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Re: [Qemu-devel] 4G address space remapping on 64-bit host

From: Fabrice Bellard
Subject: Re: [Qemu-devel] 4G address space remapping on 64-bit host
Date: Fri, 29 Jun 2007 12:15:25 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20050922 Fedora/1.7.12-1.3.1


In fact, running in 64 bit is not necessary : It is simpler and more efficient to use kqemu (or KVM) to handle the address space remapping. The trick is to run the translator in the upper part or lower part of the 32 bit address space and to protect it with segments.

Even in 64 bit mode, using kqemu would be more efficient because it could handle scattered address spaces more efficiently than the host OS.


Blue Swirl wrote:

I had an idea of mapping the full 32-bit target virtual address space
to a 4GB area on 64-bit hosts. Then the loads and stores to normal RAM
(except page tables, code_mem_write etc) could be made much faster,
falling back to softmmu for other pages. The idea has come up before,
for example in this Fabrice's message:

But I'm not sure if this would be worth the effort, the speedup would
depend on the frequency of the loads/stores and also translation time
vs. translated code execution times. Does anyone have good statistics
on those?

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