Hi,
Going over this a bit, an deviant from the original design of
elevator_linus seems to have snuck in. Well, almost, I've been aware of
this for some time...
The idea was _not_ to account request merges, since they will (in by far
the most cases) incur the cost of a seek. Instead we just account seeks,
any seek (and please don't start a debate on short vs long seeks again,
I'm not listening). The attached patch corrects this, and also corrects
the initial sequence numbers (typically this would be sequence / 8
number of seeks allowed to pass a request now).
I'll do some formal timing on this later.
--
Jens Axboe
--- drivers/block/ll_rw_blk.c~ Tue May 29 17:53:58 2001
+++ drivers/block/ll_rw_blk.c Tue May 29 17:54:38 2001
@@ -742,7 +742,6 @@
case ELEVATOR_BACK_MERGE:
if (!q->back_merge_fn(q, req, bh, max_segments))
break;
- elevator->elevator_merge_cleanup_fn(q, req, count);
req->bhtail->b_reqnext = bh;
req->bhtail = bh;
req->nr_sectors = req->hard_nr_sectors += count;
@@ -754,7 +753,6 @@
case ELEVATOR_FRONT_MERGE:
if (!q->front_merge_fn(q, req, bh, max_segments))
break;
- elevator->elevator_merge_cleanup_fn(q, req, count);
bh->b_reqnext = req->bh;
req->bh = bh;
req->buffer = bh->b_data;
@@ -775,8 +773,10 @@
* request. if no hints, just add it to the back
* of the queue
*/
- if (req)
+ if (req) {
insert_here = &req->queue;
+ elevator->elevator_merge_cleanup_fn(q, req, count);
+ }
break;
default:
--- drivers/block/elevator.c~ Tue May 29 17:54:03 2001
+++ drivers/block/elevator.c Tue May 29 17:59:28 2001
@@ -110,7 +110,6 @@
break;
} else if (__rq->sector - count == bh->b_rsector) {
ret = ELEVATOR_FRONT_MERGE;
- __rq->elevator_sequence -= count;
*req = __rq;
break;
}
@@ -126,10 +125,10 @@
/*
* second pass scan of requests that got passed over, if any
*/
- while ((entry = entry->next) != head) {
+ do {
struct request *tmp = blkdev_entry_to_request(entry);
tmp->elevator_sequence -= count;
- }
+ } while ((entry = entry->next) != head);
}
void elevator_linus_merge_req(struct request *req, struct request *next)
--- include/linux/elevator.h~ Tue May 29 17:54:10 2001
+++ include/linux/elevator.h Tue May 29 17:55:25 2001
@@ -93,8 +93,8 @@
#define ELEVATOR_LINUS \
((elevator_t) { \
- 8192, /* read passovers */ \
- 16384, /* write passovers */ \
+ 1024, /* read passovers */ \
+ 4096, /* write passovers */ \
\
elevator_linus_merge, /* elevator_merge_fn */ \
elevator_linus_merge_cleanup, /* elevator_merge_cleanup_fn */ \
