERR "elevator: switch to %s failed\n",
+ elevator_name);
+ default:
+ error = 0;
+ break;
}

- if (!elevator_switch(q, e))
- printk(KERN_ERR "elevator: switch to %s failed\n",elevator_name);
- return count;
+ return error ?: count;
}

ssize_t elv_iosched_show(request_queue_t *q, char *name)
@@ -914,5 +943,6 @@ EXPORT_SYMBOL(__elv_add_request);
EXPORT_SYMBOL(elv_next_request);
EXPORT_SYMBOL(elv_dequeue_request);
EXPORT_SYMBOL(elv_queue_empty);
+EXPORT_SYMBOL(elv_iosched_switch);
EXPORT_SYMBOL(elevator_exit);
EXPORT_SYMBOL(elevator_init);
Index: linux-2.6/include/linux/elevator.h
===================================================================
--- linux-2.6.orig/include/linux/elevator.h
+++ linux-2.6/include/linux/elevator.h
@@ -107,6 +107,7 @@ extern int elv_may_queue(request_queue_t
extern void elv_completed_request(request_queue_t *, struct request *);
extern int elv_set_request(request_queue_t *, struct request *, struct bio *, gfp_t);
extern void elv_put_request(request_queue_t *, struct request *);
+extern int elv_iosched_switch(request_queue_t *, const char *);

/*
* io scheduler registration
--
-
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