iouring 基础

整体印象

io_uring 有如此出众的性能，主要来源于以下几个方面：

用户态和内核态共享提交队列（submission queue）和完成队列（completion queue）

IO 提交和收割可以 offload 给 Kernel，且提交和完成不需要经过系统调用（system call）

支持 Block 层的 Polling 模式

通过提前注册用户态内存地址，减少地址映射的开销

不仅如此，io_uring 还可以完美支持 buffered IO，而 libaio 对于 buffered IO 的支持则一直是被诟病的地方。

io uring 可以使用的位置

替代 aio
network
- https://developer.aliyun.com/article/834974
epoll
async submit syscall
替代 dpdk / spdk :

基本 API 使用

推荐 : https://nick-black.com/dankwiki/index.php/Io_uring

这里里面的东西全部都需要背下来吧

io uring 一共支持哪些系统调用

一共就是三个:

int io_uring_setup(u32 entries, struct io_uring_params *p);
int io_uring_register(unsigned fd, unsigned opcode, void *arg, unsigned int nr_args);
int io_uring_enter(unsigned fd, u32 to_submit, u32 min_complete, u32 flags, const void* argp, size_t argsz);

所以，当运行起来的时候，只会去调用 io_uring_enter 的

liburing 提供的两个接口都是回去调用 io_uring_enter :

io_uring_submit
io_uring_wait_cqe : 不需要复杂的设置就可以避免系统调用，如果他发现已经存在完成的任务，那么可以直接返回。

io_uring_enter 参数 flags 的含义

https://manpages.debian.org/unstable/liburing-dev/io_uring_enter.2.en.html

/*
 * io_uring_enter(2) flags
 */
#define IORING_ENTER_GETEVENTS		(1U << 0)
#define IORING_ENTER_SQ_WAKEUP		(1U << 1)
#define IORING_ENTER_SQ_WAIT		(1U << 2)
#define IORING_ENTER_EXT_ARG		(1U << 3)
#define IORING_ENTER_REGISTERED_RING	(1U << 4)
#define IORING_ENTER_ABS_TIMER		(1U << 5)
#define IORING_ENTER_EXT_ARG_REG	(1U << 6)
#define IORING_ENTER_NO_IOWAIT		(1U << 7)

IORING_ENTER_GETEVENTS : Wait until at least min_complete CQEs are ready before returning.
IORING_ENTER_SQ_WAKEUP : Wake up the kernel thread created when using IORING_SETUP_SQPOLL.
IORING_ENTER_SQ_WAIT : Wait until at least one entry is free in the submission ring before returning.
IORING_ENTER_EXT_ARG : (Since Linux 5.11) Interpret sig to be a io_uring_getevents_arg rather than a pointer to sigset_t. This structure can specify both a sigset_t and a timeout.
IORING_ENTER_REGISTERED_RING : ring_fd is an offset into the registered ring pool rather than a normal file descriptor.
IORING_ENTER_ABS_TIMER : (Since Linux 6.12) The timeout argument in the io_uring_getevents_arg is an absolute time, using the registered clock.

io_uring_setup(2)

https://man7.org/linux/man-pages/man2/io_uring_setup.2.html

io_uring_register(2) 支持的功能

主要是这几类:

Ring : IORING_REGISTER_RING_FDS (不能理解!)
Buffers : 固定 buffer I/O（高性能）
File descriptors : 内核无需每次通过 fdtable 查找 file 结构，提升性能。
- 但是通过 fd 查询找到文件的过程比较很低效的

https://man7.org/linux/man-pages/man2/io_uring_register.2.html 完整结果如下:

/*
 * io_uring_register(2) opcodes and arguments
 */
enum io_uring_register_op {
	IORING_REGISTER_BUFFERS			= 0,
	IORING_UNREGISTER_BUFFERS		= 1,
	IORING_REGISTER_FILES			= 2,
	IORING_UNREGISTER_FILES			= 3,
	IORING_REGISTER_EVENTFD			= 4,
	IORING_UNREGISTER_EVENTFD		= 5,
	IORING_REGISTER_FILES_UPDATE		= 6,
	IORING_REGISTER_EVENTFD_ASYNC		= 7,
	IORING_REGISTER_PROBE			= 8,
	IORING_REGISTER_PERSONALITY		= 9,
	IORING_UNREGISTER_PERSONALITY		= 10,
	IORING_REGISTER_RESTRICTIONS		= 11,
	IORING_REGISTER_ENABLE_RINGS		= 12,

	/* extended with tagging */
	IORING_REGISTER_FILES2			= 13,
	IORING_REGISTER_FILES_UPDATE2		= 14,
	IORING_REGISTER_BUFFERS2		= 15,
	IORING_REGISTER_BUFFERS_UPDATE		= 16,

	/* set/clear io-wq thread affinities */
	IORING_REGISTER_IOWQ_AFF		= 17,
	IORING_UNREGISTER_IOWQ_AFF		= 18,

	/* set/get max number of io-wq workers */
	IORING_REGISTER_IOWQ_MAX_WORKERS	= 19,

	/* register/unregister io_uring fd with the ring */
	IORING_REGISTER_RING_FDS		= 20,
	IORING_UNREGISTER_RING_FDS		= 21,

	/* register ring based provide buffer group */
	IORING_REGISTER_PBUF_RING		= 22,
	IORING_UNREGISTER_PBUF_RING		= 23,

	/* sync cancelation API */
	IORING_REGISTER_SYNC_CANCEL		= 24,

	/* register a range of fixed file slots for automatic slot allocation */
	IORING_REGISTER_FILE_ALLOC_RANGE	= 25,

	/* return status information for a buffer group */
	IORING_REGISTER_PBUF_STATUS		= 26,

