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[BLOCK] Reimplement elevator switch

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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>
This commit is contained in:
Tejun Heo
2005-10-28 08:29:39 +02:00
committed by Jens Axboe
parent cb19833dcc
commit cb98fc8bb9
3 changed files with 66 additions and 164 deletions
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10
include/linux/blkdev.h
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@@ -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);