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Subject: Re: [PATCH v3 2/2] md: don't account sync_io if iostats of the disk
 is disabled
To: linan666@huaweicloud.com, song@kernel.org, axboe@kernel.dk
Cc: linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
 linux-block@vger.kernel.org, yi.zhang@huawei.com, houtao1@huawei.com,
 yangerkun@huawei.com, "yukuai (C)" <yukuai3@huawei.com>
References: <20231223033703.2949831-1-linan666@huaweicloud.com>
 <20231223033703.2949831-3-linan666@huaweicloud.com>
From: Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <e2305cc4-dc3e-7693-9b61-33896c1b7a37@huaweicloud.com>
Date: Wed, 3 Jan 2024 11:16:13 +0800
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?? 2023/12/23 11:37, linan666@huaweicloud.com д??:
> From: Li Nan <linan122@huawei.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@huawei.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..e2d03a7a858c 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -584,7 +584,8 @@ extern void mddev_unlock(struct mddev *mddev);
>   
>   static inline void md_sync_acct(struct block_device *bdev, unsigned long nr_sectors)
>   {
> -	atomic64_add(nr_sectors, &bdev->bd_disk->sync_io);
> +	if (blk_queue_io_stat(bdev->bd_disk->queue))
> +		atomic64_add(nr_sectors, &bdev->bd_disk->sync_io);
>   }
>   
>   static inline void md_sync_acct_bio(struct bio *bio, unsigned long nr_sectors)
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index a6829ea5b560..b56614eae8dc 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(disk->queue))
> +			continue;

Consider that the queue flag can be set/cleared through sysfs, let's
keep set rdev->last_events in the case 'init'. To prevent a false
positive(althrough highly unlikely) if iostat is enabled during
md_do_sync().

Thanks,
Kuai

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