linux-kernel - Re: [PATCH v3] blk-throtl: optimize IOPS throttle for large IO scenarios

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Date:   Sat, 14 Aug 2021 19:14:37 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     brookxu <brookxu.cn@...il.com>, tj@...nel.org
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org
Subject: Re: [PATCH v3] blk-throtl: optimize IOPS throttle for large IO
 scenarios

On 8/1/21 9:51 PM, brookxu wrote:
> From: Chunguang Xu <brookxu@...cent.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.

Applied for 5.15, thanks.

> v3: Optimize the use of atomic variables.
> v2: Use atomic variables to solve synchronization problems.

Just a note for the future, changelog stuff goes below the ---
line.

-- 
Jens Axboe