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Questions tagged [io-uring]

37 questions
55
votes
4 answers

Is there really no asynchronous block I/O on Linux?

Consider an application that is CPU bound, but also has high-performance I/O requirements. I'm comparing Linux file I/O to Windows, and I can't see how epoll will help a Linux program at all. The kernel will tell me that the file descriptor is…
Jon Watte
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27
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1 answer

What exactly is io_uring?

Recently I've been seeing this in different forums. As far as I can tell from reading some forum discussions it is something to do with input and output. What exactly is io_uring?
Amani
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14
votes
1 answer

Why is liburing write performance lower than expected?

Problem Summary I am working on a project that requires streaming data to disk at very high speeds on a single Linux server. An fio benchmark using the command below shows that I should be able to get the desired write speeds (> 40 GB/s) using…
Smitch
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11
votes
2 answers

Comparing Boost.Asio, libunifex, liburing, and CppCoro

I am trying to understand asynchronous models in C++. I am investigating 4 libraries that purport to deal with asynchronous I/O: liburing (C version, C++ version): provides an interface for io_uring. The C++ version uses coroutines. libunifex:…
Mark Wallace
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4
votes
1 answer

Trouble compiling io_uring

I have been reading https://kernel.dk/io_uring.pdf and I would like to experiment with the actual syscalls (io_uring_setup, io_uring_enter) to check my understanding, but I am not able to compile the following simple program: #include…
sc46
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2
votes
1 answer

io_uring in multithreaded process

I am trying to write a multithreaded server using io_uring. The problem is the function 'io_uring_wait_cqe' requires calling to io_uring_cqe_seen to mark the CQE as seen. Therefore, in several threads, there may be a situation where the same event…
Rachel91
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2
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1 answer

Convert `ioctl` call in golang

I'm trying to convert, or at least understand this ioctl call: #define NVME_URING_CMD_IO _IOWR('N', 0x80, struct nvme_uring_cmd) Is there an equivalent of _IOWR in golang? maybe with the unix package?
Mascarpone
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2
votes
1 answer

How to create a single SQPOLL thread in io_uring for multiple rings (IORING_SETUP_SQPOLL)

Is it possible to create a single SQPOLL (iou-sqp) thread that polls submit requests of multiple io_uring rings? This questions comes from the desire to use multiple io_uring rings without making syscalls (entering kernel) when submitting I/O…
Yury
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2
votes
1 answer

io_uring_queue_init permission denied

I've updated my fedora linux with dnf update to kernel version Linux 5.16.7-200.fc35.x86_64 x86_64 and am now getting a EPERM/permission denied error for a call to io_uring_queue_init, even when calling my program as root. I am at a total loss, is…
Klemens Morgenstern
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2
votes
1 answer

Waiting for epoll and io_uring simultaneously

I'm migrating my project to io_uring for better performance. However, some part of the system depends on epoll being event system and not movable to io_uring (ex: database drivers, they write to socket internally and I get notification read/write…
Mary Chang
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2
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1 answer

Where is the function: trace_io_uring_submit_sqe in Linux kernel?

Recently, I'm tracing the io_uring in Linux kernel. I found a function trace_io_uring_submit_sqe was called in io_uring.c. Through searching symbol on Github mirror repository or on elixir.bootlin, I can't found the definition of its. Are there any…
Steven
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2
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0 answers

Why can't gdb read io_uring_cqe contents?

I am trying out loti-examples (Lord of the Uring) commit 8724d47 and liburing commit 7ff4fee on Ubuntu 20.04 with mainline kernel 5.12. I use the following patch for loti-examples to have a better debugging experience: diff --git a/CMakeLists.txt…
Janus Troelsen
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1
vote
0 answers

IoUring with batch submission decrease the throughput

I want to use IoUring to speed up my application. After some search, I found that batch-submit IO requests can have higher throughput. Therefore, I write the following code to read a big file(3.6GB): let mut file =…
YjyJeff
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1
vote
1 answer

Read at position relative to end of the file via IoUring

How can I read at the position relative to end of the file via IoUring? I have a file that contains the metadata in the end of the file because of single pass writing. Now, I want to read the file via IoUring for efficiency, therefore I have to read…
YjyJeff
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1
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1 answer

liburing: io_uring_submit() causes error when placed in await_suspend

I'm currently trying out C++ coroutines abstracting away io_uring. For that I have the following class: class io_service final { public: explicit io_service(unsigned size, threadpool& pool) : pool_(pool) { if (auto ret =…
Frederic Schönberger
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