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SubjectRe: [PATCH] block: kyber: make kyber more friendly with merging
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On 5/22/18 10:17 AM, Holger Hoffstätte wrote:
> On 05/22/18 16:48, Jianchao Wang wrote:
>> Currently, kyber is very unfriendly with merging. kyber depends
>> on ctx rq_list to do merging, however, most of time, it will not
>> leave any requests in ctx rq_list. This is because even if tokens
>> of one domain is used up, kyber will try to dispatch requests
>> from other domain and flush the rq_list there.
>>
>> To improve this, we setup kyber_ctx_queue (kcq) which is similar
>> with ctx, but it has rq_lists for different domain and build same
>> mapping between kcq and khd as the ctx & hctx. Then we could merge,
>> insert and dispatch for different domains separately. If one domain
>> token is used up, the requests could be left in the rq_list of
>> that domain and maybe merged with following io.
>>
>> Following is my test result on machine with 8 cores and NVMe card
>> INTEL SSDPEKKR128G7
>>
>> fio size=256m ioengine=libaio iodepth=64 direct=1 numjobs=8
>> seq/random
>> +------+---------------------------------------------------------------+
>> |patch?| bw(MB/s) | iops | slat(usec) | clat(usec) | merge |
>> +----------------------------------------------------------------------+
>> | w/o | 606/612 | 151k/153k | 6.89/7.03 | 3349.21/3305.40 | 0/0 |
>> +----------------------------------------------------------------------+
>> | w/ | 1083/616 | 277k/154k | 4.93/6.95 | 1830.62/3279.95 | 223k/3k |
>> +----------------------------------------------------------------------+
>> When set numjobs to 16, the bw and iops could reach 1662MB/s and 425k
>> on my platform.
>>
>> Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
>
> <snip>
>
> This looks great but prevents kyber from being built as module,
> which is AFAIK supposed to work (and works now):
>
> ..
> CC [M] block/kyber-iosched.o
> Building modules, stage 2.
> MODPOST 313 modules
> ERROR: "bio_attempt_back_merge" [block/kyber-iosched.ko] undefined!
> ERROR: "bio_attempt_front_merge" [block/kyber-iosched.ko] undefined!
> ERROR: "bio_attempt_discard_merge" [block/kyber-iosched.ko] undefined!
> ERROR: "blk_try_merge" [block/kyber-iosched.ko] undefined!
> ERROR: "blk_rq_merge_ok" [block/kyber-iosched.ko] undefined!
> ..
>
> It does build fine when compiled in, obviously. :)

It's basically duplicating the contents of blk_attempt_plug_merge().
I would suggest abstracting out the list loop and merge check
into a helper, that could then both be called from kyber and the
plug merge function.

--
Jens Axboe

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