Re: [PATCH] async poll for 2.5

[Davide Libenzi]

On Tue, 15 Oct 2002, Benjamin LaHaise wrote:

> On Tue, Oct 15, 2002 at 12:16:39PM -0700, Davide Libenzi wrote:
> > Ben, one of the reasons of the /dev/epoll speed is how it returns events
> > and how it collapses them. A memory mapped array is divided by two and
> > while the user consumes events in one set, the kernel fill the other one.
> > The next wait() will switch the pointers. There is no copy from kernel to
> > user space. Doing :
> >
> > int sys_epoll_wait(int epd, struct pollfd **pevts, int timeout);
> >
> > the only data the kernel has to copy to userspace is the 4(8) bytes for
> > the "pevts" pointer.
>
> Erm, the aio interface has support for the event ringbuffer being accessed
> by userspace (it lives in user memory and the kernel acts as a writer, with
> userspace as a reader), that's one of its advantages -- completion events
> are directly accessible from userspace after being written to by an
> interrupt.  Ideally this is to be wrapped in a vsyscall, but we don't have
> support for that yet on x86, although much of the code written for x86-64
> should be reusable.

In general I would like to have a "common" interface to retrieve IO
events, but IMHO the two solutions should be benchmarked before adopting
the one or the other.

- Davide