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Subject: Re: [blk] 8c5035dfbb: fio.read_iops -10.6% regression
To:     Ming Lei <ming.lei@redhat.com>, Yu Kuai <yukuai1@huaweicloud.com>
Cc:     kernel test robot <yujie.liu@intel.com>, lkp@lists.01.org,
        lkp@intel.com, Jens Axboe <axboe@kernel.dk>,
        linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
        ying.huang@intel.com, feng.tang@intel.com,
        zhengjun.xing@linux.intel.com, fengwei.yin@intel.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <202210081045.77ddf59b-yujie.liu@intel.com>
 <d5279fc2-38b3-6d20-4404-604d5c7277e2@huaweicloud.com>
 <Y0KJmODYOh83OtGa@T590>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <e81ea0fe-dcd2-1e5d-9b78-3c79751b3097@huaweicloud.com>
Date:   Sun, 9 Oct 2022 17:32:34 +0800
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Hi,

在 2022/10/09 16:43, Ming Lei 写道:
> On Sat, Oct 08, 2022 at 04:00:10PM +0800, Yu Kuai wrote:
>> Hi,
>>
>> 在 2022/10/08 10:50, kernel test robot 写道:
>>> Greeting,
>>>
>>> FYI, we noticed a -10.6% regression of fio.read_iops due to commit:
>>
>> I don't know how this is working but I'm *sure* this commit won't affect
> 
> Looks it is wrong to move
> 
> 	wbt_set_write_cache(q, test_bit(QUEUE_FLAG_WC, &q->queue_flags));
> 
> before rq_qos_add() in wbt_init().
> 
> Without adding wbt rq_qos, wbt_set_write_cache is just a nop.

Yes, I got it now, I'm being foolish here.

I missed that "rwb->wc" is got by rq_qos in wbt_set_write_cache(), which
is NULL before rq_qos_add(). By the way, it's interesting that how read
performance is affected, I still don't know why yet...

Thanks,
Kuai
> 
> 
> thanks,
> Ming
> 
> .
>