linux-kernel - Re: [PATCH v7] io_uring: Statistics of the true utilization of sq threads.

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Date: Mon, 29 Jan 2024 15:01:43 +0000
From: Pavel Begunkov <asml.silence@...il.com>
To: Xiaobing Li <xiaobing.li@...sung.com>, axboe@...nel.dk
Cc: 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
Subject: Re: [PATCH v7] io_uring: Statistics of the true utilization of sq
 threads.

On 1/29/24 07:18, Xiaobing Li wrote:
> On 1/18/24 19:34, Jens Axboe wrote:
>>> diff --git a/io_uring/sqpoll.h b/io_uring/sqpoll.h
>>> index 8df37e8c9149..c14c00240443 100644
>>> --- a/io_uring/sqpoll.h
>>> +++ b/io_uring/sqpoll.h
>>> @@ -16,6 +16,7 @@ struct io_sq_data {
>>>   	pid_t			task_pid;
>>>   	pid_t			task_tgid;
>>>   
>>> +	long long			work_time;
>>>   	unsigned long		state;
>>>   	struct completion	exited;
>>>   };
>>
>> Probably just make that an u64.
>>
>> As Pavel mentioned, I think we really need to consider if fdinfo is the
>> appropriate API for this. It's fine if you're running stuff directly and
>> you're just curious, but it's a very cumbersome API in general as you
>> need to know the pid of the task holding the ring, the fd of the ring,
>> and then you can get it as a textual description. If this is something
>> that is deemed useful, would it not make more sense to make it
>> programatically available in addition, or even exclusively?
> 
> Hi, Jens and Pavel
> sorry for the late reply.
> 
> I've tried some other methods, but overall, I haven't found a more suitable
> method than fdinfo.

I wouldn't mind if it's fdinfo only for now, that can be changed later
if needed. I'm more concerned that reading fdinfo and then parsing it
is incompatible with the word performance, which you mentioned in the
context of using 1 vs 2 syscalls to get the stats.

That can be left to be resolved later, however. Let's just be clear
in docs that stats could be 0, which means the feature is not
working/disabled.

Another question I raised in my reply (v6 thread), why it's using
ktime_get(), which same as jiffies but more precise, instead of a
task time?

> If you think it is troublesome to obtain the PID,  then I can provide

I missed the context, where do we need to know PIDs?

>   a shell script to output the total_time and work_time of all sqpoll threads
>   to the terminal, so that we do not have to manually obtain the PID of each
>   thread (the script can be placed in tools/ include/io_uring).
> 
> eg:
> 
> PID    WorkTime(us)   TotalTime(us)   COMMAND
> 9330   1106578        2215321         iou-sqp-9329
> 9454   1510658        1715321         iou-sqp-9453
> 9478   165785         223219          iou-sqp-9477
> 9587   106578         153217          iou-sqp-9586
> 
> What do you think of this solution?

-- 
Pavel Begunkov