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[BLOCK] Reimplement elevator switch

This patch reimplements elevator switch.  This patch assumes generic
dispatch queue patchset is applied.

 * Each request is tagged with REQ_ELVPRIV flag if it has its elevator
   private data set.
 * Requests which doesn't have REQ_ELVPRIV flag set never enter
   iosched.  They are always directly back inserted to dispatch queue.
   Of course, elevator_put_req_fn is called only for requests which
   have its REQ_ELVPRIV set.
 * Request queue maintains the current number of requests which have
   its elevator data set (elevator_set_req_fn called) in
   q->rq->elvpriv.
 * If a request queue has QUEUE_FLAG_BYPASS set, elevator private data
   is not allocated for new requests.

 To switch to another iosched, we set QUEUE_FLAG_BYPASS and wait until
elvpriv goes to zero; then, we attach the new iosched and clears
QUEUE_FLAG_BYPASS.  New implementation is much simpler and main code
paths are less cluttered, IMHO.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jens Axboe <axboe@suse.de>
master
Tejun Heo 16 years ago
committed by Jens Axboe
parent
commit
cb98fc8bb9
  1. 78
      drivers/block/elevator.c
  2. 142
      drivers/block/ll_rw_blk.c
  3. 10
      include/linux/blkdev.h

78
drivers/block/elevator.c

@ -34,6 +34,7 @@
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/delay.h>
#include <asm/uaccess.h>
@ -131,11 +132,7 @@ static int elevator_attach(request_queue_t *q, struct elevator_type *e,
eq->ops = &e->ops;
eq->elevator_type = e;
INIT_LIST_HEAD(&q->queue_head);
q->last_merge = NULL;
q->elevator = eq;
q->end_sector = 0;
q->boundary_rq = NULL;
if (eq->ops->elevator_init_fn)
ret = eq->ops->elevator_init_fn(q, eq);
@ -184,6 +181,12 @@ int elevator_init(request_queue_t *q, char *name)
struct elevator_queue *eq;
int ret = 0;
INIT_LIST_HEAD(&q->queue_head);
q->last_merge = NULL;
q->end_sector = 0;
q->boundary_rq = NULL;
q->max_back_kb = 0;
elevator_setup_default();
if (!name)
@ -336,23 +339,14 @@ void __elv_add_request(request_queue_t *q, struct request *rq, int where,
q->end_sector = rq_end_sector(rq);
q->boundary_rq = rq;
}
}
} else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
where = ELEVATOR_INSERT_BACK;
if (plug)
blk_plug_device(q);
rq->q = q;
if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))) {
/*
* if drain is set, store the request "locally". when the drain
* is finished, the requests will be handed ordered to the io
* scheduler
*/
list_add_tail(&rq->queuelist, &q->drain_list);
return;
}
switch (where) {
case ELEVATOR_INSERT_FRONT:
rq->flags |= REQ_SOFTBARRIER;
@ -659,25 +653,36 @@ EXPORT_SYMBOL_GPL(elv_unregister);
* switch to new_e io scheduler. be careful not to introduce deadlocks -
* we don't free the old io scheduler, before we have allocated what we
* need for the new one. this way we have a chance of going back to the old
* one, if the new one fails init for some reason. we also do an intermediate
* switch to noop to ensure safety with stack-allocated requests, since they
* don't originate from the block layer allocator. noop is safe here, because
* it never needs to touch the elevator itself for completion events. DRAIN
* flags will make sure we don't touch it for additions either.
* one, if the new one fails init for some reason.
*/
static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
{
elevator_t *e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
struct elevator_type *noop_elevator = NULL;
elevator_t *old_elevator;
elevator_t *old_elevator, *e;
/*
* Allocate new elevator
*/
e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
if (!e)
goto error;
/*
* first step, drain requests from the block freelist
* Turn on BYPASS and drain all requests w/ elevator private data
*/
blk_wait_queue_drained(q, 0);
spin_lock_irq(q->queue_lock);
set_bit(QUEUE_FLAG_BYPASS, &q->queue_flags);
while (q->elevator->ops->elevator_dispatch_fn(q, 1))
;
while (q->rq.elvpriv) {
spin_unlock_irq(q->queue_lock);
msleep(100);
spin_lock_irq(q->queue_lock);
}
spin_unlock_irq(q->queue_lock);
/*
* unregister old elevator data
@ -685,18 +690,6 @@ static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
elv_unregister_queue(q);
old_elevator = q->elevator;
/*
* next step, switch to noop since it uses no private rq structures
* and doesn't allocate any memory for anything. then wait for any
* non-fs requests in-flight
*/
noop_elevator = elevator_get("noop");
spin_lock_irq(q->queue_lock);
elevator_attach(q, noop_elevator, e);
spin_unlock_irq(q->queue_lock);
blk_wait_queue_drained(q, 1);
/*
* attach and start new elevator
*/
@ -707,11 +700,10 @@ static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
goto fail_register;
/*
* finally exit old elevator and start queue again
* finally exit old elevator and turn off BYPASS.
*/
elevator_exit(old_elevator);
blk_finish_queue_drain(q);
elevator_put(noop_elevator);
clear_bit(QUEUE_FLAG_BYPASS, &q->queue_flags);
return;
fail_register:
@ -720,13 +712,13 @@ fail_register:
* one again (along with re-adding the sysfs dir)
*/
elevator_exit(e);
e = NULL;
fail:
q->elevator = old_elevator;
elv_register_queue(q);
blk_finish_queue_drain(q);
clear_bit(QUEUE_FLAG_BYPASS, &q->queue_flags);
kfree(e);
error:
if (noop_elevator)
elevator_put(noop_elevator);
elevator_put(new_e);
printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
}

