探索性能巅峰：io_uring用户态接口的神奇之处-阿里云开发者社区

一、io_uring和epoll的区别

（1）epoll设置事件完成之后，以后只要不修改或删除事件，就可以一直等待IO事件触发。即事件驱动机制。

epoll对事件的管理使用的是红黑树。

（2）io_uring有两个队列，SQ和CQ，io_uring_submite之后，事件提交在SQ等待，事件达到后交给CQ，应用程序调用io_uring_peek_batch_cqe从CQ取出后，会调用io_uring_cq_advance将事件触发销毁，因此要想一直可以等待事件，需要从CQ取出后再次把事件加入SQ中。即异步机制。

io_uring对事件的管理采用两个队列：SQ（submition queue）和CQ（completion queue）。

二、io_uring 与epoll性能比较

2.1、安装rust_echo_bench测试工具

（1）安装cargo：

# ubuntusudo apt-get install cargo
# centossudo yum install cargo

（2）下载rust_echo_bench：

git clone https://github.com/haraldh/rust_echo_bench.git

（3）编译rust_echo_bench：

cd rust_echo_bench
cargo run --release----help

执行过程：

Updating crates.io index
  Downloaded unicode-width v0.1.9
  Downloaded getopts v0.2.21
  Downloaded 2 crates (35.2 KB) in1.58s
   Compiling unicode-width v0.1.9
   Compiling getopts v0.2.21
   Compiling echo_bench v0.2.0 (/home/user/rust_echo_bench)
    Finished release [optimized] target(s) in 4m 05s
     Running `target/release/echo_bench --help`Echo benchmark.
Usage:
  target/release/echo_bench [ -a <address> ] [ -l <length> ] [ -c <number> ] [ -t <duration> ]
  target/release/echo_bench (-h | --help)
  target/release/echo_bench --versionOptions:
-h, --help          Print this help.
-a, --address <address>
                        Target echo server address. Default: 127.0.0.1:12345
-l, --length <length>
                        Test message length. Default: 512-t, --duration <duration>
                        Test duration in seconds. Default: 60-c, --number <number>
                        Test connection number. Default: 50

（3）运行

cargo run --release----address"192.168.7.233:9999"--number1000--duration60--length512

将相关参数修改即可。

2.2、测试比较

io_uring结果：

Finished release [optimized] target(s) in0.00s
     Running `target/release/echo_bench --address '192.168.7.233:9999' --number 1000 --duration 60 --length 512`Benchmarking: 192.168.7.235:9999
1000 clients, running 512 bytes, 60 sec.
Speed: 8836 request/sec, 8836 response/sec
Requests: 530176Responses: 530176

epoll测试前，需要先调整ulimit大小：ulimit -n 1024567。

epoll结果：

Finished release [optimized] target(s) in0.01s
     Running `target/release/echo_bench --address '192.168.7.233:8888' --number 1000 --duration 60 --length 512`Benchmarking: 192.168.7.233:8888
1000 clients, running 512 bytes, 60 sec.
Speed: 7908 request/sec, 7908 response/sec
Requests: 474517Responses: 474516

注意，此测试结果仅仅是某次数据或访问的比较，为自己编写的代码提供一种测试方案，不作为说明io_uring与epoll/poll/select的性能高低。

2.3、小结

io_uring在性能上不比reactor高多少，io_uring不一定会完全替代epoll，未来是io_uring与epoll并存，只是网络IO事件的处理方案多了一个选择。

三、实现封装io_uring用户态文件读写接口

io_uring提供三个系统调用接口：io_uring_submit()、io_uring_enter()、io_uring_register()。不使用liburing情况下，需要自己实现用户层的接口。io_uring除了可以处理网络IO，也可以处理磁盘IO事件。

3.1、系统调用

系统调用函数是syscall。调用syscall函数时，会触发一个0x80的中断。每个系统调用都有系统调用号，存放在sys_call_table数组中。

流程：调用syscall，触发0x80中断，将系统调用号赋给eax寄存器，参数赋给ebx、ecx等寄存器，然后执行system_call。

函数原型：

#define _GNU_SOURCE         /* See feature_test_macros(7) */#include <unistd.h>#include <sys/syscall.h>   /* For SYS_xxx definitions */longsyscall(longnumber, ...);

使用示例：

#define _GNU_SOURCE#include <unistd.h>#include <sys/syscall.h>#include <sys/types.h>#include <signal.h>intmain(intargc, char*argv[])
{
pid_ttid;
tid=syscall(SYS_gettid);
tid=syscall(SYS_tgkill, getpid(), tid, SIGHUP);
}

3.2、内存映射mmap

应用层和内核直接数据交互，可以通过映射内存块的方式。

函数原型：

#include <sys/mman.h>void*mmap(void*addr, size_tlength, intprot, intflags,
intfd, off_toffset);
intmunmap(void*addr, size_tlength);

