linux-kernel - Re: [blk] 8c5035dfbb: fio.read

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Date:   Sun, 9 Oct 2022 17:32:34 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Ming Lei <ming.lei@...hat.com>, Yu Kuai <yukuai1@...weicloud.com>
Cc:     kernel test robot <yujie.liu@...el.com>, lkp@...ts.01.org,
        lkp@...el.com, Jens Axboe <axboe@...nel.dk>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        ying.huang@...el.com, feng.tang@...el.com,
        zhengjun.xing@...ux.intel.com, fengwei.yin@...el.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [blk] 8c5035dfbb: fio.read_iops -10.6% regression

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
> 
> .
>