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block: elevator quiescing helpers

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Simple helper functions to quiesce the request queue. These are
currently only used for switching IO schedulers on-the-fly, but
we can use them to properly switch IO accounting on and off as well.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2009-03-27 10:30:47 +01:00
parent d508afb437
commit 6c7e8cee6a
2 changed files with 31 additions and 13 deletions
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4
block/blk.h
View file

@ -70,6 +70,10 @@ void blk_queue_congestion_threshold(struct request_queue *q);
int blk_dev_init(void);
void elv_quisce_start(struct request_queue *q);
void elv_quisce_end(struct request_queue *q);
/*
* Return the threshold (number of used requests) at which the queue is
* considered to be congested. It include a little hysteresis to keep the

40
block/elevator.c
View file

@ -587,6 +587,31 @@ static void elv_drain_elevator(struct request_queue *q)
}
}
/*
* Call with queue lock held, interrupts disabled
*/
void elv_quisce_start(struct request_queue *q)
{
queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
/*
* make sure we don't have any requests in flight
*/
elv_drain_elevator(q);
while (q->rq.elvpriv) {
blk_start_queueing(q);
spin_unlock_irq(q->queue_lock);
msleep(10);
spin_lock_irq(q->queue_lock);
elv_drain_elevator(q);
}
}
void elv_quisce_end(struct request_queue *q)
{
queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
}
void elv_insert(struct request_queue *q, struct request *rq, int where)
{
struct list_head *pos;
@ -1101,18 +1126,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
* Turn on BYPASS and drain all requests w/ elevator private data
*/
spin_lock_irq(q->queue_lock);
queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
elv_drain_elevator(q);
while (q->rq.elvpriv) {
blk_start_queueing(q);
spin_unlock_irq(q->queue_lock);
msleep(10);
spin_lock_irq(q->queue_lock);
elv_drain_elevator(q);
}
elv_quisce_start(q);
/*
* Remember old elevator.
@ -1136,7 +1150,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
*/
elevator_exit(old_elevator);
spin_lock_irq(q->queue_lock);
queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
elv_quisce_end(q);
spin_unlock_irq(q->queue_lock);
blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);