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Subject: Re: [PATCH] md/raid10: Only check QUEUE_FLAG_IO_STAT when issuing io
To:     linan666@huaweicloud.com, song@kernel.org, jgq516@gmail.com
Cc:     linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        linan122@huawei.com, yi.zhang@huawei.com, houtao1@huawei.com,
        yangerkun@huawei.com, "yukuai (C)" <yukuai3@huawei.com>
References: <20230609094320.2397604-1-linan666@huaweicloud.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <8d2134a6-90dc-822b-52ef-cd7cc8060b36@huaweicloud.com>
Date:   Sat, 10 Jun 2023 10:32:50 +0800
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Hi,

?? 2023/06/09 17:43, linan666@huaweicloud.com д??:
> From: Li Nan <linan122@huawei.com>
> 
> /sys/block/[device]/queue/iostats is used to control whether to count io
> stat. Write 0 to it will clear queue_flags QUEUE_FLAG_IO_STAT which means
> iostats is disabled. If we disable iostats and later endable it, the io
> issued during this period will be counted incorrectly, inflight will be
> decreased to -1.
> 
>    //T1 set iostats
>    echo 0 > /sys/block/md0/queue/iostats
>     clear QUEUE_FLAG_IO_STAT
> 
> 			//T2 issue io
> 			if (QUEUE_FLAG_IO_STAT) -> false
> 			 bio_start_io_acct
> 			  inflight++
> 
>    echo 1 > /sys/block/md0/queue/iostats
>     set QUEUE_FLAG_IO_STAT
> 
> 					//T3 io end
> 					if (QUEUE_FLAG_IO_STAT) -> true
> 					 bio_end_io_acct
> 					  inflight--	-> -1
> 
> Also, if iostats is enabled while issuing io but disabled while io end,
> inflight will never be decreased.
> 
> Fix it by checking start_time when io end. Only check QUEUE_FLAG_IO_STAT
> while issuing io, just like request based devices.
> 
> Fixes: 528bc2cf2fcc ("md/raid10: enable io accounting")
> Signed-off-by: Li Nan <linan122@huawei.com>
> ---
>   drivers/md/raid10.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 381c21f7fb06..bf9dca5c25c3 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -325,7 +325,7 @@ static void raid_end_bio_io(struct r10bio *r10_bio)
>   	if (!test_bit(R10BIO_Uptodate, &r10_bio->state))
>   		bio->bi_status = BLK_STS_IOERR;
>   
> -	if (blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
> +	if (r10_bio->start_time)
>   		bio_end_io_acct(bio, r10_bio->start_time);

This patch LGTM, can you change this for raid1 as well? raid0 and
raid456 is using md_account_bio(), and they don't have such problem.

Thanks,
Kuai
>   	bio_endio(bio);
>   	/*
>