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Re: [Qemu-devel] RFC: x86_64 Best way to fix 'cast to pointer from integ


From: Paul Brook
Subject: Re: [Qemu-devel] RFC: x86_64 Best way to fix 'cast to pointer from integer of different size' problems?
Date: Tue, 6 Nov 2007 22:05:34 +0000
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> 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.

If you're not careful you get double-copying. Once copying the struct from 
guest to host space, and then again when converting layout/endianess.

I've no idea whether this overhead is important in practice though.

Paul




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