	/* set/clear busy poll settings */
	IORING_REGISTER_NAPI			= 27,
	IORING_UNREGISTER_NAPI			= 28,

	IORING_REGISTER_CLOCK			= 29,

	/* clone registered buffers from source ring to current ring */
	IORING_REGISTER_CLONE_BUFFERS		= 30,

	/* send MSG_RING without having a ring */
	IORING_REGISTER_SEND_MSG_RING		= 31,

	/* register a netdev hw rx queue for zerocopy */
	IORING_REGISTER_ZCRX_IFQ		= 32,

	/* resize CQ ring */
	IORING_REGISTER_RESIZE_RINGS		= 33,

	IORING_REGISTER_MEM_REGION		= 34,

	/* this goes last */
	IORING_REGISTER_LAST,

	/* flag added to the opcode to use a registered ring fd */
	IORING_REGISTER_USE_REGISTERED_RING	= 1U << 31
};

sqe->flags 支持哪些

/*
 * sqe->flags
 */
/* use fixed fileset */
#define IOSQE_FIXED_FILE	(1U << IOSQE_FIXED_FILE_BIT)
/* issue after inflight IO */
#define IOSQE_IO_DRAIN		(1U << IOSQE_IO_DRAIN_BIT)
/* links next sqe */
#define IOSQE_IO_LINK		(1U << IOSQE_IO_LINK_BIT)
/* like LINK, but stronger */
#define IOSQE_IO_HARDLINK	(1U << IOSQE_IO_HARDLINK_BIT)
/* always go async */
#define IOSQE_ASYNC		(1U << IOSQE_ASYNC_BIT)
/* select buffer from sqe->buf_group */
#define IOSQE_BUFFER_SELECT	(1U << IOSQE_BUFFER_SELECT_BIT)
/* don't post CQE if request succeeded */
#define IOSQE_CQE_SKIP_SUCCESS	(1U << IOSQE_CQE_SKIP_SUCCESS_BIT)

ioring 函数 `__cold`

例如:

static __cold void io_tctx_exit_cb(struct callback_head *cb)

/*
 *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-cold-function-attribute
 *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html#index-cold-label-attribute
 *
 * When -falign-functions=N is in use, we must avoid the cold attribute as
 * contemporary versions of GCC drop the alignment for cold functions. Worse,
 * GCC can implicitly mark callees of cold functions as cold themselves, so
 * it's not sufficient to add __function_aligned here as that will not ensure
 * that callees are correctly aligned.
 *
 * See:
 *
 *   https://lore.kernel.org/lkml/Y77%2FqVgvaJidFpYt@FVFF77S0Q05N
 *   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88345#c9
 */
#if !defined(CONFIG_CC_IS_GCC) || (CONFIG_FUNCTION_ALIGNMENT == 0)
#define __cold				__attribute__((__cold__))
#else
#define __cold
#endif

文档： https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html

表示该函数执行概率很低。

io_wq_submit_work
- io_arm_poll_handler
  - __io_arm_poll_handler
io_poll_check_events

show_fdinfo

[root@nixos:/proc/118496/fdinfo]# cat 4
pos:    0
flags:  02000002
mnt_id: 14
ino:    240059
SqMask: 0x7f
SqHead: 3777186
SqTail: 3777186
CachedSqHead:   3777186
CqMask: 0x7f
CqHead: 3777060
CqTail: 3777091
CachedCqTail:   3777091
SQEs:   0
CQEs:   31
   36: user_data:0, res:4096, flag:0
   37: user_data:0, res:4096, flag:0
   38: user_data:0, res:4096, flag:0
   39: user_data:0, res:4096, flag:0
   40: user_data:0, res:4096, flag:0
   41: user_data:0, res:4096, flag:0
   42: user_data:0, res:4096, flag:0
   43: user_data:0, res:4096, flag:0
   44: user_data:0, res:4096, flag:0
   45: user_data:0, res:4096, flag:0
   46: user_data:0, res:4096, flag:0
   47: user_data:0, res:4096, flag:0
   48: user_data:0, res:4096, flag:0
   49: user_data:0, res:4096, flag:0
   50: user_data:0, res:4096, flag:0
   51: user_data:0, res:4096, flag:0
   52: user_data:0, res:4096, flag:0
   53: user_data:0, res:4096, flag:0
   54: user_data:0, res:4096, flag:0
   55: user_data:0, res:4096, flag:0
   56: user_data:0, res:4096, flag:0
   57: user_data:0, res:4096, flag:0
   58: user_data:0, res:4096, flag:0
   59: user_data:0, res:4096, flag:0
   60: user_data:0, res:4096, flag:0
   61: user_data:0, res:4096, flag:0
   62: user_data:0, res:4096, flag:0
   63: user_data:0, res:4096, flag:0
   64: user_data:0, res:4096, flag:0
   65: user_data:0, res:4096, flag:0
   66: user_data:0, res:4096, flag:0
SqThread:       -1
SqThreadCpu:    -1
UserFiles:      1
UserBufs:       128
PollList:
CqOverflowList:

iouring 基础

:book: Notes about Linux Kernel, Compiler and GPU

iouring 基础

整体印象

基本 API 使用

io uring 一共支持哪些系统调用

io_uring_enter 参数 flags 的含义

io_uring_setup(2)

io_uring_register(2) 支持的功能

sqe->flags 支持哪些

ioring 函数 `__cold`

show_fdinfo

Links

iouring 基础

整体印象

基本 API 使用

io uring 一共支持哪些系统调用

io_uring_enter 参数 flags 的含义

io_uring_setup(2)

io_uring_register(2) 支持的功能

sqe->flags 支持哪些

ioring 函数 __cold

show_fdinfo

Links

ioring 函数 `__cold`