Re: [ANNOUNCE] kvm-14 release

Avi Kivity
2007-02-22T17:29:49Z

Anthony Liguori wrote:
> Avi Kivity wrote:
>> Laurent Vivier wrote:
>>> There are remaining issues : libposix-aio uses kernel AIO, so files
>>> must be
>>> opened using O_DIRECT and buffers must be aligned. libposix-aio is
>>> able to
>>> manage other cases but this has a performance cost.
>>>
>>>
>>
>> Because the guest is also doing dma, the buffers are expected to be
>> aligned (it might be different if using pio, but unlikely).
>
> The IDE emulation always uses a temporary buffer. This is partially
> because you cannot always rely on being able to use an offset on
> phys_ram_base (when doing user only emulation).

Why is that?

>
> We can pretty easily patch this code though to use the DMA address
> directly instead of the temporary buffer in the non PIO case. We
> still have to define a raw_pread() that is capable of emulating sector
> alignment though since Linux will use PIO at first.

Sure. It seems worthwhile for mainline qemu too.

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