linux-kernel - Re: [PATCH v3 2/2] md: don't account sync_io if iostats of the disk is disabled

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Date: Wed, 3 Jan 2024 14:35:32 +0800
From: Li Nan <linan666@...weicloud.com>
To: Yu Kuai <yukuai1@...weicloud.com>, song@...nel.org, axboe@...nel.dk
Cc: linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-block@...r.kernel.org, yi.zhang@...wei.com, houtao1@...wei.com,
 yangerkun@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v3 2/2] md: don't account sync_io if iostats of the disk
 is disabled



在 2024/1/3 11:16, Yu Kuai 写道:
> 
> 
> 在 2023/12/23 11:37, linan666@...weicloud.com 写道:
>> 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..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