Messages in this thread | | | Date | Tue, 15 Oct 2002 15:12:38 -0400 | From | Benjamin LaHaise <> | Subject | Re: [PATCH] async poll for 2.5 |
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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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