linux-kernel - Re: [PATCH] loop: inherit the ioprio in loop woker thread

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Date: Wed, 22 May 2024 12:13:53 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Bart Van Assche <bvanassche@....org>,
 Yunlong Xing <yunlong.xing@...soc.com>, yunlongxing23@...il.com,
 niuzhiguo84@...il.com, Hao_hao.Wang@...soc.com
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] loop: inherit the ioprio in loop woker thread

On 5/22/24 12:12 PM, Bart Van Assche wrote:
> On 5/22/24 10:57, Jens Axboe wrote:
>> On 5/22/24 11:38 AM, Bart Van Assche wrote:
>>> On 5/22/24 00:48, Yunlong Xing wrote:
>>>> @@ -1913,6 +1921,10 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
>>>>            set_active_memcg(old_memcg);
>>>>            css_put(cmd_memcg_css);
>>>>        }
>>>> +
>>>> +    if (ori_ioprio != cmd_ioprio)
>>>> +        set_task_ioprio(current, ori_ioprio);
>>>> +
>>>>     failed:
>>>>        /* complete non-aio request */
>>>>        if (!use_aio || ret) {
>>>
>>> Does adding this call in the hot path have a measurable performance impact?
>>
>> It's loop, I would not be concerned with overhead. But it does look pretty
>> bogus to modify the task ioprio from here.
> 
> Hi Jens,
> 
> Maybe Yunlong uses that call to pass the I/O priority to the I/O submitter?
> 
> I think that it is easy to pass the I/O priority to the kiocb submitted by
> lo_rw_aio() without calling set_task_ioprio().

Yeah that was my point, it's both the completely wrong way to do it, nor
is it a sane way to do it. If the current stack off that doesn't allow
priority to be passed, then that work would need to be done first.

-- 
Jens Axboe