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Re: [Qemu-devel] softmmu thoughts

From: Fabrice Bellard
Subject: Re: [Qemu-devel] softmmu thoughts
Date: Wed, 20 Oct 2004 14:41:42 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.2) Gecko/20040803


The idea is interesting. Here are several suggestions:

- It would be more efficient and simpler to map one 4KB host memory page every 8 KB. Then you can have a fixed mmap() mapping (no syscall overhead to change the mappings) and a simple way to handle unaligned accesses. - The critical point would be to keep standard soft MMU accesses for device access. An architectural change is needed to do that, but it seems easy to add. - This patch should work with qemu, not qemu-fast. The future of qemu-fast is to use a kernel module to have near native performances. It is not worthwhile to invest time in soft MMU or dynamic translation when you can just execute the code as is !


Piotras wrote:

The patch currently supports only x86 Linux host and requires that you are able to build working Qemu-fast. These limitations can be relaxed in the future. Also building qemu-fast may not be easy with some distributions. If you need assistance please post details of your environment -- hopefully somebody will be able to help.

You may need to download Qemu source and test Linux image:

Then create a build directory and run:
  > tar -zxf _PATH_TO_qemu-0.6.0.tar.gz
  > tar -zxf _PATH_TO_linux-test-0.5.1.tar.gz
  > cd qemu-0.6.0
  > ./configure --target-list=i386
  > make

Test qemu-fast:
  > ./i386/qemu-fast -L pc-bios -hda ../linux-test/linux.img

Then build patched version:
  > patch -p1 < _PATH_TO_fast-map-env-2.patch
  > make clean
  > make

Test patched Qemu-fast:
  > ./i386/qemu-fast -no-code-copy -L pc-bios -hda ../linux-test/linux.img

Notice that the patch is very experimental,


On Tue, 19 Oct 2004 17:39:38 -0700, Dan Sands <address@hidden> wrote:


Thanks for the patch.  Although I don't like showing my ignorance, how do I
use it?  I am new at this.


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