142
drivers/block/ll_rw_blk.c

@ -263,8 +263,6 @@ void blk_queue_make_request(request_queue_t * q, make_request_fn * mfn)
blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);
blk_queue_activity_fn(q, NULL, NULL);
INIT_LIST_HEAD(&q->drain_list);
}
EXPORT_SYMBOL(blk_queue_make_request);
@ -1050,6 +1048,7 @@ static char *rq_flags[] = {
"REQ_STARTED",
"REQ_DONTPREP",
"REQ_QUEUED",
"REQ_ELVPRIV",
"REQ_PC",
"REQ_BLOCK_PC",
"REQ_SENSE",
@ -1640,9 +1639,9 @@ static int blk_init_free_list(request_queue_t *q)
rl->count[READ] = rl->count[WRITE] = 0;
rl->starved[READ] = rl->starved[WRITE] = 0;
rl->elvpriv = 0;
init_waitqueue_head(&rl->wait[READ]);
init_waitqueue_head(&rl->wait[WRITE]);
init_waitqueue_head(&rl->drain);
rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
mempool_free_slab, request_cachep, q->node);
@ -1785,12 +1784,14 @@ EXPORT_SYMBOL(blk_get_queue);
static inline void blk_free_request(request_queue_t *q, struct request *rq)
{
elv_put_request(q, rq);
if (rq->flags & REQ_ELVPRIV)
elv_put_request(q, rq);
mempool_free(rq, q->rq.rq_pool);
}
static inline struct request *
blk_alloc_request(request_queue_t *q, int rw, struct bio *bio, int gfp_mask)
blk_alloc_request(request_queue_t *q, int rw, struct bio *bio,
int priv, int gfp_mask)
{
struct request *rq = mempool_alloc(q->rq.rq_pool, gfp_mask);
@ -1803,11 +1804,15 @@ blk_alloc_request(request_queue_t *q, int rw, struct bio *bio, int gfp_mask)
*/
rq->flags = rw;
if (!elv_set_request(q, rq, bio, gfp_mask))
return rq;
if (priv) {
if (unlikely(elv_set_request(q, rq, bio, gfp_mask))) {
mempool_free(rq, q->rq.rq_pool);
return NULL;
}
rq->flags |= REQ_ELVPRIV;
}
mempool_free(rq, q->rq.rq_pool);
return NULL;
return rq;
}
/*
@ -1863,22 +1868,18 @@ static void __freed_request(request_queue_t *q, int rw)
* A request has just been released. Account for it, update the full and
* congestion status, wake up any waiters. Called under q->queue_lock.
*/
static void freed_request(request_queue_t *q, int rw)
static void freed_request(request_queue_t *q, int rw, int priv)
{
struct request_list *rl = &q->rq;
rl->count[rw]--;
if (priv)
rl->elvpriv--;
__freed_request(q, rw);
if (unlikely(rl->starved[rw ^ 1]))
__freed_request(q, rw ^ 1);
if (!rl->count[READ] && !rl->count[WRITE]) {
smp_mb();
if (unlikely(waitqueue_active(&rl->drain)))
wake_up(&rl->drain);
}
}
#define blkdev_free_rq(list) list_entry((list)->next, struct request, queuelist)
@ -1893,9 +1894,7 @@ static struct request *get_request(request_queue_t *q, int rw, struct bio *bio,
struct request *rq = NULL;
struct request_list *rl = &q->rq;
struct io_context *ioc = current_io_context(GFP_ATOMIC);
if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)))
goto out;
int priv;
if (rl->count[rw]+1 >= q->nr_requests) {
/*
@ -1940,9 +1939,14 @@ get_rq:
rl->starved[rw] = 0;
if (rl->count[rw] >= queue_congestion_on_threshold(q))
set_queue_congested(q, rw);
priv = !test_bit(QUEUE_FLAG_BYPASS, &q->queue_flags);
if (priv)
rl->elvpriv++;
spin_unlock_irq(q->queue_lock);
rq = blk_alloc_request(q, rw, bio, gfp_mask);
