Re: Efficient Event Handling In Linux?

[jury gerold <geroldj@grips.com>]

I want to add, that the SGI kaio patch handles disk as well as sockets.

Gerold

Dan Kegel wrote:

>"David E. Weekly" <dweekly@legato.com> wrote:
>
>>Hey all. I've been looking at efficient event-handling mechanisms (for I/O
>>on sockets, disk, devices) ... As far as I could tell ... the discussion 
>>[on linux-kernel] trailed off without any real resolution as to what
>>would actually be done to empower Linux with efficient event handling;
>>perhaps I missed it, but I couldn't find Linus's get_events/bind_event
>>calls, nor could I find /dev/poll or kqueue-styled interfaces integrated
>>into the latest kernel.
>>I did find what looks to be an excellent patch in the way of /dev/epoll
>>(written up here:
>>http://www.xmailserver.org/linux-patches/nio-improve.html). According to the
>>benchmarks he's got, the patch really spanks /dev/poll and POSIX SIGIO. I'm
>>going to begin testing with it soon and was hoping to get some feel for
>>whether /dev/epoll might end up in the kernel mainstream at some point in
>>the not-too-distant future? 
>>
>
>My impression is that /dev/epoll is the best for sockets at the moment, and 
>that several people are using it happily now.  (The interface is
>still in flux, I think, so only use it now if you don't mind that.)
>
>However, for disk I/O, IMHO you really want aio instead.
>If you need aio now, SGI's kaio patch is available and is said to work well 
>(and heck, there's also a userland emulation in glibc, but I 
>suspect it doesn't perform well).
>For the future, Ben LaHaise's aio may have better performance when it's done
>( http://uwsg.iu.edu/hypermail/linux/kernel/0102.0/0459.html );
>he's going to do things like async sendfile, and is willing to provide a nonposix
>interface for those who don't want signal delivery's overhead
>(see http://uwsg.iu.edu/hypermail/linux/kernel/0102.0/0384.html
>and http://www.kvack.org/~blah/aio/v2.4.5-ac9-bcrl4-aio.diff )
>
>I suspect both /dev/epoll and LaHaise's aio will end up being integrated 
>into the stock 2.5 kernel.  And if we're really lucky, there will be 
>a single integrated event stream for both.  I'm quite annoyed
>that Posix defines separate polling methods for file descriptors
>and aio completions (http://www.opengroup.org/onlinepubs/7908799/xsh/aio_suspend.html);
>if one simple interface can handle both, we ought to try to do it.
>
>- Dan "but I play one on TV" Kegel
>