linux – io_submit和带有O_ASYNC的文件有什么区别

根据本教程,有两种不同的异步IO模型：

>异步阻塞I / O：使用O_ASYNC打开文件,然后使用epoll / poll / select.
>异步IO：在该文章中使用glibc AIO.因为glibc实现只是通过线程池的模拟,我在这个问题中提到的是kernel AIO,即io_submit.

至少从概念的角度来看,没有什么大不同,真的,io_submit可以让你发出多个io reqeusts,另一方面,使用带有O_ASYNC的read,你可以发出一个带有隐含文件位置的请求.

而guide也提到使用epoll替代Linux AIO：

epoll. Linux has limited support for using epoll as a mechanism for
asynchronous I/O. For reads to a file opened in buffered mode (that
is,without O_DIRECT),if the file is opened as O_NONBLOCK,then a
read will return EAGAIN until the relevant part is in memory. Writes
to a buffered file are usually immediate,as they are written out with
another writeback thread. However,these mechanisms don’t give the
level of control over I/O that direct I/O gives.

使用epoll作为AIO替代品有什么问题？或者换句话说,我们需要一个新的接口io_submit来解决的问题是什么？