* [patch 2/2]block: recursive merge requests
@ 2011-12-16 1:52 Shaohua Li
2011-12-16 12:59 ` Jens Axboe
2011-12-16 19:34 ` Christoph Hellwig
0 siblings, 2 replies; 4+ messages in thread
From: Shaohua Li @ 2011-12-16 1:52 UTC (permalink / raw)
To: Jens Axboe; +Cc: lkml
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>
---
block/elevator.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
Index: linux/block/elevator.c
===================================================================
--- linux.orig/block/elevator.c 2011-12-16 09:08:50.000000000 +0800
+++ linux/block/elevator.c 2011-12-16 09:08:58.000000000 +0800
@@ -521,6 +521,7 @@ static bool elv_attempt_insert_merge(str
struct request *rq)
{
struct request *__rq;
+ bool ret;
if (blk_queue_nomerges(q))
return false;
@@ -534,14 +535,21 @@ static bool elv_attempt_insert_merge(str
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;
+
+ /* The merged request could be merged with others, try again */
+ ret = true;
+ rq = __rq;
+ }
- return false;
+ return ret;
}
void elv_merged_request(struct request_queue *q, struct request *rq, int type)
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [patch 2/2]block: recursive merge requests
2011-12-16 1:52 [patch 2/2]block: recursive merge requests Shaohua Li
@ 2011-12-16 12:59 ` Jens Axboe
2011-12-16 19:34 ` Christoph Hellwig
1 sibling, 0 replies; 4+ messages in thread
From: Jens Axboe @ 2011-12-16 12:59 UTC (permalink / raw)
To: Shaohua Li; +Cc: lkml
On 2011-12-16 02:52, Shaohua Li wrote:
> 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%.
Interesting, I didn't consider that corner case. Hard to argue with the
numbers, this might positively impact apps using posix aio for instance.
Applied to for-3.3/core.
--
Jens Axboe
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [patch 2/2]block: recursive merge requests
2011-12-16 1:52 [patch 2/2]block: recursive merge requests Shaohua Li
2011-12-16 12:59 ` Jens Axboe
@ 2011-12-16 19:34 ` Christoph Hellwig
2011-12-16 20:16 ` Jens Axboe
1 sibling, 1 reply; 4+ messages in thread
From: Christoph Hellwig @ 2011-12-16 19:34 UTC (permalink / raw)
To: Shaohua Li; +Cc: Jens Axboe, lkml
On Fri, Dec 16, 2011 at 09:52:43AM +0800, Shaohua Li wrote:
> With recursive merge below, the workload throughput gets improved 20%
> and context switch drops 60%.
What workload and what filesystem?
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [patch 2/2]block: recursive merge requests
2011-12-16 19:34 ` Christoph Hellwig
@ 2011-12-16 20:16 ` Jens Axboe
0 siblings, 0 replies; 4+ messages in thread
From: Jens Axboe @ 2011-12-16 20:16 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: Shaohua Li, lkml
On 2011-12-16 20:34, Christoph Hellwig wrote:
> On Fri, Dec 16, 2011 at 09:52:43AM +0800, Shaohua Li wrote:
>> With recursive merge below, the workload throughput gets improved 20%
>> and context switch drops 60%.
>
> What workload and what filesystem?
It shouldn't really matter for the quoted case, where you have 2
processes issuing interleaved reads.
--
Jens Axboe
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2011-12-16 20:16 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2011-12-16 1:52 [patch 2/2]block: recursive merge requests Shaohua Li
2011-12-16 12:59 ` Jens Axboe
2011-12-16 19:34 ` Christoph Hellwig
2011-12-16 20:16 ` Jens Axboe
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