From cb98fc8bb9c141009e2bda99c0db39d387e142cf Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 28 Oct 2005 08:29:39 +0200 Subject: [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 Signed-off-by: Jens Axboe --- drivers/block/elevator.c | 78 ++++++++++++++++++++++-------------------------- 1 file changed, 35 insertions(+), 43 deletions(-) (limited to 'drivers/block/elevator.c') diff --git a/drivers/block/elevator.c b/drivers/block/elevator.c index af2388e73f61..272d93946621 100644 --- a/drivers/block/elevator.c +++ b/drivers/block/elevator.c @@ -34,6 +34,7 @@ #include #include #include +#include #include @@ -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); } -- cgit v1.2.2