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Message-ID: <d766a9cc-df46-5f0c-184d-19f4b9b2a8b7@huaweicloud.com>
Date: Wed, 3 Jan 2024 14:35:32 +0800
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Subject: Re: [PATCH v3 2/2] md: don't account sync_io if iostats of the disk
 is disabled
To: Yu Kuai <yukuai1@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>
 <e2305cc4-dc3e-7693-9b61-33896c1b7a37@huaweicloud.com>
From: Li Nan <linan666@huaweicloud.com>
In-Reply-To: <e2305cc4-dc3e-7693-9b61-33896c1b7a37@huaweicloud.com>
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在 2024/1/3 11:16, Yu Kuai 写道:
> 
> 
> 在 2023/12/23 11:37, linan666@huaweicloud.com 写道:
>> 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 for your review, I will add checks of 'init' in next version.

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

-- 
Thanks,
Nan