Messages in this thread | | | Date | Tue, 15 Oct 2002 12:31:12 -0700 (PDT) | From | Davide Libenzi <> | Subject | Re: [PATCH] async poll for 2.5 |
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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
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