Subject: Re: [PATCH -next RFC] block: count 'ios' and 'sectors' when io is
 done for bio-based device
To:     Yu Kuai <yukuai1@huaweicloud.com>, axboe@kernel.dk, agk@redhat.com,
        snitzer@kernel.org, dm-devel@redhat.com, kbusch@kernel.org,
        hch@lst.de, sagi@grimberg.me, guz.fnst@cn.fujitsu.com
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, yi.zhang@huawei.com,
        yangerkun@huawei.com, "yukuai (C)" <yukuai3@huawei.com>
References: <20230223091226.1135678-1-yukuai1@huaweicloud.com>
 <05bbc421-100c-c18d-4261-e5669cfdfb94@huaweicloud.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <a4d8f6b5-cc8e-204e-1039-5f2b98042bdd@huaweicloud.com>
Date:   Tue, 7 Mar 2023 18:44:49 +0800
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Hi,

在 2023/02/28 9:01, Yu Kuai 写道:
> Hi,
> 
> friendly ping ...
> 
> Thanks,
> Kuai
> 
> 在 2023/02/23 17:12, Yu Kuai 写道:
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> While using iostat for raid, I observed very strange 'await'
>> occasionally, and turns out it's due to that 'ios' and 'sectors' is
>> counted in bdev_start_io_acct(), while 'nsecs' is counted in
>> bdev_end_io_acct(). I'm not sure why they are ccounted like that
>> but I think this behaviour is obviously wrong because user will get
>> wrong disk stats.
>>
>> Fix the problem by counting 'ios' and 'sectors' when io is done, like
>> what rq-based device does.

Can anyone help to review this change? Or is there any reason to count
'ios' and 'sectors' when io is started?

