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

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Date: Thu, 18 Jan 2024 12:34:24 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Xiaobing Li <xiaobing.li@...sung.com>, asml.silence@...il.com
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,
 cliang01.li@...sung.com, xue01.he@...sung.com
Subject: Re: [PATCH v7] io_uring: Statistics of the true utilization of sq
 threads.

On 1/18/24 12:30 AM, Xiaobing Li wrote:
> diff --git a/io_uring/fdinfo.c b/io_uring/fdinfo.c
> index 976e9500f651..24a7452ed98e 100644
> --- a/io_uring/fdinfo.c
> +++ b/io_uring/fdinfo.c
> @@ -64,6 +64,7 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *f)
>  	unsigned int sq_shift = 0;
>  	unsigned int sq_entries, cq_entries;
>  	int sq_pid = -1, sq_cpu = -1;
> +	long long sq_total_time = 0, sq_work_time = 0;
>  	bool has_lock;
>  	unsigned int i;
>  
> @@ -147,10 +148,17 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *f)
>  
>  		sq_pid = sq->task_pid;
>  		sq_cpu = sq->sq_cpu;
> +		struct rusage r;
> +
> +		getrusage(sq->thread, RUSAGE_SELF, &r);
> +		sq_total_time = r.ru_stime.tv_sec * 1000000 + r.ru_stime.tv_usec;
> +		sq_work_time = sq->work_time;
>  	}

I guess getrusage() is fine here, though I would probably just grab it
directly.

> diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
> index 65b5dbe3c850..f3e9fda72400 100644
> --- a/io_uring/sqpoll.c
> +++ b/io_uring/sqpoll.c
> @@ -251,6 +251,9 @@ static int io_sq_thread(void *data)
>  		}
>  
>  		cap_entries = !list_is_singular(&sqd->ctx_list);
> +		ktime_t start, diff;
> +
> +		start = ktime_get();
>  		list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
>  			int ret = __io_sq_thread(ctx, cap_entries);

But why on earth is this part then not doing getrusage() as well?

> 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?

-- 
Jens Axboe