使用示例：

#include <sys/mman.h>#include <sys/stat.h>#include <fcntl.h>#include <stdio.h>#include <stdlib.h>#include <unistd.h>#define handle_error(msg) \do { perror(msg); exit(EXIT_FAILURE); } while (0)intmain(intargc, char*argv[])
{
char*addr;
intfd;
structstatsb;
off_toffset, pa_offset;
size_tlength;
ssize_ts;
if (argc<3||argc>4) {
fprintf(stderr, "%s file offset [length]\n", argv[0]);
exit(EXIT_FAILURE);
    }
fd=open(argv[1], O_RDONLY);
if (fd==-1)
handle_error("open");
if (fstat(fd, &sb) ==-1)           /* To obtain file size */handle_error("fstat");
offset=atoi(argv[2]);
pa_offset=offset&~(sysconf(_SC_PAGE_SIZE) -1);
/* offset for mmap() must be page aligned */if (offset>=sb.st_size) {
fprintf(stderr, "offset is past end of file\n");
exit(EXIT_FAILURE);
    }
if (argc==4) {
length=atoi(argv[3]);
if (offset+length>sb.st_size)
length=sb.st_size-offset;
/* Can't display bytes past end of file */    } else {    /* No length arg ==> display to end of file */length=sb.st_size-offset;
    }
addr=mmap(NULL, length+offset-pa_offset, PROT_READ,
MAP_PRIVATE, fd, pa_offset);
if (addr==MAP_FAILED)
handle_error("mmap");
s=write(STDOUT_FILENO, addr+offset-pa_offset, length);
if (s!=length) {
if (s==-1)
handle_error("write");
fprintf(stderr, "partial write");
exit(EXIT_FAILURE);
    }
exit(EXIT_SUCCESS);
}