Thanks,
Kuai
>>
>> Fixes: 394ffa503bc4 ("blk: introduce generic io stat accounting help 
>> function")
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>> ---
>>   block/blk-core.c              | 16 ++++++----------
>>   drivers/md/dm.c               |  6 +++---
>>   drivers/nvme/host/multipath.c |  8 ++++----
>>   include/linux/blkdev.h        |  5 ++---
>>   4 files changed, 15 insertions(+), 20 deletions(-)
>>
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index 82b5b2c53f1e..fe1d320f5f07 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -953,16 +953,11 @@ void update_io_ticks(struct block_device *part, 
>> unsigned long now, bool end)
>>       }
>>   }
>> -unsigned long bdev_start_io_acct(struct block_device *bdev,
>> -                 unsigned int sectors, enum req_op op,
>> +unsigned long bdev_start_io_acct(struct block_device *bdev, enum 
>> req_op op,
>>                    unsigned long start_time)
>>   {
>> -    const int sgrp = op_stat_group(op);
>> -
>>       part_stat_lock();
>>       update_io_ticks(bdev, start_time, false);
>> -    part_stat_inc(bdev, ios[sgrp]);
>> -    part_stat_add(bdev, sectors[sgrp], sectors);
>>       part_stat_local_inc(bdev, in_flight[op_is_write(op)]);
>>       part_stat_unlock();
>> @@ -978,13 +973,12 @@ EXPORT_SYMBOL(bdev_start_io_acct);
>>    */
>>   unsigned long bio_start_io_acct(struct bio *bio)
>>   {
>> -    return bdev_start_io_acct(bio->bi_bdev, bio_sectors(bio),
>> -                  bio_op(bio), jiffies);
>> +    return bdev_start_io_acct(bio->bi_bdev, bio_op(bio), jiffies);
>>   }
>>   EXPORT_SYMBOL_GPL(bio_start_io_acct);
>>   void bdev_end_io_acct(struct block_device *bdev, enum req_op op,
>> -              unsigned long start_time)
>> +              unsigned int sectors, unsigned long start_time)
>>   {
>>       const int sgrp = op_stat_group(op);
>>       unsigned long now = READ_ONCE(jiffies);
>> @@ -992,6 +986,8 @@ void bdev_end_io_acct(struct block_device *bdev, 
>> enum req_op op,
>>       part_stat_lock();
>>       update_io_ticks(bdev, now, true);
>> +    part_stat_inc(bdev, ios[sgrp]);
>> +    part_stat_add(bdev, sectors[sgrp], sectors);
>>       part_stat_add(bdev, nsecs[sgrp], jiffies_to_nsecs(duration));
>>       part_stat_local_dec(bdev, in_flight[op_is_write(op)]);
>>       part_stat_unlock();
>> @@ -1001,7 +997,7 @@ EXPORT_SYMBOL(bdev_end_io_acct);
>>   void bio_end_io_acct_remapped(struct bio *bio, unsigned long 
>> start_time,
>>                     struct block_device *orig_bdev)
>>   {
>> -    bdev_end_io_acct(orig_bdev, bio_op(bio), start_time);
>> +    bdev_end_io_acct(orig_bdev, bio_op(bio), bio_sectors(bio), 
>> start_time);
>>   }
>>   EXPORT_SYMBOL_GPL(bio_end_io_acct_remapped);
>> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
>> index eace45a18d45..f5cc330bb549 100644
>> --- a/drivers/md/dm.c
>> +++ b/drivers/md/dm.c
>> @@ -512,10 +512,10 @@ static void dm_io_acct(struct dm_io *io, bool end)
>>           sectors = io->sectors;
>>       if (!end)
>> -        bdev_start_io_acct(bio->bi_bdev, sectors, bio_op(bio),
>> -                   start_time);
>> +        bdev_start_io_acct(bio->bi_bdev, bio_op(bio), start_time);
>>       else
>> -        bdev_end_io_acct(bio->bi_bdev, bio_op(bio), start_time);
>> +        bdev_end_io_acct(bio->bi_bdev, bio_op(bio), sectors,
>> +                 start_time);
>>       if (static_branch_unlikely(&stats_enabled) &&
>>           unlikely(dm_stats_used(&md->stats))) {
>> diff --git a/drivers/nvme/host/multipath.c 
>> b/drivers/nvme/host/multipath.c
>> index fc39d01e7b63..9171452e2f6d 100644
>> --- a/drivers/nvme/host/multipath.c
>> +++ b/drivers/nvme/host/multipath.c
>> @@ -123,9 +123,8 @@ void nvme_mpath_start_request(struct request *rq)
>>           return;
>>       nvme_req(rq)->flags |= NVME_MPATH_IO_STATS;
>> -    nvme_req(rq)->start_time = bdev_start_io_acct(disk->part0,
>> -                    blk_rq_bytes(rq) >> SECTOR_SHIFT,
>> -                    req_op(rq), jiffies);
>> +    nvme_req(rq)->start_time = bdev_start_io_acct(disk->part0, 
>> req_op(rq),
>> +                              jiffies);
>>   }
>>   EXPORT_SYMBOL_GPL(nvme_mpath_start_request);
>> @@ -136,7 +135,8 @@ void nvme_mpath_end_request(struct request *rq)
>>       if (!(nvme_req(rq)->flags & NVME_MPATH_IO_STATS))
>>           return;
>>       bdev_end_io_acct(ns->head->disk->part0, req_op(rq),
>> -        nvme_req(rq)->start_time);
>> +             blk_rq_bytes(rq) >> SECTOR_SHIFT,
>> +             nvme_req(rq)->start_time);
>>   }
>>   void nvme_kick_requeue_lists(struct nvme_ctrl *ctrl)
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index d1aee08f8c18..941304f17492 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -1446,11 +1446,10 @@ static inline void blk_wake_io_task(struct 
>> task_struct *waiter)
>>           wake_up_process(waiter);
>>   }
>> -unsigned long bdev_start_io_acct(struct block_device *bdev,
>> -                 unsigned int sectors, enum req_op op,
>> +unsigned long bdev_start_io_acct(struct block_device *bdev, enum 
>> req_op op,
>>                    unsigned long start_time);
>>   void bdev_end_io_acct(struct block_device *bdev, enum req_op op,
>> -        unsigned long start_time);
>> +              unsigned int sectors, unsigned long start_time);
>>   unsigned long bio_start_io_acct(struct bio *bio);
>>   void bio_end_io_acct_remapped(struct bio *bio, unsigned long 
>> start_time,
>>
> 
> .
>