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Message-ID: <201210170900529064320@gmail.com> Date: Wed, 17 Oct 2012 09:00:55 +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 2012-10-16 15:48 Shaohua Li <shli@...nel.org> Wrote: >2012/10/16 Jianpeng Ma <majianpeng@...il.com>: >> 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. >> Hi shaohua, >> I think i missed some messages about blktrace.So make you confused. >> I trace some message using blktrace: >> 8,16 0 6638 2.453619407 2579 Q W 7493144 + 8 [md0_raid5] >> 8,16 0 6639 2.453620460 2579 G W 7493144 + 8 [md0_raid5] >> 8,16 0 6640 2.453639311 2579 Q W 7493120 + 8 [md0_raid5] >> 8,16 0 6641 2.453639842 2579 G W 7493120 + 8 [md0_raid5] >> 8,16 0 6642 2.453647796 2579 Q W 7493128 + 8 [md0_raid5] >> 8,16 0 6643 2.453647940 2579 M W 7493128 + 8 [md0_raid5] >> 8,16 0 6644 2.453658249 2579 Q W 7493136 + 8 [md0_raid5] >> 8,16 0 6645 2.453658393 2579 M W 7493136 + 8 [md0_raid5] >> 8,16 0 6646 2.453665309 2579 Q W 7493152 + 8 [md0_raid5] >> 8,16 0 6647 2.453665504 2579 M W 7493152 + 8 [md0_raid5] >> 8,16 0 6648 2.453672411 2579 Q W 7493160 + 8 [md0_raid5] >> 8,16 0 6649 2.453672606 2579 M W 7493160 + 8 [md0_raid5] >> 8,16 0 6650 2.453679255 2579 Q W 7493168 + 8 [md0_raid5] >> 8,16 0 6651 2.453679441 2579 M W 7493168 + 8 [md0_raid5] >> 8,16 0 6652 2.453685948 2579 Q W 7493176 + 8 [md0_raid5] >> 8,16 0 6653 2.453686149 2579 M W 7493176 + 8 [md0_raid5] >> 8,16 0 6654 2.453693074 2579 Q W 7493184 + 8 [md0_raid5] >> 8,16 0 6655 2.453693254 2579 M W 7493184 + 8 [md0_raid5] >> 8,16 0 6656 2.453704290 2579 Q W 7493192 + 8 [md0_raid5] >> 8,16 0 6657 2.453704482 2579 M W 7493192 + 8 [md0_raid5] >> 8,16 0 6658 2.453715016 2579 Q W 7493200 + 8 [md0_raid5] >> 8,16 0 6659 2.453715247 2579 M W 7493200 + 8 [md0_raid5] >> 8,16 0 6660 2.453721730 2579 Q W 7493208 + 8 [md0_raid5] >> 8,16 0 6661 2.453721974 2579 M W 7493208 + 8 [md0_raid5] >> 8,16 0 6662 2.453728202 2579 Q W 7493216 + 8 [md0_raid5] >> 8,16 0 6663 2.453728436 2579 M W 7493216 + 8 [md0_raid5] >> 8,16 0 6664 2.453734782 2579 Q W 7493224 + 8 [md0_raid5] >> 8,16 0 6665 2.453735019 2579 M W 7493224 + 8 [md0_raid5] >> 8,16 0 6666 2.453741401 2579 Q W 7493232 + 8 [md0_raid5] >> 8,16 0 6667 2.453741632 2579 M W 7493232 + 8 [md0_raid5] >> 8,16 0 6668 2.453748148 2579 Q W 7493240 + 8 [md0_raid5] >> 8,16 0 6669 2.453748386 2579 M W 7493240 + 8 [md0_raid5] >> 8,16 0 6670 2.453851843 2579 I W 7493144 + 104 [md0_raid5] >> 8,16 0 0 2.453853661 0 m N cfq2579 insert_request >> 8,16 0 6671 2.453854064 2579 I W 7493120 + 24 [md0_raid5] >> 8,16 0 0 2.453854439 0 m N cfq2579 insert_request >> 8,16 0 6672 2.453854793 2579 U N [md0_raid5] 2 >> 8,16 0 0 2.453855513 0 m N cfq2579 Not idling. st->count:1 >> 8,16 0 0 2.453855927 0 m N cfq2579 dispatch_insert >> 8,16 0 0 2.453861771 0 m N cfq2579 dispatched a request >> 8,16 0 0 2.453862248 0 m N cfq2579 activate rq, drv=1 >> 8,16 0 6673 2.453862332 2579 D W 7493120 + 24 [md0_raid5] >> 8,16 0 0 2.453865957 0 m N cfq2579 Not idling. st->count:1 >> 8,16 0 0 2.453866269 0 m N cfq2579 dispatch_insert >> 8,16 0 0 2.453866707 0 m N cfq2579 dispatched a request >> 8,16 0 0 2.453867061 0 m N cfq2579 activate rq, drv=2 >> 8,16 0 6674 2.453867145 2579 D W 7493144 + 104 [md0_raid5] >> 8,16 0 6675 2.454147608 0 C W 7493120 + 24 [0] >> 8,16 0 0 2.454149357 0 m N cfq2579 complete rqnoidle 0 >> 8,16 0 6676 2.454791505 0 C W 7493144 + 104 [0] >> 8,16 0 0 2.454794803 0 m N cfq2579 complete rqnoidle 0 >> 8,16 0 0 2.454795160 0 m N cfq schedule dispatch >> >> From above messages,we can found why rq[W 7493144 + 104] and rq[W 7493120 + 24] do not merge. >> Because the bio order is: >> 8,16 0 6638 2.453619407 2579 Q W 7493144 + 8 [md0_raid5] >> 8,16 0 6639 2.453620460 2579 G W 7493144 + 8 [md0_raid5] >> 8,16 0 6640 2.453639311 2579 Q W 7493120 + 8 [md0_raid5] >> 8,16 0 6641 2.453639842 2579 G W 7493120 + 8 [md0_raid5] >> Because the bio(7493144) first and bio(7493120) later.So the subsequent bios will be divided into two parts. >> As you mentions, recursive merge doesn't work for this situation. >> Why is can occur?I think because the raid operation.It disorder some bios. >> >> Is it ok? If ok,i'll resend the patch using useful message. > >So the real problem is attempt_plug_merge can't do recursive merge >for merged request, because there is no elevator info attached to the >request, so we can only do the merge in elv_attempt_insert_merge(). > >I'm still hoping elv_attempt_insert_merge() can do frontmerge and >recursive merge, which is more generic and can solve more >problems than your patch. But giving the simplicity of your patch, >maybe we should merge yours at that time. Thanks your time! I'll resend it.
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