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Subject: Re: [PATCH v3] blk-throtl: optimize IOPS throttle for large IO
 scenarios
To:     axboe@kernel.dk
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        cgroups@vger.kernel.org, Tejun Heo <tj@kernel.org>
References: <65869aaad05475797d63b4c3fed4f529febe3c26.1627876014.git.brookxu@tencent.com>
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From:   "brookxu.cn" <brookxu.cn@gmail.com>
Message-ID: <98864178-cf4d-b86e-81e1-70713a0f1d06@gmail.com>
Date:   Sun, 15 Aug 2021 07:53:06 +0800
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Hi Jens:

Should we apply this patch for new and older kernel ?

Thanks.

On 2021/8/10 6:39 AM, Tejun Heo wrote:
> On Mon, Aug 02, 2021 at 11:51:56AM +0800, brookxu wrote:
>> From: Chunguang Xu <brookxu@tencent.com>
>>
>> After patch 54efd50 (block: make generic_make_request handle
>> arbitrarily sized bios), the IO through io-throttle may be larger,
>> and these IOs may be further split into more small IOs. However,
>> IOPS throttle does not seem to be aware of this change, which
>> makes the calculation of IOPS of large IOs incomplete, resulting
>> in disk-side IOPS that does not meet expectations. Maybe we should
>> fix this problem.
>>
>> We can reproduce it by set max_sectors_kb of disk to 128, set
>> blkio.write_iops_throttle to 100, run a dd instance inside blkio
>> and use iostat to watch IOPS:
>>
>> dd if=/dev/zero of=/dev/sdb bs=1M count=1000 oflag=direct
>>
>> As a result, without this change the average IOPS is 1995, with
>> this change the IOPS is 98.
>>
>> v3: Optimize the use of atomic variables.
>> v2: Use atomic variables to solve synchronization problems.
>>
>> Signed-off-by: Chunguang Xu <brookxu@tencent.com>
> Acked-by: Tejun Heo <tj@kernel.org>
>
> Thanks.
>