rq = blk_alloc_request(q, rw, bio, priv, gfp_mask);
if (!rq) {
/*
* Allocation failed presumably due to memory. Undo anything
@ -1952,7 +1956,7 @@ get_rq:
* wait queue, but this is pretty rare.
*/
spin_lock_irq(q->queue_lock);
freed_request(q, rw);
freed_request(q, rw, priv);
/*
* in the very unlikely event that allocation failed and no
@ -2470,11 +2474,12 @@ static void __blk_put_request(request_queue_t *q, struct request *req)
*/
if (rl) {
int rw = rq_data_dir(req);
int priv = req->flags & REQ_ELVPRIV;
BUG_ON(!list_empty(&req->queuelist));
blk_free_request(q, req);
freed_request(q, rw);
freed_request(q, rw, priv);
}
}
@ -2802,97 +2807,6 @@ static inline void blk_partition_remap(struct bio *bio)
}
}
void blk_finish_queue_drain(request_queue_t *q)
{
struct request_list *rl = &q->rq;
struct request *rq;
int requeued = 0;
spin_lock_irq(q->queue_lock);
clear_bit(QUEUE_FLAG_DRAIN, &q->queue_flags);
while (!list_empty(&q->drain_list)) {
rq = list_entry_rq(q->drain_list.next);
list_del_init(&rq->queuelist);
elv_requeue_request(q, rq);
requeued++;
}
if (requeued)
q->request_fn(q);
spin_unlock_irq(q->queue_lock);
wake_up(&rl->wait[0]);
wake_up(&rl->wait[1]);
wake_up(&rl->drain);
}
static int wait_drain(request_queue_t *q, struct request_list *rl, int dispatch)
{
int wait = rl->count[READ] + rl->count[WRITE];
if (dispatch)
wait += !list_empty(&q->queue_head);
return wait;
}
/*
* We rely on the fact that only requests allocated through blk_alloc_request()
* have io scheduler private data structures associated with them. Any other
* type of request (allocated on stack or through kmalloc()) should not go
* to the io scheduler core, but be attached to the queue head instead.
*/
void blk_wait_queue_drained(request_queue_t *q, int wait_dispatch)
{
struct request_list *rl = &q->rq;
DEFINE_WAIT(wait);
spin_lock_irq(q->queue_lock);
set_bit(QUEUE_FLAG_DRAIN, &q->queue_flags);
while (wait_drain(q, rl, wait_dispatch)) {
prepare_to_wait(&rl->drain, &wait, TASK_UNINTERRUPTIBLE);
if (wait_drain(q, rl, wait_dispatch)) {
__generic_unplug_device(q);
spin_unlock_irq(q->queue_lock);
io_schedule();
spin_lock_irq(q->queue_lock);
}
finish_wait(&rl->drain, &wait);
}
spin_unlock_irq(q->queue_lock);
}
/*
* block waiting for the io scheduler being started again.
*/
static inline void block_wait_queue_running(request_queue_t *q)
{
DEFINE_WAIT(wait);
while (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))) {
struct request_list *rl = &q->rq;
prepare_to_wait_exclusive(&rl->drain, &wait,
TASK_UNINTERRUPTIBLE);
/*
* re-check the condition. avoids using prepare_to_wait()
* in the fast path (queue is running)
*/
if (test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))
io_schedule();
finish_wait(&rl->drain, &wait);
}
}
static void handle_bad_sector(struct bio *bio)
{
char b[BDEVNAME_SIZE];
@ -2988,8 +2902,6 @@ end_io:
if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
goto end_io;
block_wait_queue_running(q);
/*
* If this device has partitions, remap block n
* of partition p to block n+start(p) of the disk.

