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 17:29:17 +0800
From: Li Nan <linan666@...weicloud.com>
To: Song Liu <song@...nel.org>, 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



在 2023/12/15 17:08, Song Liu 写道:
> 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
> 

Yeah... It's my bad. I will fix it in v3.

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

-- 
Thanks,
Nan