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SubjectRe: [PATCH] async poll for 2.5
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.

-ben
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