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block: recursive merge requests 

In my workload, thread 1 accesses a, a+2, ..., thread 2 accesses a+1,
a+3,.... When the requests are flushed to queue, a and a+1 are merged
to (a, a+1), a+2 and a+3 too to (a+2, a+3), but (a, a+1) and (a+2, a+3)
aren't merged.
With recursive merge below, the workload throughput gets improved 20%
and context switch drops 60%.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Shaohua Li 2011-12-16 14:00:31 +01:00 committed by Jens Axboe
parent 4a0b75c7d0
commit 274193224c
1 changed files with 12 additions and 4 deletions
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16
block/elevator.c
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@ -515,6 +515,7 @@ static bool elv_attempt_insert_merge(struct request_queue *q,
struct request *rq)
{
struct request *__rq;
bool ret;
if (blk_queue_nomerges(q))
return false;
@ -528,14 +529,21 @@ static bool elv_attempt_insert_merge(struct request_queue *q,
if (blk_queue_noxmerges(q))
return false;
ret = false;
/*
* See if our hash lookup can find a potential backmerge.
*/
__rq = elv_rqhash_find(q, blk_rq_pos(rq));
if (__rq && blk_attempt_req_merge(q, __rq, rq))
return true;
while (1) {
__rq = elv_rqhash_find(q, blk_rq_pos(rq));
if (!__rq || !blk_attempt_req_merge(q, __rq, rq))
break;
return false;
/* The merged request could be merged with others, try again */
ret = true;
rq = __rq;
}
return ret;
}
void elv_merged_request(struct request_queue *q, struct request *rq, int type)