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Message-ID: <288f846f-01f7-6c60-b440-aaabb1538de3@huaweicloud.com>
Date:   Sat, 10 Jun 2023 16:42:02 +0800
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Subject: Re: [PATCH] md/raid10: Only check QUEUE_FLAG_IO_STAT when issuing io
To:     Yu Kuai <yukuai1@huaweicloud.com>, linan666@huaweicloud.com,
        song@kernel.org, jgq516@gmail.com
Cc:     linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, houtao1@huawei.com, yangerkun@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20230609094320.2397604-1-linan666@huaweicloud.com>
 <8d2134a6-90dc-822b-52ef-cd7cc8060b36@huaweicloud.com>
From:   Li Nan <linan666@huaweicloud.com>
In-Reply-To: <8d2134a6-90dc-822b-52ef-cd7cc8060b36@huaweicloud.com>
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在 2023/6/10 10:32, Yu Kuai 写道:
> Hi,
> 
> 在 2023/06/09 17:43, linan666@huaweicloud.com 写道:
>> From: Li Nan <linan122@huawei.com>
>>
>> /sys/block/[device]/queue/iostats is used to control whether to count io
>> stat. Write 0 to it will clear queue_flags QUEUE_FLAG_IO_STAT which means
>> iostats is disabled. If we disable iostats and later endable it, the io
>> issued during this period will be counted incorrectly, inflight will be
>> decreased to -1.
>>
>>    //T1 set iostats
>>    echo 0 > /sys/block/md0/queue/iostats
>>     clear QUEUE_FLAG_IO_STAT
>>
>>             //T2 issue io
>>             if (QUEUE_FLAG_IO_STAT) -> false
>>              bio_start_io_acct
>>               inflight++
>>
>>    echo 1 > /sys/block/md0/queue/iostats
>>     set QUEUE_FLAG_IO_STAT
>>
>>                     //T3 io end
>>                     if (QUEUE_FLAG_IO_STAT) -> true
>>                      bio_end_io_acct
>>                       inflight--    -> -1
>>
>> Also, if iostats is enabled while issuing io but disabled while io end,
>> inflight will never be decreased.
>>
>> Fix it by checking start_time when io end. Only check QUEUE_FLAG_IO_STAT
>> while issuing io, just like request based devices.
>>
>> Fixes: 528bc2cf2fcc ("md/raid10: enable io accounting")
>> Signed-off-by: Li Nan <linan122@huawei.com>
>> ---
>>   drivers/md/raid10.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
>> index 381c21f7fb06..bf9dca5c25c3 100644
>> --- a/drivers/md/raid10.c
>> +++ b/drivers/md/raid10.c
>> @@ -325,7 +325,7 @@ static void raid_end_bio_io(struct r10bio *r10_bio)
>>       if (!test_bit(R10BIO_Uptodate, &r10_bio->state))
>>           bio->bi_status = BLK_STS_IOERR;
>> -    if (blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
>> +    if (r10_bio->start_time)
>>           bio_end_io_acct(bio, r10_bio->start_time);
> 
> This patch LGTM, can you change this for raid1 as well? raid0 and
> raid456 is using md_account_bio(), and they don't have such problem.
> 

OK, I will fix raid1 later. Thanks for suggestion.

> Thanks,
> Kuai
-- 
Thanks,
Nan