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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>
Message-ID: <11fda851-a552-97ea-d083-d0288c17ba53@huawei.com>
Date:   Thu, 17 Mar 2022 09:49:16 +0800
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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(-)
>>