linux-kernel - Re: [PATCH v2 2/2] md: don't account sync_io if iostats of the disk is disabled

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Date: Fri, 15 Dec 2023 01:08:06 -0800
From: Song Liu <song@...nel.org>
To: linan666@...weicloud.com
Cc: axboe@...nel.dk, linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-block@...r.kernel.org, yukuai3@...wei.com, yi.zhang@...wei.com, 
	houtao1@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH v2 2/2] md: don't account sync_io if iostats of the disk
 is disabled

On Thu, Dec 14, 2023 at 5:41 PM <linan666@...weicloud.com> wrote:
>
> From: Li Nan <linan122@...wei.com>
>
> If iostats is disabled, disk_stats will not be updated and
> part_stat_read_accum() only returns a constant value. In this case,
> continuing to count sync_io and to check is_mddev_idle() is no longer
> meaningful.
>
> Signed-off-by: Li Nan <linan122@...wei.com>
> ---
>  drivers/md/md.h | 3 ++-
>  drivers/md/md.c | 4 ++++
>  2 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index 1a4f976951c1..75f5c5d04e71 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -589,7 +589,8 @@ static inline void md_sync_acct(struct block_device *bdev, unsigned long nr_sect
>
>  static inline void md_sync_acct_bio(struct bio *bio, unsigned long nr_sectors)
>  {
> -       md_sync_acct(bio->bi_bdev, nr_sectors);
> +       if (blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
> +               md_sync_acct(bio->bi_bdev, nr_sectors);

Do we need the same check for md_sync_acct()?

>  }
>
>  struct md_personality
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 1d71b2a9af03..18bbceb0ffd6 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -8502,6 +8502,10 @@ static int is_mddev_idle(struct mddev *mddev, int init)
>         rcu_read_lock();
>         rdev_for_each_rcu(rdev, mddev) {
>                 struct gendisk *disk = rdev->bdev->bd_disk;
> +
> +               if (blk_queue_io_stat(mddev->queue))
> +                       continue;

This looks weird. Do you mean

   if (!blk_queue_io_stat(disk->queue))

Note that I changed two things here: 1) add "!"; 2) check disk, not mddev.

Did I miss something?

Thanks,
Song

> +
>                 curr_events =
>                         (long long)part_stat_read_accum(disk->part0, sectors) -
>                               atomic64_read(&disk->sync_io);
> --
> 2.39.2
>