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SubjectRe: [patch 13/13] signalfd/timerfd/asyncfd v5 - KAIO asyncfd support (example/maybe-broken) ...
On Wed, 14 Mar 2007, Benjamin LaHaise wrote:

> On Wed, Mar 14, 2007 at 04:41:58PM -0700, Davide Libenzi wrote:
> > Yeah, of course. I do not plan revolutions. Just asking if it's a possible
> > thing to do. I can mlock the userspace ring, if imposing that burden over
> > aio_complete() is seen as too heavy.
>
> I'm not sure I follow what you're doing -- why isn't asyncfd merely calling
> io_getevents() instead of reinventing everything the ringbuffer does? The
> aio ringbuffer is already locked in memory. Fwiw, the aio ringbuffer was
> originally wired up to a file descriptor, but that gave way to the actual
> syscall in order to enforce proper typechecking and typical usage scenarios
> with timeouts.

The purpose of asyncfd is to provide a pollable (by the mean of
f_op->poll) device that can be hosted inside a standard select/poll/epoll
wait subsystem, and that, at the same time, provide a zero-copy way for
kernel code (KAIO and syslets/threadlets were my thought) to deliver
results to userspace.



> Also, there have been patches floating around for aio_poll and a way to get
> epoll wakeups into the aio event queue. They deserve serious consideration
> if this asyncfd seems necessary.

I don't want to talk about the AIO poll code, because last time I saw it,
it did not look shiny.
But I think we can agree that ppl needs to have a way to wait for both
block I/O (covered by either KAIO or syslets/threadlets) and all the other
world (covered by epoll). This has been pretty clear for me, looking at
the continuous request I got to provide block I/O completions through
epoll, and looking at the hackage that ppl has currently to do in
userspace to achieve that.
Now that I'm seeing I can wait for both block and net I/O, I got excited ;)



- Davide


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