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Sender: Tejun Heo <htejun@gmail.com>
Date:   Mon, 9 Aug 2021 12:39:20 -1000
From:   Tejun Heo <tj@kernel.org>
To:     brookxu <brookxu.cn@gmail.com>
Cc:     axboe@kernel.dk, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org
Subject: Re: [PATCH v3] blk-throtl: optimize IOPS throttle for large IO
 scenarios
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References: <65869aaad05475797d63b4c3fed4f529febe3c26.1627876014.git.brookxu@tencent.com>
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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.

-- 
tejun