Re: [Qemu-devel] [PATCH] aio-posix: Fix return value of aio_poll()

[Paolo Bonzini]

Il 23/01/2013 09:58, Dietmar Maurer ha scritto:
>>>>> Are you using timers in any way?
>>>>
>>>> Yes, I call co_sleep_ns(rt_clock, delay) to limit rate to output
>>>> stream.
>>>
>>> Use block_job_sleep_ns instead, and only call it when no I/O is pending.
>>
>> Thanks, that works!
> 
> I currently use qemu_aio_set_fd_handler() to implement async output to
> the backup stream. While that works, performance is much better (during 
> backup)
> if I use a separate thread to write the data.
> 
> Is that known behavior, or should aio give about the same performance as 
> using a thread?

It depends, but this is what we saw for migration too.  You may also
have less contention on the big QEMU lock if you use a thread.

> Or would I get better performance if I use Linux native AIO support?

That also depends, but in general it should be faster.

Paolo