linux-kernel - Re: Re: io_uring: releasing CPU resources when polling.

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Date: Thu, 18 Apr 2024 14:07:16 +0800
From: hexue <xue01.he@...sung.com>
To: axboe@...nel.dk
Cc: anuj20.g@...sung.com, asml.silence@...il.com, cliang01.li@...sung.com,
	io-uring@...r.kernel.org, joshi.k@...sung.com, kundan.kumar@...sung.com,
	linux-kernel@...r.kernel.org, peiwei.li@...sung.com, ruyi.zhang@...sung.com,
	wenwen.chen@...sung.com, xiaobing.li@...sung.com, xue01.he@...sung.com
Subject: Re: Re: io_uring: releasing CPU resources when polling.

On 3/26/24  3:39, Jens Axboe wrote:
>On 3/25/24 9:23 PM, Xue wrote:
>> Hi,
>> 
>> I hope this message finds you well.
>> 
>> I'm waiting to follow up on the patch I submitted on 3.18,
>> titled "io_uring: releasing CPU resources when polling".
>> 
>> I haven't received feedback yet and wondering if you had
>> a chance to look at it. Any guidance or suggestions you could
>> provide would be greatly appreciated.
>
>I did take a look at it, and I have to be honest - I don't like it at
>all. It's a lot of expensive code in the fast path, for a problem that
>should not really exist. The system is misconfigured if you're doing
>polled IO for devices that don't have a poll queue. At some point the
>block layer returned -EOPNOTSUPP for that, and honestly I think that's a
>MUCH better solution than adding expensive code in the fast path for
>something that is really a badly configured setup.

Sorry for my late reply, if you think that the scenario where if you're 
doing polled IO for devices that don't have a poll queue is just a 
misconfigured and does not need to be changed too much, then I'm inclined
to extend this scenario to all devices, I think it's an effective way to
release CPU resources, and I verified this and found that it does have a
very good benefit. At the same time I have reduce the code in the fast
path. I will release the v2 version of the code with my test results,
and please reconsider the feasibility of this solution.

--
Xue