Implement io_uring support for FileStream

[adamsitnik]

We have recently invested a lot of time in rewriting FileStream on Windows. We have kept io_uring in mind and after recent refactoring, it should be now much easier to implement the support:

• we have introduced a new internal abstraction called FileStreamStrategy. It's more or less FileStream API.
• FileStream can choose the strategy at runtime. In the case of Linux, it could detect the kernel version and just use the new strategy for newer kernels (5.5+). It means that the day our customers update their kernel version, .NET could start using io_uring without a .NET update.
• Entire buffering logic has been moved to a new strategy called BufferedFileStreamStrategy which can be used as a wrapper over another strategy. It means that new strategies (like IoUringStrategy) don't need to worry about buffering at all
  

  runtime/src/libraries/System.Private.CoreLib/src/System/IO/Strategies/FileStreamHelpers.Windows.cs

  Lines 59 to 60 in 2223bab

  	internal static FileStreamStrategy EnableBufferingIfNeeded(WindowsFileStreamStrategy strategy, int bufferSize)
  	=> bufferSize == 1 ? strategy : new BufferedFileStreamStrategy(strategy, bufferSize);

• We can use the existing Unix strategy for sync file IO, so the new IoUringStrategy would only need to implement ReadAsync and WriteAsync support.

We (owners of System.IO) have a lot of other high-priority things on our schedule for .NET 6 (like full symbolic links support) and since most of our customers are not using the latest Linux kernels, we are most probably won't be able to implement it on our own for .NET 6. But we would love to provide any help necessary (code reviews, testing) for a contributor that would be willing to implement it. Having said that, I am marking this issue as "up-for-grabs".

If we won't find a contributor for .NET 6, we are going to include this in .NET 7 planning and deliver it in .NET 7.

Tagging subscribers to this area: @carlossanlop
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Issue Details

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We have recently invested a lot of time in rewriting FileStream on Windows. We have kept io_uring in mind and after recent refactoring, it should be now much easier to implement the support:

• we have introduced a new internal abstraction called FileStreamStrategy. It's more or less FileStream API.
• FileStream can choose the strategy at runtime. In the case of Linux, it could detect the kernel version and just use the new strategy for newer kernels (5.5+). It means that the day our customers update their kernel version, .NET could start using io_uring without a .NET update.
• Entire buffering logic has been moved to a new strategy called BufferedFileStreamStrategy which can be used as a wrapper over another strategy. It means that new strategies (like IoUringStrategy) don't need to worry about buffering at all
  

  runtime/src/libraries/System.Private.CoreLib/src/System/IO/Strategies/FileStreamHelpers.Windows.cs

  Lines 59 to 60 in 2223bab

  	internal static FileStreamStrategy EnableBufferingIfNeeded(WindowsFileStreamStrategy strategy, int bufferSize)
  	=> bufferSize == 1 ? strategy : new BufferedFileStreamStrategy(strategy, bufferSize);

• We can use the existing Unix strategy for sync file IO, so the new IoUringStrategy would only need to implement ReadAsync and WriteAsync support.

We (owners of System.IO) have a lot of other high-priority things on our schedule for .NET 6 (like full symbolic links support) and since most of our customers are not using the latest Linux kernels, we are most probably won't be able to implement it on our own for .NET 6. But we would love to provide any help necessary (code reviews, testing) for a contributor that would be willing to implement it. Having said that, I am marking this issue as "up-for-grabs".

If we won't find a contributor for .NET 6, we are going to include this in .NET 7 planning and deliver it in .NET 7.

Author:	adamsitnik
Assignees:	-
Labels:	area-System.IO, tenet-performance, up-for-grabs
Milestone:	Future

[adamsitnik]

@tmds @damageboy @benaadams would any of you be interested?

[tmds]

Many of the io_uring benchmarks are performed on a single thread that needs no synchronization. We won't be able to achieve the gains measured there because we need to synchronize and hop between threads. That will definitely cost us something.

Functionally, using io_uring allows to cancel the the on-going operations. This is not supported with the current sync-on-ThreadPool implementation. So this is a functional gain.

I'll let you know if I find time to work on this. I'd need your, and others, help to optimize the thread/synchronization stuff.

[richlander]

it could detect the kernel version and just use the new strategy for newer kernels (5.5+)

I thought in our last conversation we decided that we should gate this feature on 5.10 since the support between 5.5 and 5.7 is patchy. It seems like 5.10 would be great. As context, .NET 6 container images use Debian 11 by default and the second most popular are Alpine, which for .NET 6 will be 3.13+.

Here's what I found on kernel versions.

• Alpine 3.13: 5.10
• Arch Linux 2021.05.01: 5.11
• Debian 10: 4.x
• Debian 11: 5.10
• Red Hat 8: 4.x
• Ubuntu 20.04: 5.4
• Ubuntu 21.04: 5.11

Interesting context: https://news.ycombinator.com/item?id=27382299

[omariom]

WSL is already 5.4.72-microsoft-standard-WSL2

[ayousuf23]

@adamsitnik What is io_uring? Is it a new algorithm for IO?

[stephentoub]

What is io_uring? Is it a new algorithm for IO?

https://en.wikipedia.org/wiki/Io_uring