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Date: Tue, 27 Sep 2011 09:19:33 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH] Use qemu_eventfd for POSIX AIO
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To: Avi Kivity <avi@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, Jan Kiszka <jan.kiszka@siemens.com>, Marcelo Tosatti <mtosatti@redhat.com>, qemu-devel <qemu-devel@nongnu.org>

On 09/27/2011 09:11 AM, Avi Kivity wrote:
> On 09/27/2011 05:07 PM, Anthony Liguori wrote:
>>
>> You don't expect to handle EAGAIN with eventfd() whereas you have to handle it
>> with pipe().
>>
>> 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().
>
> We could define a qemu_event mechanism that satisfies the least common
> denominator, and is implemented by eventfd when available.
>
> qemu_event_create()
> qemu_event_signal()
> qemu_event_wait()
> qemu_event_poll_add() // registers in main loop
> qemu_event_poll_del()

See hw/event_notifier.[ch].

Regards,

Anthony Liguori

>