3.3、SQ_RING、CQ_RING、SQES关系

SQ_RING和CQ_RING的各项偏移指向SQES，真正存储数据的是SQES。

3.4、代码实现示例

#include <stdio.h>#include <stdlib.h>#include <sys/stat.h>#include <sys/ioctl.h>#include <sys/syscall.h>#include <sys/mman.h>#include <sys/uio.h>#include <linux/fs.h>#include <fcntl.h>#include <unistd.h>#include <string.h>#include <linux/io_uring.h>#define URING_QUEUE_DEPTH   1024#define BLOCK_SZ            1024// 定义结构体，将内核数据mmap到用户层structapp_io_sq_ring {
unsigned*head;
unsigned*tail;
unsigned*ring_mask;
unsigned*ring_entries;
unsigned*flags;
unsigned*array;
};
structapp_io_cq_ring {
unsigned*head;
unsigned*tail;
unsigned*ring_mask;
unsigned*ring_entries;
structio_uring_cqe*cqes;
};
// 返回structsubmitter {
intring_fd;
structapp_io_sq_ringsq_ring;
structapp_io_cq_ringcq_ring;
structio_uring_sqe*sqes;
};
// file infostructfile_info {
off_tfile_sz;
structioveciovecs[];
};
intio_uring_setup(unsignedentries, structio_uring_params*p)
{
// io_uring.c// SYSCALL_DEFINE2(io_uring_setup,u32,entries,struct io_uring_params __user *,params)// 内核代码 io_uring_setupreturn (int)syscall(__NR_io_uring_setup, entries, p);
}
intio_uring_enter(intring_fd, unsignedintto_submit,
unsignedintmin_complete, unsignedintflags)
{
return (int)syscall(__NR_io_uring_enter, ring_fd, to_submit, min_complete, flags, NULL, 0);
}
intapp_setup_uring(structsubmitter*s)
{
structio_uring_paramsp;
memset(&p, 0, sizeof(p));
// 创建 CQ和SQ 内存空间s->ring_fd=io_uring_setup(URING_QUEUE_DEPTH, &p);
if (s->ring_fd<0)
return-1;
intsring_sz=p.sq_off.array+p.sq_entries*sizeof(unsigned);
intcring_sz=p.cq_off.cqes+p.cq_entries*sizeof(structio_uring_cqe);
// 单映射，判断cq和sq是否公用一块内存if (p.features&IORING_FEAT_SINGLE_MMAP)
    {
if (cring_sz>sring_sz)
sring_sz=cring_sz;
cring_sz=sring_sz;
    }
// mmap sq空间void*sq_ptr=mmap(0, sring_sz, PROT_READ|PROT_WRITE,
MAP_SHARED|MAP_POPULATE, s->ring_fd, IORING_OFF_SQ_RING);
if (sq_ptr==MAP_FAILED)
return-1;
// 单映射，判断cq和sq是否公用一块内存void*cq_ptr=NULL;
if (p.features&IORING_FEAT_SINGLE_MMAP)
    {
cq_ptr=sq_ptr;
    }
else    {
// mmap cq空间cq_ptr=mmap(0, sring_sz, PROT_READ|PROT_WRITE,
MAP_SHARED|MAP_POPULATE, s->ring_fd, IORING_OFF_CQ_RING);
if (cq_ptr==MAP_FAILED)
return-1;
    }
structapp_io_sq_ring*sring=&s->sq_ring;
structapp_io_cq_ring*cring=&s->cq_ring;
// sq赋值sring->head=sq_ptr+p.sq_off.head;
sring->tail=sq_ptr+p.sq_off.tail;
sring->ring_mask=sq_ptr+p.sq_off.ring_mask;
sring->ring_entries=sq_ptr+p.sq_off.ring_entries;
sring->flags=sq_ptr+p.sq_off.flags;
sring->array=sq_ptr+p.sq_off.array;
// 将sqes映射到用户空间s->sqes=mmap(0, p.sq_entries*sizeof(structio_uring_sqe),PROT_READ|PROT_WRITE,
MAP_SHARED|MAP_POPULATE, s->ring_fd, IORING_OFF_SQES);
if (s->sqes==MAP_FAILED)
return-1;
// cq赋值cring->head=cq_ptr+p.cq_off.head;
cring->tail=cq_ptr+p.cq_off.tail;
cring->ring_mask=cq_ptr+p.cq_off.ring_mask;
cring->ring_entries=cq_ptr+p.cq_off.ring_entries;
cring->cqes=sq_ptr+p.cq_off.cqes;
return0;
}
// get file sizeoff_tget_file_size(intfd)
{
structstatst;
if (fstat(fd, &st) <0)
return-1;
if (S_ISBLK(st.st_mode))
    {
unsignedlonglongbytes;
if (ioctl(fd, BLKGETSIZE64, &bytes) !=0)
return-1;
returnbytes;
    }
elseif (S_ISREG(st.st_mode))
returnst.st_size;
return-1;
}
voidoutput_to_console(char*buf,intlen)
{
while (len--)
    {
fputc(*buf++, stdout);
    }
}
voidread_from_cq(structsubmitter*s)
{
structfile_info*fi;
structapp_io_cq_ring*cring=&s->cq_ring;
structio_uring_cqe*cqe;
unsignedhead=*cring->head;
while (1)
    {
if (head==*cring->tail)
break;
cqe=&cring->cqes[head&*s->cq_ring.ring_mask];
fi= (structfile_info*)cqe->user_data;
if (cqe->res<0)
fprintf(stderr, "error: %d\n", cqe->res);
intblocks=fi->file_sz/BLOCK_SZ;
if (fi->file_sz%BLOCK_SZ)
blocks++;
inti=0;
while (++i<blocks)
        {
output_to_console(fi->iovecs[i].iov_base, fi->iovecs[i].iov_len);
printf("################################ i : %d, blocks : %d\n",i, blocks);
        }
head++;
printf("head : %d,tail : %d, blocks: %d\n", head, *cring->tail,blocks);
    }
*cring->head=head;
printf("read form cq end!\n");
}
intsubmit_to_sq(char*file_path,structsubmitter*s)
{
intfilefd=open(file_path, O_RDONLY);
if (filefd<0)
return-1;
off_tfilesz=get_file_size(filefd);
if (filesz<0) {
close(filefd);
return-1;
    }
structapp_io_sq_ring*sring=&s->sq_ring;
off_tbytes_remaining=filesz;
intblocks=filesz/BLOCK_SZ;
if (filesz%BLOCK_SZ)
blocks++;
structfile_info*fi=malloc(sizeof(structfile_info) +sizeof(structiovec)*blocks);
if (!fi)
    {
close(filefd);
return-2;
    }
fi->file_sz=filesz;
unsignedcurrent_block=0;
while (bytes_remaining)
    {
off_tbytes_to_read=bytes_remaining;
if (bytes_to_read>BLOCK_SZ)
bytes_to_read=BLOCK_SZ;
fi->iovecs[current_block].iov_len=bytes_to_read;
void*buf;
if (posix_memalign(&buf, BLOCK_SZ, BLOCK_SZ))
        {
close(filefd);
return1;
        }
fi->iovecs[current_block].iov_base=buf;
current_block++;
bytes_remaining-=bytes_to_read;
    }
unsignednext_tail=0, tail=0, index=0;
next_tail=tail=*sring->tail;
next_tail++;
index=tail&*s->sq_ring.ring_mask;
structio_uring_sqe*sqe=&s->sqes[index];
sqe->fd=filefd;
sqe->flags=0;
sqe->opcode=IORING_OP_READV;
sqe->addr= (unsignedlong)fi->iovecs;
sqe->len=blocks;
sqe->off=0;
sqe->user_data= (unsignedlonglong)fi;
sring->array[index] =index;
tail=next_tail;
if (*sring->tail!=tail)
*sring->tail=tail;
intret=io_uring_enter(s->ring_fd, 1, 1, IORING_ENTER_GETEVENTS);
if (ret<0)
    {
close(filefd);
return-1;
    }
close(filefd);
return0;
}
intmain(intargc, char*argv[])
{
structsubmitter*s=malloc(sizeof(structsubmitter));
if (s==NULL)
    {
perror("malloc fail");
return-1;
    }
memset(s, 0, sizeof(structsubmitter));
if (app_setup_uring(s))
return1;
inti=1;
for (i=1; i<argc; i++)
    {
if (submit_to_sq(argv[i], s))
return1;
read_from_cq(s);
    }
return0;
}