linux-kernel - Re: Re: [PATCH v5] io_uring: Statistics of the true utilization of sq threads.

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Message-Id: <20231222083530.11051-1-xiaobing.li@samsung.com>
Date: Fri, 22 Dec 2023 16:35:30 +0800
From: Xiaobing Li <xiaobing.li@...sung.com>
To: axboe@...nel.dk
Cc: asml.silence@...il.com, linux-kernel@...r.kernel.org,
	io-uring@...r.kernel.org, kun.dou@...sung.com, peiwei.li@...sung.com,
	joshi.k@...sung.com, kundan.kumar@...sung.com, wenwen.chen@...sung.com,
	ruyi.zhang@...sung.com, xiaobing.li@...sung.com
Subject: Re: Re: [PATCH v5] io_uring: Statistics of the true utilization of
 sq threads.

On 12/18/23 15:53, Jens Axboe wrote:
> I think I'm convinced that the effectiveness of the chosen SQPOLL
> settings being exposed is useful, I'm just not sure fdinfo is the right
> place to do it. Is it going to be a problem that these are just
> perpetual stats, with no way to reset them? This means there's no way to
> monitor it for a period of time and get effectiveness for something
> specific, it'll always just count from when the ring was created.
> 
> We could of course have the act of reading the stat also reset it, but
> maybe that'd be a bit odd?
> 
> Alternatively, it could be exported differently, eg as a register opcode
> perhaps.
> 
> Open to suggestions...

I thought carefully about your proposed reset stat, and I think it can be 
achieved by outputting "work_time" and "total_time".
eg:
Output at time t1:
SqMask: 0x3
SqHead: 1168417
SqTail: 1168418
SqWorkTime: t1_work
SqTotalTime: t1_total

Output at time t2:
SqMask: 0x3
SqHead: 1168417
SqTail: 1168418
SqWorkTime: t2_work
SqTotalTime: t2_total

Then we can manually calculate the utilization rate from t1 to t2:
(t2_work - t1_work) / (t2_total - t1_total)

Not sure what you think, but if you think it doesn't work, I'll look into 
other good ways to add the ability to reset.

In addition, on register opcode - generally it is used for resource like
buffers, handles etc.. I am not sure how that can help here. If you have
something in mind, could you please elaborate in more detail?