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Message-ID: <201210161040097340482@gmail.com> Date: Tue, 16 Oct 2012 10:40:14 +0800 From: "Jianpeng Ma" <majianpeng@...il.com> To: shli <shli@...nel.org> Cc: axboe <axboe@...nel.dk>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: Re: [PATCH] block: Add blk_rq_pos(rq) to sort rq when plushing plug-list. On 2012-10-15 21:18 Shaohua Li <shli@...nel.org> Wrote: >2012/10/15 Shaohua Li <shli@...ionio.com>: >> 2012/10/15 Jianpeng Ma <majianpeng@...il.com>: >>> My workload is a raid5 which had 16 disks. And used our filesystem to >>> write using direct-io mode. >>> I used the blktrace to find those message: >>> >>> 8,16 0 3570 1.083923979 2519 I W 144323176 + 24 [md127_raid5] >>> 8,16 0 0 1.083926214 0 m N cfq2519 insert_request >>> 8,16 0 3571 1.083926586 2519 I W 144323072 + 104 [md127_raid5] >>> 8,16 0 0 1.083926952 0 m N cfq2519 insert_request >>> 8,16 0 3572 1.083927180 2519 U N [md127_raid5] 2 >>> 8,16 0 0 1.083927870 0 m N cfq2519 Not idling.st->count:1 >>> 8,16 0 0 1.083928320 0 m N cfq2519 dispatch_insert >>> 8,16 0 0 1.083928951 0 m N cfq2519 dispatched a request >>> 8,16 0 0 1.083929443 0 m N cfq2519 activate rq,drv=1 >>> 8,16 0 3573 1.083929530 2519 D W 144323176 + 24 [md127_raid5] >>> 8,16 0 0 1.083933883 0 m N cfq2519 Not idling.st->count:1 >>> 8,16 0 0 1.083934189 0 m N cfq2519 dispatch_insert >>> 8,16 0 0 1.083934654 0 m N cfq2519 dispatched a request >>> 8,16 0 0 1.083935014 0 m N cfq2519 activate rq,drv=2 >>> 8,16 0 3574 1.083935101 2519 D W 144323072 + 104 [md127_raid5] >>> 8,16 0 3575 1.084196179 0 C W 144323176 + 24 [0] >>> 8,16 0 0 1.084197979 0 m N cfq2519 complete rqnoidle 0 >>> 8,16 0 3576 1.084769073 0 C W 144323072 + 104 [0] >>> ...... >>> 8,16 1 3596 1.091394357 2519 I W 144322544 + 16 [md127_raid5] >>> 8,16 1 0 1.091396181 0 m N cfq2519 insert_request >>> 8,16 1 3597 1.091396571 2519 I W 144322520 + 24 [md127_raid5] >>> 8,16 1 0 1.091396934 0 m N cfq2519 insert_request >>> 8,16 1 3598 1.091397165 2519 I W 144322488 + 32 [md127_raid5] >>> 8,16 1 0 1.091397477 0 m N cfq2519 insert_request >>> 8,16 1 3599 1.091397708 2519 I W 144322432 + 56 [md127_raid5] >>> 8,16 1 0 1.091398023 0 m N cfq2519 insert_request >>> 8,16 1 3600 1.091398284 2519 U N [md127_raid5] 4 >>> 8,16 1 0 1.091398986 0 m N cfq2519 Not idling. st->count:1 >>> 8,16 1 0 1.091399511 0 m N cfq2519 dispatch_insert >>> 8,16 1 0 1.091400217 0 m N cfq2519 dispatched a request >>> 8,16 1 0 1.091400688 0 m N cfq2519 activate rq,drv=1 >>> 8,16 1 3601 1.091400766 2519 D W 144322544 + 16 [md127_raid5] >>> 8,16 1 0 1.091406151 0 m N cfq2519 Not idling.st->count:1 >>> 8,16 1 0 1.091406460 0 m N cfq2519 dispatch_insert >>> 8,16 1 0 1.091406931 0 m N cfq2519 dispatched a request >>> 8,16 1 0 1.091407291 0 m N cfq2519 activate rq,drv=2 >>> 8,16 1 3602 1.091407378 2519 D W 144322520 + 24 [md127_raid5] >>> 8,16 1 0 1.091414006 0 m N cfq2519 Not idling.st->count:1 >>> 8,16 1 0 1.091414297 0 m N cfq2519 dispatch_insert >>> 8,16 1 0 1.091414702 0 m N cfq2519 dispatched a request >>> 8,16 1 0 1.091415047 0 m N cfq2519 activate rq, drv=3 >>> 8,16 1 3603 1.091415125 2519 D W 144322488 + 32 [md127_raid5] >>> 8,16 1 0 1.091416469 0 m N cfq2519 Not idling.st->count:1 >>> 8,16 1 0 1.091416754 0 m N cfq2519 dispatch_insert >>> 8,16 1 0 1.091417186 0 m N cfq2519 dispatched a request >>> 8,16 1 0 1.091417535 0 m N cfq2519 activate rq,drv=4 >>> 8,16 1 3604 1.091417628 2519 D W 144322432 + 56 [md127_raid5] >>> 8,16 1 3605 1.091857225 4393 C W 144322544 + 16 [0] >>> 8,16 1 0 1.091858753 0 m N cfq2519 complete rqnoidle 0 >>> 8,16 1 3606 1.092068456 4393 C W 144322520 + 24 [0] >>> 8,16 1 0 1.092069851 0 m N cfq2519 complete rqnoidle 0 >>> 8,16 1 3607 1.092350440 4393 C W 144322488 + 32 [0] >>> 8,16 1 0 1.092351688 0 m N cfq2519 complete rqnoidle 0 >>> 8,16 1 3608 1.093629323 0 C W 144322432 + 56 [0] >>> 8,16 1 0 1.093631151 0 m N cfq2519 complete rqnoidle 0 >>> 8,16 1 0 1.093631574 0 m N cfq2519 will busy wait >>> 8,16 1 0 1.093631829 0 m N cfq schedule dispatch >>> >>> Because in func "elv_attempt_insert_merge", it only to try to >>> backmerge.So the four request can't merge in theory. >>> I trace ten minutes and count those situation, it can count 25%. >>> >>> With the patch,i tested and not found situation like above. >>> >>> Signed-off-by: Jianpeng Ma <majianpeng@...il.com> >>> --- >>> block/blk-core.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/block/blk-core.c b/block/blk-core.c >>> index a33870b..3c95c4d 100644 >>> --- a/block/blk-core.c >>> +++ b/block/blk-core.c >>> @@ -2868,7 +2868,8 @@ static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b) >>> struct request *rqa = container_of(a, struct request, queuelist); >>> struct request *rqb = container_of(b, struct request, queuelist); >>> >>> - return !(rqa->q <= rqb->q); >>> + return !(rqa->q < rqb->q || >>> + (rqa->q == rqb->q && blk_rq_pos(rqa) < blk_rq_pos(rqb))); >>> } >> >> Does this one help too? >> http://marc.info/?l=linux-kernel&m=132399972114668&w=2 >> >> I thought the real problem is we don't do recursive request >> merge. I had no objection to the patch itself, but just hope we >> can make recursive merge work, which is more generic. > >Oh, wait, the 4 requests aren't merged completely in your case. >And the requests are from one thread and plug context. >Not the issue I mentioned. I'm wondering how this could happen. >they should be merged in attempt_plug_merge already. Yes, i ignore this. The real problem is why not merge in attempt_plug_mege? I'll do further study. Thanks! Jianpeng
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