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Subject: Re: [PATCH -next v2 0/5] support concurrent sync io for bfq on a
 specail occasion
To:     <jack@suse.cz>, <paolo.valente@linaro.org>, <axboe@kernel.dk>,
        <tj@kernel.org>
CC:     <linux-block@vger.kernel.org>, <cgroups@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <yi.zhang@huawei.com>
References: <20220416093753.3054696-1-yukuai3@huawei.com>
From:   "yukuai (C)" <yukuai3@huawei.com>
Message-ID: <c120ed31-860d-99d2-5c97-4023766fea96@huawei.com>
Date:   Sun, 24 Apr 2022 10:44:28 +0800
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friendly ping ...

?? 2022/04/16 17:37, Yu Kuai д??:
> Changes in v2:
>   - Use a different aporch 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 to '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 pending requests.
> 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.
> 
>   3) Don't count if bfqg complete all the requests.
> 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
> v5.18-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
> 
> Yu Kuai (5):
>    block, bfq: cleanup bfq_weights_tree add/remove apis
>    block, bfq: add fake weight_counter for weight-raised queue
>    bfq, block: record how many queues have pending requests in bfq_group
>    block, bfq: refactor the counting of 'num_groups_with_pending_reqs'
>    block, bfq: do not idle if only one cgroup is activated
> 
>   block/bfq-cgroup.c  |  1 +
>   block/bfq-iosched.c | 90 +++++++++++++++++++--------------------------
>   block/bfq-iosched.h | 26 ++++++-------
>   block/bfq-wf2q.c    | 30 +++------------
>   4 files changed, 56 insertions(+), 91 deletions(-)
>