Re: [PATCH] qemu-kvm: Switch POSIX compat AIO implementation to upstream

[Avi Kivity <avi@redhat.com>]

On 09/26/2011 09:09 PM, Anthony Liguori wrote:
> On 09/26/2011 12:24 PM, Avi Kivity wrote:
>> On 09/26/2011 08:23 PM, Jan Kiszka wrote:
>>> >
>>> > Perhaps qemu_eventfd() can be used in the future instead of an 
>>> explicit
>>> > pipe. Then Linux will do eventfd while other OSes will fall back to
>>> > pipes.
>>>
>>> Basically simpler code, or does this also have runtime benefits?
>>>
>>
>> In corner cases, the completion can block on the write() with pipes, 
>> but not
>> eventfd.
>
> The pipe is O_NONBLOCK and the only thing the caller cares about is 
> whether there is *some* data in the PIPE so it can happily ignore EAGAIN.
>
> So the pipe implementation never blocks on write() either.  It may 
> require multiple reads to drain the queue though whereas eventfd would 
> only require a single read to drain the queue.
>

Oh, so switching to eventfd won't change much.  Still nice though IMO.

-- 
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