[PATCH] Add io_uring support in AIO(async io) module

[Zhao, Ping]

Hi Vladimir,

No special/extra configuration needed, but need check if 'aio on' and 'sendfile off' is correctly set. This is my Nginx config for reference:

user nobody;
daemon off;
worker_processes 1;
error_log error.log ;
events {
    worker_connections 65535;
    use epoll;
}

http {
    include mime.types;
    default_type application/octet-stream;
    access_log on;
    aio on;
    sendfile off;
    directio 2k;

    # Cache Configurations
    proxy_cache_path /mnt/cache0 levels=2 keys_zone=nginx-cache0:400m max_size=1400g inactive=4d use_temp_path=off;
......


To better measure the disk io performance data, I do the following steps:
1. To exclude other impact, and focus on disk io part.(This patch only impact disk aio read process) Use cgroup to limit Nginx memory usage. Otherwise Nginx may also use memory as cache storage and this may cause test result not so straight.(since most cache hit in memory, disk io bw is low, like my previous mail found which didn't exclude the memory cache impact)
     echo 2G > memory.limit_in_bytes
     use ' cgexec -g memory:nginx' to start Nginx.

2. use wrk -t 100 -c 1000, with random 25000 http requests. 
     My previous test used -t 200 connections, comparing with -t 1000, libaio performance drop more when connections numbers increased from 200 to 1000, but io_uring doesn't. It's another advantage of io_uring.

3. First clean the cache disk and run the test for 30 minutes to let Nginx store the cache files to nvme disk as much as possible.

4. Rerun the test, this time Nginx will use ngx_file_aio_read to extract the cache files in nvme cache disk. Use iostat to track the io data. The data should be align with NIC bw since all data should be from cache disk.(need exclude memory as cache storage impact)

Following is the test result:

Nginx worker_processes 1:
		4k		100k		1M
Io_uring	220MB/s	1GB/s		1.3GB/s
Libaio		70MB/s		250MB/s	600MB/s(with -c 200, 1.0GB/s)


Nginx worker_processes 4:
		4k		100k		1M
Io_uring	800MB/s	2.5GB/s		2.6GB/s(my nvme disk io maximum bw)
libaio		250MB/s	900MB/s	2.0GB/s

So for small request, io_uring has huge improvement than libaio. In previous mail, because I didn't exclude the memory cache storage impact, most cache file is stored in memory, very few are from disk in case of 4k/100k. The data is not correct.(for 1M, because the cache is too big to store in memory, it wat in disk)  Also I enabled directio option "directio 2k" this time to avoid this.

Regards,
Ping

-----Original Message-----
From: nginx-devel <nginx-devel-bounces at nginx.org> On Behalf Of Vladimir Homutov
Sent: Wednesday, January 20, 2021 12:43 AM
To: nginx-devel at nginx.org
Subject: Re: [PATCH] Add io_uring support in AIO(async io) module

On Tue, Jan 19, 2021 at 03:32:30AM +0000, Zhao, Ping wrote:
> It depends on if disk io is the performance hot spot or not. If yes, 
> io_uring shows improvement than libaio. With 4KB/100KB length 1 Nginx 
> thread it's hard to see performance difference because iostat is only 
> around ~10MB/100MB per second. Disk io is not the performance bottle 
> neck, both libaio and io_uring have the same performance. If you 
> increase request size or Nginx threads number, for example 1MB length 
> or Nginx thread number 4. In this case, disk io became the performance 
> bottle neck, you will see io_uring performance improvement.

Can you please provide full test results with specific nginx configuration?

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