Epoll introduction

Multiple client connections arrive kernel（ kernel ）

Threads / process read fd  Read the kernel

BIO：socket stay   This period is blocking （ Multi process ）

NIO： Synchronous non blocking period （ But the process ）

Multiplexing NIO：kernel Added in select 

NIO： If there is 1000fd Call on behalf of user process rotation 1000 Time kernel, It costs a lot

Multiplexing NIO：kernel Added in select , Kernel first select（1000fds）, Return useful , Process re read（fd）

User mode 、 Kernel mode  

Kernel area , Users cannot access , So we need to transfer data , Lead to fd Relevant data are copied around

How to improve ： Spaces （ Red and black trees 、 Linked list 、mmap） Part of the kernel , Also part of the user

In the process, the file descriptor is placed in the red black tree , Put the data into the linked list

Zero copy ：kernel More than one sendfile（ system call ）（out,in） 、read（fd）、write（fd）

Network card to kernel socketIO 

File to kernel file IO

sendfile： Progress tune sendfile The kernel reads data and gets it to the buffer , Send it directly