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

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Date: Mon, 25 Mar 2024 21:39:25 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Xue <xue01.he@...sung.com>
Cc: asml.silence@...il.com, linux-kernel@...r.kernel.org,
 io-uring@...r.kernel.org, peiwei.li@...sung.com, joshi.k@...sung.com,
 kundan.kumar@...sung.com, anuj20.g@...sung.com, wenwen.chen@...sung.com,
 ruyi.zhang@...sung.com, xiaobing.li@...sung.com, cliang01.li@...sung.com
Subject: Re: io_uring: releasing CPU resources when polling

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.

-- 
Jens Axboe