Re: [Qemu-devel] RFC: x86_64 Best way to fix 'cast to pointer from integer of different size' problems?

[Stuart Anderson <anderson@netsweng.com>]

On Tue, 6 Nov 2007, Fabrice Bellard wrote:

> Paul Brook wrote:
>> [...]
>> Personally I like the locking interface as it allows a zero-copy
>> implementation. However the kernel uses a copying interface, and my
>> understanding is that other qemu maintainers also prefer the copying
>> interface.
>
> At least I don't think it is critical performance wise, especially if
> the page flag checks are added ! Before you added the current zero copy
> interface, my plan was to use a zero copy interface just for big buffers
> such as the one for read/write.

By the time you consider the different combinations of targets & hosts,
most of the opportunities for zero copy are eliminated anyway. Byte
ordering and structure packing amd content differences mean that we can't
do zero-copy except in the rare circumstance that the host & target
match is all of these respects. The read & write buffers would still
benefit from zero copy, but nearly everything else has to be touched
anyway.


                                 Stuart

Stuart R. Anderson                               anderson@netsweng.com
Network & Software Engineering                   http://www.netsweng.com/
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