10
include/linux/blkdev.h

@ -107,9 +107,9 @@ typedef void (rq_end_io_fn)(struct request *);
struct request_list {
int count[2];
int starved[2];
int elvpriv;
mempool_t *rq_pool;
wait_queue_head_t wait[2];
wait_queue_head_t drain;
};
#define BLK_MAX_CDB 16
@ -211,6 +211,7 @@ enum rq_flag_bits {
__REQ_STARTED, /* drive already may have started this one */
__REQ_DONTPREP, /* don't call prep for this one */
__REQ_QUEUED, /* uses queueing */
__REQ_ELVPRIV, /* elevator private data attached */
/*
* for ATA/ATAPI devices
*/
@ -244,6 +245,7 @@ enum rq_flag_bits {
#define REQ_STARTED (1 << __REQ_STARTED)
#define REQ_DONTPREP (1 << __REQ_DONTPREP)
#define REQ_QUEUED (1 << __REQ_QUEUED)
#define REQ_ELVPRIV (1 << __REQ_ELVPRIV)
#define REQ_PC (1 << __REQ_PC)
#define REQ_BLOCK_PC (1 << __REQ_BLOCK_PC)
#define REQ_SENSE (1 << __REQ_SENSE)
@ -413,8 +415,6 @@ struct request_queue
unsigned int sg_reserved_size;
int node;
struct list_head drain_list;
/*
* reserved for flush operations
*/
@ -442,7 +442,7 @@ enum {
#define QUEUE_FLAG_DEAD 5 /* queue being torn down */
#define QUEUE_FLAG_REENTER 6 /* Re-entrancy avoidance */
#define QUEUE_FLAG_PLUGGED 7 /* queue is plugged */
#define QUEUE_FLAG_DRAIN 8 /* draining queue for sched switch */
#define QUEUE_FLAG_BYPASS 8 /* don't use elevator, just do FIFO */
#define QUEUE_FLAG_FLUSH 9 /* doing barrier flush sequence */
#define blk_queue_plugged(q) test_bit(QUEUE_FLAG_PLUGGED, &(q)->queue_flags)
@ -668,8 +668,6 @@ extern void blk_dump_rq_flags(struct request *, char *);
extern void generic_unplug_device(request_queue_t *);
extern void __generic_unplug_device(request_queue_t *);
extern long nr_blockdev_pages(void);
extern void blk_wait_queue_drained(request_queue_t *, int);
extern void blk_finish_queue_drain(request_queue_t *);
int blk_get_queue(request_queue_t *);
request_queue_t *blk_alloc_queue(int gfp_mask);

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