Re: [Qemu-devel] [PATCH] Use qemu_eventfd for POSIX AIO

[Avi Kivity]

On 09/27/2011 05:36 PM, Jan Kiszka wrote:
> On 2011-09-27 16:34, Avi Kivity wrote:
> >  On 09/27/2011 05:29 PM, Jan Kiszka wrote:
> >>>
> >>>   Moreover, the eventfd() counter is not lossy (practically speaking) 
> whereas if
> >>>   you use pipe() as a counter, it will be lossy in practice.
> >>>
> >>>   This is why posix aio uses pipe() and not eventfd().
> >>
> >>  I don't get this yet. eventfd is lossy by default. It only decreases the
> >>  counter on read if you specify EFD_SEMAPHORE - which we do not do.
> >>
> >
> >  It's not lossy - a read returns the number of events written since the
> >  last read.
>
> Yeah, but what's the point? We don't evaluate this.

If we write an interface that looks like eventfd but subtly differs, 
someone will get bitten.  If we write a new interface and implement it 
via eventfd (or a pipe), no one gets bitten.

--
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