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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.

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