[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>
diff --git a/drivers/block/elevator.c b/drivers/block/elevator.c
index af2388e..272d939 100644
--- a/drivers/block/elevator.c
+++ b/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 @@
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 @@
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 @@
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 @@
* 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
@@ -686,18 +691,6 @@
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
*/
if (elevator_attach(q, new_e, e))
@@ -707,11 +700,10 @@
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 @@
* 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);
}