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From:   Song Liu <song@kernel.org>
Date:   Thu, 15 Jun 2023 23:12:28 -0700
Message-ID: <CAPhsuW6imRp9jseup660xQiV7optVwk-vPWz77aG3=4niUrMRQ@mail.gmail.com>
Subject: Re: [PATCH] md/raid10: Only check QUEUE_FLAG_IO_STAT when issuing io
To:     linan666@huaweicloud.com
Cc:     jgq516@gmail.com, linux-raid@vger.kernel.org,
        linux-kernel@vger.kernel.org, linan122@huawei.com,
        yukuai3@huawei.com, yi.zhang@huawei.com, houtao1@huawei.com,
        yangerkun@huawei.com
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On Fri, Jun 9, 2023 at 2:47=E2=80=AFAM <linan666@huaweicloud.com> wrote:
>
> 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>

The subject and commit log is a little confusing. I updated it a little
bit and applied to md-next.

Thanks,
Song


> ---
>  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 =3D 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);
>         bio_endio(bio);
>         /*
> --
> 2.39.2
>