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Subject: Re: [PATCH -next 00/11] support concurrent sync io for bfq on a
 specail occasion
From:   "yukuai (C)" <yukuai3@huawei.com>
To:     <tj@kernel.org>, <axboe@kernel.dk>, <paolo.valente@linaro.org>,
        <jack@suse.cz>
CC:     <cgroups@vger.kernel.org>, <linux-block@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <yi.zhang@huawei.com>
References: <20220305091205.4188398-1-yukuai3@huawei.com>
 <e299180e-cdbd-0837-8478-5e397ac8166b@huawei.com>
 <11fda851-a552-97ea-d083-d0288c17ba53@huawei.com>
Message-ID: <e78fc7c5-cf08-9fc7-3f81-7ff8aaf37673@huawei.com>
Date:   Fri, 25 Mar 2022 15:30:26 +0800
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friendly ping ...

在 2022/03/17 9:49, yukuai (C) 写道:
> friendly ping ...
> 
> 在 2022/03/11 14:31, yukuai (C) 写道:
>> friendly ping ...
>>
>> 在 2022/03/05 17:11, Yu Kuai 写道:
>>> 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().
>>>
>>> This patchset tries to support concurrent sync io if all the sync ios
>>> are issued from the same cgroup:
>>>
>>> 1) Count root_group into 'num_groups_with_pending_reqs', patch 1-5;
>>>
>>> 2) Don't idle if 'num_groups_with_pending_reqs' is 1, patch 6;
>>>
>>> 3) Don't count the group if the group doesn't have pending requests,
>>> while it's child groups may have pending requests, patch 7;
>>>
>>> This is because, for example:
>>> if sync ios are issued from cgroup /root/c1/c2, root, c1 and c2
>>> will all be counted into 'num_groups_with_pending_reqs',
>>> which makes it impossible to handle sync ios concurrently.
>>>
>>> 4) Decrease 'num_groups_with_pending_reqs' when the last queue completes
>>> all the requests, while child groups may still have pending
>>> requests, patch 8-10;
>>>
>>> This is because, for example:
>>> t1 issue sync io on root group, t2 and t3 issue sync io on the same
>>> child group. num_groups_with_pending_reqs is 2 now.
>>> After t1 stopped, num_groups_with_pending_reqs is still 2. sync io from
>>> t2 and t3 still can't be handled concurrently.
>>>
>>> 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
>>> v5.17-rc6:       550 Mib/s
>>> v5.17-rc6-patched: 550 Mib/s
>>>
>>> running fio on non-root cgroup
>>> v5.17-rc6:       349 Mib/s
>>> v5.17-rc6-patched: 550 Mib/s
>>>
>>> Yu Kuai (11):
>>>    block, bfq: add new apis to iterate bfq entities
>>>    block, bfq: apply news apis where root group is not expected
>>>    block, bfq: cleanup for __bfq_activate_requeue_entity()
>>>    block, bfq: move the increasement of 
>>> 'num_groups_with_pending_reqs' to
>>>      it's caller
>>>    block, bfq: count root group into 'num_groups_with_pending_reqs'
>>>    block, bfq: do not idle if only one cgroup is activated
>>>    block, bfq: only count parent bfqg when bfqq is activated
>>>    block, bfq: record how many queues have pending requests in bfq_group
>>>    block, bfq: move forward __bfq_weights_tree_remove()
>>>    block, bfq: decrease 'num_groups_with_pending_reqs' earlier
>>>    block, bfq: cleanup bfqq_group()
>>>
>>>   block/bfq-cgroup.c  | 13 +++----
>>>   block/bfq-iosched.c | 87 +++++++++++++++++++++++----------------------
>>>   block/bfq-iosched.h | 41 +++++++++++++--------
>>>   block/bfq-wf2q.c    | 56 +++++++++++++++--------------
>>>   4 files changed, 106 insertions(+), 91 deletions(-)
>>>