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Message-ID: <d9795483-ef64-4fd6-be71-a3946ae8fb3e@kernel.dk>
Date: Wed, 22 May 2024 12:13:53 -0600
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Subject: Re: [PATCH] loop: inherit the ioprio in loop woker thread
To: Bart Van Assche <bvanassche@acm.org>,
 Yunlong Xing <yunlong.xing@unisoc.com>, yunlongxing23@gmail.com,
 niuzhiguo84@gmail.com, Hao_hao.Wang@unisoc.com
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20240522074829.1750204-1-yunlong.xing@unisoc.com>
 <5166bc31-1fd9-4f7f-bc51-f1f50d9d5483@acm.org>
 <68cfbc08-6d39-4bc6-854d-5df0c94dbfd4@kernel.dk>
 <f6d3e1f2-e004-49bb-b6c1-969915ccab37@acm.org>
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From: Jens Axboe <axboe@kernel.dk>
In-Reply-To: <f6d3e1f2-e004-49bb-b6c1-969915ccab37@acm.org>
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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