Latitude D620 [LWN.net]

Latitude D620

Posted Feb 21, 2007 1:08 UTC (Wed) by ncm (subscriber, #165)
Parent article: Dell users demand more Linux options (ZDNet UK)

I bought a Latitude D620 laptop late last year. It was only after I had used it for a couple of months that I discovered the Core Duo 7200 in it is actually a dual 64-bit processor, and would happily run a 64-bit kernel.

Now, of course the OS is already installed. It would be a fair bit of trouble to re-install with a 64-bit kernel and libraries. I have an idea that "multilibs" might make that simpler, but don't know what would be involved. Anyway the various binary audio and video codec files are compiled 32-bits, and wouldn't work with mplayer and xine. Or would they? If not, I wonder if you can run a 32-bit guest kernel under a 64-bit base kernel... There are so many questions, each probably answered fairly easily with some time and research. An LWN article answering them would be most valuable.

The benchmarks suggest that what we really want, for maximal performance on most uses, is a third build mode, both for kernel and (independently) for user-space programs: address operations would be limited to 32 bits, but programs (and OS) could use the extra registers and 64-bit instructions. It seems like a fairly small port of kernel and tool-chain. However, anybody putting it together would probably be cursed forever for complicating the x86 execution model even further.

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Latitude D620

Posted Feb 21, 2007 6:23 UTC (Wed) by khim (subscriber, #9252) [Link]

You can not run 32-bit binary codecs under 64-bit OS, but you can run 32-bit userspace under 64-bit kernel! And both chroot and exec work fine if you are trying to run 64-bit program so you can implement "64-bit jail" for your 64-bit programs. Of course usually it's done the other way around :-)

And even nasty nVidia drivers (latest versions) can be used in this mode - but it's sure pain to setup.

As for yet-another-execution model... Feel free to do this for userspace, but for kernel it's sheer lunacy: 32-bit kernel does so much work to support more then 2GB of RAM that any benefits from 32-bit pointers will be swallowed by this overhead. It's true for other architectures as well, BTW: PPC64, SPARC64 and so on often are installed with 64bit kernel and 32bit userspace. 64-bit pointers allow to remove a lot of cruft in kernel when you have more then 2GB of RAM - and 4GB of RAM already do not feel like outrageous amount, you can bet that 2 years from now it'll be norm...

Latitude D620

Posted Feb 21, 2007 7:35 UTC (Wed) by k8to (subscriber, #15413) [Link]

Well mostly true, but you can run a 32 bit app with 32 bit nasty win32codecs talking to a 64bit x server. It's a bit muddy what a "64bit os" means in this context. It's basically a matter of having all the 32 bit libraries the program in question needs.