linux-kernel - Re: [PATCH -next v5 0/3] support concurrent sync io for bfq on a specail occasion

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Date:   Sat, 21 May 2022 15:22:34 +0800
From:   "yukuai (C)" <yukuai3@...wei.com>
To:     <paolo.valente@...aro.org>, <axboe@...nel.dk>
CC:     <jack@...e.cz>, <tj@...nel.org>, <linux-block@...r.kernel.org>,
        <cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <yi.zhang@...wei.com>
Subject: Re: [PATCH -next v5 0/3] support concurrent sync io for bfq on a
 specail occasion

在 2022/05/14 17:29, yukuai (C) 写道:
> 在 2022/05/05 9:00, yukuai (C) 写道:
>> Hi, Paolo
>>
>> Can you take a look at this patchset? It has been quite a long time
>> since we spotted this problem...
>>
> 
> friendly ping ...
friendly ping ...
>> Thanks,
>> Kuai
>>
>> 在 2022/04/28 20:08, Yu Kuai 写道:
>>> Changes in v5:
>>>   - rename bfq_add_busy_queues() to bfq_inc_busy_queues() in patch 1
>>>   - fix wrong definition in patch 1
>>>   - fix spelling mistake in patch 2: leaset -> least
>>>   - update comments in patch 3
>>>   - add reviewed-by tag in patch 2,3
>>>
>>> Changes in v4:
>>>   - split bfq_update_busy_queues() to bfq_add/dec_busy_queues(),
>>>     suggested by Jan Kara.
>>>   - remove unused 'in_groups_with_pending_reqs',
>>>
>>> Changes in v3:
>>>   - remove the cleanup patch that is irrelevant now(I'll post it
>>>     separately).
>>>   - instead of hacking wr queues and using weights tree 
>>> insertion/removal,
>>>     using bfq_add/del_bfqq_busy() to count the number of groups
>>>     (suggested by Jan Kara).
>>>
>>> Changes in v2:
>>>   - Use a different approch to count root group, which is much simple.
>>>
>>> Currently, bfq can't handle sync io concurrently as long as they
>>> are not issued from root group. This is because
>>> 'bfqd->num_groups_with_pending_reqs > 0' is always true in
>>> bfq_asymmetric_scenario().
>>>
>>> The way that bfqg is counted into 'num_groups_with_pending_reqs':
>>>
>>> Before this patchset:
>>>   1) root group will never be counted.
>>>   2) Count if bfqg or it's child bfqgs have pending requests.
>>>   3) Don't count if bfqg and it's child bfqgs complete all the requests.
>>>
>>> After this patchset:
>>>   1) root group is counted.
>>>   2) Count if bfqg have at least one bfqq that is marked busy.
>>>   3) Don't count if bfqg doesn't have any busy bfqqs.
>>>
>>> The main reason to use busy state of bfqq instead of 'pending requests'
>>> is that bfqq can stay busy after dispatching the last request if idling
>>> is needed for service guarantees.
>>>
>>> With the above changes, concurrent sync io can be supported if only
>>> one group is activated.
>>>
>>> fio test script(startdelay is used to avoid queue merging):
>>> [global]
>>> filename=/dev/nvme0n1
>>> allow_mounted_write=0
>>> ioengine=psync
>>> direct=1
>>> ioscheduler=bfq
>>> offset_increment=10g
>>> group_reporting
>>> rw=randwrite
>>> bs=4k
>>>
>>> [test1]
>>> numjobs=1
>>>
>>> [test2]
>>> startdelay=1
>>> numjobs=1
>>>
>>> [test3]
>>> startdelay=2
>>> numjobs=1
>>>
>>> [test4]
>>> startdelay=3
>>> numjobs=1
>>>
>>> [test5]
>>> startdelay=4
>>> numjobs=1
>>>
>>> [test6]
>>> startdelay=5
>>> numjobs=1
>>>
>>> [test7]
>>> startdelay=6
>>> numjobs=1
>>>
>>> [test8]
>>> startdelay=7
>>> numjobs=1
>>>
>>> test result:
>>> running fio on root cgroup
>>> v5.18-rc1:       550 Mib/s
>>> v5.18-rc1-patched: 550 Mib/s
>>>
>>> running fio on non-root cgroup
>>> v5.18-rc1:       349 Mib/s
>>> v5.18-rc1-patched: 550 Mib/s
>>>
>>> Note that I also test null_blk with "irqmode=2
>>> completion_nsec=100000000(100ms) hw_queue_depth=1", and tests show
>>> that service guarantees are still preserved.
>>>
>>> Previous versions:
>>> RFC: 
>>> https://lore.kernel.org/all/20211127101132.486806-1-yukuai3@huawei.com/
>>> v1: 
>>> https://lore.kernel.org/all/20220305091205.4188398-1-yukuai3@huawei.com/
>>> v2: 
>>> https://lore.kernel.org/all/20220416093753.3054696-1-yukuai3@huawei.com/
>>> v3: 
>>> https://lore.kernel.org/all/20220427124722.48465-1-yukuai3@huawei.com/
>>> v4: 
>>> https://lore.kernel.org/all/20220428111907.3635820-1-yukuai3@huawei.com/
>>>
>>> Yu Kuai (3):
>>>    block, bfq: record how many queues are busy in bfq_group
>>>    block, bfq: refactor the counting of 'num_groups_with_pending_reqs'
>>>    block, bfq: do not idle if only one group is activated
>>>
>>>   block/bfq-cgroup.c  |  1 +
>>>   block/bfq-iosched.c | 48 +++-----------------------------------
>>>   block/bfq-iosched.h | 57 +++++++--------------------------------------
>>>   block/bfq-wf2q.c    | 35 +++++++++++++++++-----------
>>>   4 files changed, 35 insertions(+), 106 deletions(-)
>>>